03107nas a2200169 4500008004100000245011300041210006900154300001100223490000700234520253800241100001502779700001402794700001602808700002002824700002402844856006902868 2020 eng d00aSoil heterogeneity increases plant diversity after twenty years of manipulation during grassland restoration0 aSoil heterogeneity increases plant diversity after twenty years  ae020140 v303 a

The “environmental heterogeneity hypothesis” predicts that variability in resources promotes species coexistence, but few experiments support this hypothesis in plant communities. A previous 15‐yr test of this hypothesis in a prairie restoration experiment demonstrated a weak effect of manipulated soil resource heterogeneity on plant diversity. This response was attributed to a transient increase in richness following a post‐restoration supplemental propagule addition, occasionally higher diversity under nutrient enrichment, and reduced cover of a dominant species in a subset of soil treatments. Here, we report community dynamics under continuous propagule addition in the same experiment, corresponding to 16–20 yr of restoration, in response to altered availability and heterogeneity of soil resources. We also quantified traits of newly added species to determine if heterogeneity increases the amount and variety of niches available for new species to exploit. The heterogeneous treatment contained a factorial combination of altered nutrient availability and soil depth; control plots had no manipulations. Total diversity and richness were higher in the heterogeneous treatment during this 5‐yr study due to higher cover, diversity, and richness of previously established forbs, particularly in the N‐enriched subplots. All new species added to the experiment exhibited unique trait spaces, but there was no evidence that heterogeneous plots contained a greater variety of new species representing a wider range of trait spaces relative to the control treatment. The richness and cover of new species was higher in N‐enriched soil, but the magnitude of this response was small. Communities assembling under long‐term N addition were dominated by different species among subplots receiving added N, leading to greater dispersion of communities among the heterogeneous relative to control plots. Contrary to the deterministic mechanism by which heterogeneity was expected to increase diversity (greater variability in resources for new species to exploit), higher diversity in the heterogeneous plots resulted from destabilization of formerly grass‐dominated communities in N‐enriched subplots. While we do not advocate increasing available soil N at large scales, we conclude that the positive effect of environmental heterogeneity on diversity can take decades to materialize and depend on development of stochastic processes in communities with strong establishment limitation.

1 aBaer, S.G.1 aAdams, T.1 aScott, D.A.1 aBlair, John, M.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/10.1002/eap.201402579nas a2200169 4500008004100000245009300041210006900134300001400203490000700217520201300224100001802237700002502255700002202280700002102302700002402323856006202347 2019 eng d00aThe combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation0 acombined effects of an extreme heatwave and wildfire on tallgras a687 - 6970 v303 a

Questions: Climate extremes are predicted to become more common in many ecosystems. Climate extremes can promote and interact with disturbances, but the combined effects of climate extremes and disturbances have not been quantified in many ecosystems. In this study, we ask whether the dual impact of a climate extreme and concomitant disturbance (wildfire) has a greater affect than a climate extreme alone.
Location: Tallgrass prairie in the Konza Prairie Biological Station, northeastern Kansas, USA.
Methods: We quantified the response of a tallgrass prairie plant community to a 2‐year climate extreme of low growing‐season precipitation and high temperatures. In the first year of the climate extreme, a subset of plots was burned by a growing‐season wildfire. This natural experiment allowed us to compare community responses to a climate extreme with and without wildfire.
Results: In plots exposed to the climate extreme but not wildfire, community structure, diversity, and composition showed minor to insignificant changes, such as a 20% reduction in grass cover and a slight increase in species diversity. Plots exposed to both the climate extreme and wildfire underwent larger changes, including an 80% reduction in grass cover, 50% increase in forb cover, and increased plant diversity. Two years after the climate extreme, structural shifts in burned plots showed little sign of recovery, indicating a potentially lasting shift in plant community structure.
Conclusions: Our results suggest that community responses to climate extremes need to account for climate‐related disturbances — in this case, high temperatures, drought and wildfire. This response diverged from our expectation that heat, drought, and an additional fire would favor grasses. Although growing‐season wildfires in tallgrass prairie have been rare in recent decades, they will likely become more common with climate change, potentially leading to changes in grassland structure.

1 aRatajczak, Z.1 aChurchill, Amber, C.1 aLadwig, Laura, M.1 aTaylor, Jeff, H.1 aCollins, Scott., L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1275002916nas a2200229 4500008004100000245008900041210006900130300001100199490000700210520219900217100001702416700001602433700002402449700002602473700001802499700001702517700001802534700002602552700001602578700001702594856007502611 2019 eng d00aA comprehensive approach to analyzing community dynamics using rank abundance curves0 acomprehensive approach to analyzing community dynamics using ran ae028810 v103 a

Univariate and multivariate methods are commonly used to explore the spatial and temporaldynamics of ecological communities, but each has limitations, including oversimplification or abstractionof communities. Rank abundance curves (RACs) potentially integrate these existing methodologies bydetailing species-level community changes. Here, we had three goals:first, to simplify analysis of commu-nity dynamics by developing a coordinated set of R functions, and second, to demystify the relationshipsamong univariate, multivariate, and RACs measures, and examine how each is influenced by the commu-nity parameters as well as data collection methods. We developed new functions for studying temporalchanges and spatial differences in RACs in an update to the R package library(“codyn”), alongside othernew functions to calculate univariate and multivariate measures of community dynamics. We also devel-oped a new approach to studying changes in the shape of RAC curves. The R package update presentedhere increases the accessibility of univariate and multivariate measures of community change over timeand difference over space. Next, we use simulated and real data to assess the RAC and multivariate mea-sures that are output from our new functions, studying (1) if they are influenced by species richness andevenness, temporal turnover, and spatial variability and (2) how the measures are related to each other.Lastly, we explore the use of the measures with an example from a long-term nutrient addition experiment.Wefind that the RAC and multivariate measures are not sensitive to species richness and evenness andthat all the measures detail unique aspects of temporal change or spatial differences. We alsofind that spe-cies reordering is the strongest correlate of a multivariate measure of compositional change and explainsmost community change observed in long-term nutrient addition experiment. Overall, we show that spe-cies reordering is potentially an understudied determinant of community changes over time or differencesbetween treatments. The functions developed here should enhance the use of RACs to further explore thedynamics of ecological communities.

1 aAvolio, M.L.1 aCarroll, I.1 aCollins, Scott., L.1 aHouseman, Gregory, R.1 aHallett, L.M.1 aIsbell, F.L.1 aKoerner, S.E.1 aKomatsu, Kimberly, J.1 aSmith, M.D.1 aWilcox, K.R. uhttps://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecs2.288104634nas a2201021 4500008004100000245011700041210006900158300001600227490000800243520186900251100002602120700001702146700002402163700001902187700001702206700002602223700002302249700001802272700001702290700002202307700001902329700001402348700001502362700002402377700001402401700002202415700001702437700002002454700001802474700001702492700002102509700002802530700001702558700002402575700002202599700002602621700002102647700001802668700002402686700002402710700001102734700001902745700001902764700001502783700001402798700001402812700001802826700001202844700001602856700001902872700001902891700001602910700001902926700002002945700002002965700002202985700001103007700001403018700001903032700002403051700002303075700001703098700002503115700001903140700001803159700002003177700001603197700002403213700001803237700001503255700001903270700001603289700003203305700001603337700001703353700001703370700001603387700001803403700001703421700001903438700001403457700001503471700001703486700001103503700001903514700001803533856006103551 2019 eng d00aGlobal change effects on plant communities are magnified by time and the number of global change factors imposed0 aGlobal change effects on plant communities are magnified by time a17867-178730 v1163 a

Global change drivers (GCDs) are expected to alter community structure and consequently, the services that ecosystems provide. Yet, few experimental investigations have examined effects of GCDs on plant community structure across multiple ecosystem types, and those that do exist present conflicting patterns. In an unprecedented global synthesis of over 100 experiments that manipulated factors linked to GCDs, we show that herbaceous plant community responses depend on experimental manipulation length and number of factors manipulated. We found that plant communities are fairly resistant to experimentally manipulated GCDs in the short term (<10 y). In contrast, long-term (≥10 y) experiments show increasing community divergence of treatments from control conditions. Surprisingly, these community responses occurred with similar frequency across the GCD types manipulated in our database. However, community responses were more common when 3 or more GCDs were simultaneously manipulated, suggesting the emergence of additive or synergistic effects of multiple drivers, particularly over long time periods. In half of the cases, GCD manipulations caused a difference in community composition without a corresponding species richness difference, indicating that species reordering or replacement is an important mechanism of community responses to GCDs and should be given greater consideration when examining consequences of GCDs for the biodiversity–ecosystem function relationship. Human activities are currently driving unparalleled global changes worldwide. Our analyses provide the most comprehensive evidence to date that these human activities may have widespread impacts on plant community composition globally, which will increase in frequency over time and be greater in areas where communities face multiple GCDs simultaneously.

1 aKomatsu, Kimberly, J.1 aAvolio, M.L.1 aLemoine, Nathan, P.1 aIsbell, Forest1 aGrman, Emily1 aHouseman, Gregory, R.1 aKoerner, Sally, E.1 aJohnson, D.S.1 aWilcox, K.R.1 aAlatalo, Juha, M.1 aAnderson, J.P.1 aAerts, R.1 aBaer, S.G.1 aBaldwin, Andrew, H.1 aBates, J.1 aBeierkuhnlein, C.1 aBelote, R.T.1 aBlair, John, M.1 aBloor, J.M.G.1 aBohlen, P.J.1 aBork, Edward, W.1 aBoughton, Elizabeth, H.1 aBowman, W.D.1 aBritton, Andrea, J.1 aCahill, James, F.1 aChaneton, Enrique, J.1 aChiariello, N.R.1 aCheng, Jimin.1 aCollins, Scott., L.1 aCornelissen, J.H.C.1 aDu, G.1 aEskelinen, Anu1 aFirn, Jennifer1 aFoster, B.1 aGough, L.1 aGross, K.1 aHallett, L.M.1 aHan, X.1 aHarmens, H.1 aHovenden, M.J.1 aJagerbrand, A.1 aJentsch, A.1 aKern, Christel1 aKlanderud, Kari1 aKnapp, Alan, K.1 aKreyling, Juergen1 aLi, W.1 aLuo, Yiqi1 aMcCulley, R.L.1 aMcLaren, Jennie, R.1 aMegonigal, Patrick1 aMorgan, J.W.1 aOnipchenko, Vladimir1 aPennings, S.C.1 aPrevéy, J.S.1 aPrice, Jodi, N.1 aReich, P.B.1 aRobinson, Clare, H.1 aRussell, L.F.1 aSala, O.E.1 aSeabloom, E.W.1 aSmith, M.D.1 aSoudzilovskaia, Nadejda, A.1 aSouza, Lara1 aSuding, K.N.1 aSuttle, B.K.1 aSvejcar, T.1 aTilman, David1 aTognetti, P.1 aTurkington, R.1 aWhite, S.1 aXu, Zhuwen1 aYahdjian, L.1 aYu, Q.1 aZhang, Pengfei1 aZhang, Yunhai uhttps://www.pnas.org/content/early/2019/08/14/181902711603509nas a2200313 4500008004100000245008500041210006900126300001600195490000800211520253200219653000902751653001902760653003002779653001202809653002502821653002802846100003002874700002102904700002402925700002402949700002102973700002302994700002403017700001603041700002503057700002003082700001703102856007603119 2019 eng d00aShifts in plant functional composition following long-term drought in grasslands0 aShifts in plant functional composition following longterm drough a2133 - 21480 v1073 a

 1. Plant traits can provide unique insights into plant performance at the community scale. Functional composition, defined by both functional diversity and community-weighted trait means (CWMs), can affect the stability of above‐ground net primary production (ANPP) in response to climate extremes. Further complexity arises, however, when functional composition itself responds to environmental change. The duration of climate extremes, such as drought, is expected to increase with rising global temperatures; thus, understanding the impacts of long-term drought on functional composition and the corresponding effect that has on ecosystem function could improve predictions of ecosystem sensitivity to climate change.
 2. We experimentally reduced growing season precipitation by 66% across six temperate grasslands for 4 years and measured changes in three indices of functional diversity (functional dispersion, richness and evenness), community-weighted trait means and phylogenetic diversity (PD). Specific leaf area (SLA), leaf nitrogen content (LNC) and (at most sites) leaf turgor loss point (πTLP) were measured for species cumulatively representing ~90% plant cover at each site.
 3. Long-term drought led to increased community functional dispersion in three sites, with negligible effects on the remaining sites. Species re-ordering following the mortality/senescence of dominant species was the main driver of increased functional dispersion. The response of functional diversity was not consistently matched by changes in phylogenetic diversity. Community-level drought strategies (assessed as CWMs) largely shifted from drought tolerance to drought avoidance and/or escape strategies, as evidenced by higher community-weighted πTLP, SLA and LNC. Lastly, ecosystem drought sensitivity (i.e. relative reduction in ANPP in drought plots) was positively correlated with community-weighted SLA and negatively correlated with functional diversity.
 4. Synthesis. Increased functional diversity following long-term drought may stabilize ecosystem functioning in response to future drought. However, shifts in community-scale drought strategies may increase ecosystem drought sensitivity, depending on the nature and timing of drought. Thus, our results highlight the importance of considering both functional diversity and abundance‐weighted traits means of plant communities as their collective effect may either stabilize or enhance ecosystem sensitivity to drought.

10aANPP10aClimate change10acommunity weighted traits10aDrought10aFunctional diversity10aplant functional traits1 aGriffin-Nolan, Robert, J.1 aBlumenthal, D.M.1 aCollins, Scott., L.1 aFarkas, Timothy, E.1 aHoffman, Ava, M.1 aMueller, Kevin, E.1 aOcheltree, Troy, W.1 aSmith, M.D.1 aWhitney, Kenneth, D.1 aKnapp, Alan, K.1 aJones, Holly uhttps://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.1325202714nas a2200625 4500008004100000245006200041210006200103490000700165520105900172100001601231700001901247700002001266700001601286700001301302700001701315700001601332700001701348700001601365700002101381700002001402700002101422700002101443700002501464700002001489700002101509700001401530700001401544700002001558700002001578700001801598700002101616700002401637700001401661700002001675700001601695700001901711700001301730700001801743700001601761700001601777700002001793700002301813700002201836700001801858700001901876700001601895700001701911700001601928700002101944700002101965700001701986700001702003700001402020856005402034 2019 eng d00aSoil net nitrogen mineralisation across global grasslands0 aSoil net nitrogen mineralisation across global grasslands0 v103 a

Soil nitrogen mineralisation (Nmin), the conversion of organic into inorganic N, is important for productivity and nutrient cycling. The balance between mineralisation and immobilisation (net Nmin) varies with soil properties and climate. However, because most global-scale assessments of net Nmin are laboratory-based, its regulation under field-conditions and implications for real-world soil functioning remain uncertain. Here, we explore the drivers of realised (field) and potential (laboratory) soil net Nmin across 30 grasslands worldwide. We find that realised Nmin is largely explained by temperature of the wettest quarter, microbial biomass, clay content and bulk density. Potential Nmin only weakly correlates with realised Nmin, but contributes to explain realised net Nmin when combined with soil and climatic variables. We provide novel insights of global realised soil net Nmin and show that potential soil net Nmin data available in the literature could be parameterised with soil and climate data to better predict realised Nmin.

1 aRisch, A.C.1 aZimmermann, S.1 aOchoa-Hueso, R.1 aschütz, M.1 aFrey, B.1 aFirn, J., L.1 aFay, P., A.1 aHagedorn, F.1 aBorer, E.T.1 aSeabloom, E., W.1 aHarpole, W., S.1 aKnops, J., M. H.1 aMcCulley, R., L.1 aBroadbent, A., A. D.1 aStevens, C., J.1 aSilveira, M., L.1 aAdler, P.1 aBáez, S.1 aBiederman, L.A.1 aBlair, John, M.1 aBrown, C., S.1 aCaldeira, M., C.1 aCollins, Scott., L.1 aDaleo, P.1 adi Virgilio, A.1 aEbeling, A.1 aEisenhauer, N.1 aEsch, E.1 aEskelinen, A.1 aHagenah, N.1 aHautier, Y.1 aKirkman, K., P.1 aMacDougall, A., S.1 aMoore, Joslin, L.1 aPower, S., A.1 aProber, S., M.1 aRoscher, C.1 aSankaran, M.1 aSiebert, J.1 aSpeziale, K., L.1 aTognetti, P., M.1 aVirtanen, R.1 aYahdjian, L.1 aMoser, B. uhttp://www.nature.com/articles/s41467-019-12948-204794nas a2201093 4500008004100000245007500041210006900116300001400185490000600199520170000205100001801905700001601923700002001939700001601959700001701975700002401992700002002016700001802036700002002054700001202074700001902086700002502105700001902130700001702149700001602166700001502182700001702197700001702214700001502231700001602246700001702262700001702279700002802296700001802324700001702342700002202359700001702381700002202398700001802420700002402438700002002462700002502482700003002507700002902537700002602566700002002592700003002612700002302642700001602665700001902681700002202700700002802722700002002750700002402770700003002794700002002824700002602844700002702870700000502897700002502902700001702927700002002944700002302964700001502987700002203002700002303024700002203047700002203069700001703091700002203108700002203130700003003152700002303182700002103205700002303226700002203249700002103271700002703292700002203319700002403341700001703365700003203382700002003414700001603434700003203450700002203482700002503504700001703529700002003546700002303566700001503589700002903604856006703633 2018 eng d00aChange in dominance determines herbivore effects on plant biodiversity0 aChange in dominance determines herbivore effects on plant biodiv a1925-19320 v23 a

Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet, empirical support for the importance of site productivity as a mediator of these herbivore impacts is equivocal. Here, we synthesize data from 252 large-herbivore exclusion studies, spanning a 20-fold range in site productivity, to test an alternative hypothesis—that herbivore-induced changes in the competitive environment determine the response of plant biodiversity to herbivory irrespective of productivity. Under this hypothesis, when herbivores reduce the abundance (biomass, cover) of dominant species (for example, because the dominant plant is palatable), additional resources become available to support new species, thereby increasing biodiversity. By contrast, if herbivores promote high dominance by increasing the abundance of herbivory-resistant, unpalatable species, then resource availability for other species decreases reducing biodiversity. We show that herbivore-induced change in dominance, independent of site productivity or precipitation (a proxy for productivity), is the best predictor of herbivore effects on biodiversity in grassland and savannah sites. Given that most herbaceous ecosystems are dominated by one or a few species, altering the competitive environment via herbivores or by other means may be an effective strategy for conserving biodiversity in grasslands and savannahs globally.

1 aKoerner, S.E.1 aSmith, M.D.1 aBurkepile, D.E.1 aHanan, N.P.1 aAvolio, M.L.1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aLemoine, N.P.1 aForrestel, E.J.1 aEby, S.1 aThompson, D.I.1 aAguado-Santacruz, G.1 aAnderson, J.P.1 aAnderson, M.1 aAngassa, A.1 aBagchi, S.1 aBakker, E.S.1 aBastin, Gary1 aBaur, L.E.1 aBeard, K.H.1 aBeever, E.A.1 aBohlen, P.J.1 aBoughton, Elizabeth, H.1 aCanestro, Don1 aCesa, Ariela1 aChaneton, Enrique1 aCheng, Jimin1 aD’Antonio, C.M.1 aDeleglise, C.1 aDembélé, Fadiala.1 aDorrough, Josh.1 aEldridge, David., J.1 aFernandez-Going, Barbara.1 aFernández-Lugo, Silvia.1 aFraser, Lauchlan., H.1 aFreedman, Bill.1 aGarcía-Salgado, Gonzalo.1 aGoheen, Jacob., R.1 aGuo, Liang.1 aHusheer, Sean.1 aKarembé, Moussa.1 aKnops, Johannes., M. H.1 aKraaij, Tineke.1 aKulmatiski, Andrew.1 aKytöviita, Minna-Maarit.1 aLezama, Felipe.1 aLoucougaray, Gregory.1 aLoydi, Dan, G. Milchun1 a1 aMilton, Suzanne., J.1 aMorgan, J.W.1 aMoxham, Claire.1 aNehring, Kyle., C.1 aOlff, Han.1 aPalmer, Todd., M.1 aRebollo, Salvador.1 aRiginos, Corinna.1 aRisch, Anita., C.1 aRueda, Marta1 aSankaran, Mahesh.1 aSasaki, Takehiro.1 aSchoenecker, Kathryn., A.1 aSchultz, Nick., L.1 aSchütz, Martin.1 aSchwabe, Angelika.1 aSiebert, Frances.1 aSmit, Christian.1 aStahlheber, Karen., A.1 aStorm, Christian.1 aStrong, Dustin., J.1 aSu, Jishuai.1 aTiruvaimozhi, Yadugiri., V.1 aTyler, Claudia.1 aVal, James.1 aVandegehuchte, Martijn., L.1 aVeblen, Kari., E.1 aVermeire, Lance., T.1 aWard, David.1 aWu, Jianshuang.1 aYoung, Truman., P.1 aYu, Qiang.1 aZelikova, Tamara., Jane. uhttps://www.nature.com/articles/s41559-018-0696-y#article-info02813nas a2200217 4500008004100000245012300041210006900164300001600233490000700249520207200256100002302328700002402351700003002375700001902405700002502424700002702449700001602476700002002492700002102512856006202533 2018 eng d00aDrought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents0 aDrought consistently alters the composition of soil fungal and b a2818 - 28270 v243 a

The effects of short‐term drought on soil microbial communities remain largely unexplored, particularly at large scales and under field conditions. We used seven experimental sites from two continents (North America and Australia) to evaluate the impacts of imposed extreme drought on the abundance, community composition, richness, and function of soil bacterial and fungal communities. The sites encompassed different grassland ecosystems spanning a wide range of climatic and soil properties. Drought significantly altered the community composition of soil bacteria and, to a lesser extent, fungi in grasslands from two continents. The magnitude of the fungal community change was directly proportional to the precipitation gradient. This greater fungal sensitivity to drought at more mesic sites contrasts with the generally observed pattern of greater drought sensitivity of plant communities in more arid grasslands, suggesting that plant and microbial communities may respond differently along precipitation gradients. Actinobateria, and Chloroflexi, bacterial phyla typically dominant in dry environments, increased their relative abundance in response to drought, whereas Glomeromycetes, a fungal class regarded as widely symbiotic, decreased in relative abundance. The response of Chlamydiae and Tenericutes, two phyla of mostly pathogenic species, decreased and increased along the precipitation gradient, respectively. Soil enzyme activity consistently increased under drought, a response that was attributed to drought‐induced changes in microbial community structure rather than to changes in abundance and diversity. Our results provide evidence that drought has a widespread effect on the assembly of microbial communities, one of the major drivers of soil function in terrestrial ecosystems. Such responses may have important implications for the provision of key ecosystem services, including nutrient cycling, and may result in the weakening of plant–microbial interactions and a greater incidence of certain soil‐borne diseases.

1 aOchoa-Hueso, Raúl1 aCollins, Scott., L.1 aDelgado-Baquerizo, Manuel1 aHamonts, Kelly1 aPockman, William, T.1 aSinsabaugh, Robert, L.1 aSmith, M.D.1 aKnapp, Alan, K.1 aPower, Sally, A. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1411302388nas a2200205 4500008004100000022001400041245010800055210006900163300001400232490000800246520170300254100003001957700002801987700002202015700002602037700002402063700001602087700002002103856005902123 2018 eng d a1385-023700aLegacy effects of a regional drought on aboveground net primary production in six central US grasslands0 aLegacy effects of a regional drought on aboveground net primary  a505 - 5150 v2193 a

Global climate models predict increases in the frequency and severity of drought worldwide, directly affecting most ecosystem types. Consequently, drought legacy effects (drought-induced alterations in ecosystem function postdrought) are expected to become more common in ecosystems varying from deserts to grasslands to forests. Drought legacies in grasslands are usually negative and reduce ecosystem function, particularly after extended drought. Moreover, ecosystems that respond strongly to drought (high sensitivity) might be expected to exhibit the largest legacy effects the next year, but this relationship has not been established. We quantified legacy effects of a severe regional drought in 2012 on postdrought (2013) aboveground net primary productivity (ANPP) in six central US grasslands. We predicted that (1) the magnitude of drought legacy effects measured in 2013 would be positively related to the sensitivity of ANPP to the 2012 drought, and (2) drought legacy effects would be negative (reducing 2013 ANPP relative to that expected given normal precipitation amounts). The magnitude of legacy effects measured in 2013 was strongly related (r2 = 0.88) to the sensitivity of ANPP to the 2012 drought across these six grasslands. However, contrary to expectations, positive legacy effects (greater than expected ANPP) were more commonly observed than negative legacy effects. Thus, while the sensitivity of ANPP to drought may be a useful predictor of the magnitude of legacy effects, short-term (1-year) severe droughts may cause legacy effects that are more variable than those observed after multiyear droughts.

1 aGriffin-Nolan, Robert, J.1 aCarroll, Charles, J. W.1 aDenton, Elsie, M.1 aJohnston, Melissa, K.1 aCollins, Scott., L.1 aSmith, M.D.1 aKnapp, Alan, K. uhttp://link.springer.com/10.1007/s11258-018-0813-7.pdf02777nas a2200253 4500008004100000245012200041210006900163300001600232490000700248520194500255100002402200700002502224700001302249700002002262700002402282700002402306700002302330700002702353700002602380700002202406700002402428700002202452856004902474 2018 eng d00aRegional grassland productivity responses to precipitation during multiyear above- and below-average rainfall periods0 aRegional grassland productivity responses to precipitation durin a1935 - 19510 v243 a

There is considerable uncertainty in the magnitude and direction of changes in precipitation associated with climate change, and ecosystem responses are also uncertain. Multiyear periods of above- and below-average rainfall may foretell consequences of changes in rainfall regime. We compiled long-term aboveground net primary productivity (ANPP) and precipitation (PPT) data for eight North American grasslands, and quantified relationships between ANPP and PPT at each site, and in 1-3 year periods of above- and below-average rainfall for mesic, semiarid cool, and semiarid warm grassland types. Our objective was to improve understanding of ANPP dynamics associated with changing climatic conditions by contrasting PPT-ANPP relationships in above- and below-average PPT years to those that occurred during sequences of multiple above- and below-average years. We found differences in PPT-ANPP relationships in above- and below-average years compared to long-term site averages, and variation in ANPP not explained by PPT totals that likely are attributed to legacy effects. The correlation between ANPP and current- and prior-year conditions changed from year to year throughout multiyear periods, with some legacy effects declining, and new responses emerging. Thus, ANPP in a given year was influenced by sequences of conditions that varied across grassland types and climates. Most importantly, the influence of prior-year ANPP often increased with the length of multiyear periods, whereas the influence of the amount of current-year PPT declined. Although the mechanisms by which a directional change in the frequency of above- and below-average years imposes a persistent change in grassland ANPP require further investigation, our results emphasize the importance of legacy effects on productivity for sequences of above- vs. below-average years, and illustrate the utility of long-term data to examine these patterns.

1 aPetrie, Matthew, D.1 aPeters, Debra, P. C.1 aYao, Jin1 aBlair, John, M.1 aBurruss, Nathan, D.1 aCollins, Scott., L.1 aDerner, Justin, D.1 aGherardi, Laureano, A.1 aHendrickson, John, R.1 aSala, Osvaldo, E.1 aStarks, Patrick, J.1 aSteiner, Jean, L. uhttps://www.ncbi.nlm.nih.gov/pubmed/2926556802638nas a2200493 4500008004100000245011700041210006900158300001500227490000700242520117100249100002101420700001601441700002101457700001901478700002301497700001401520700001601534700002501550700001701575700002001592700001801612700002201630700002401652700002001676700001901696700002001715700001801735700002001753700002701773700002601800700002301826700002201849700001701871700002101888700002801909700002101937700002001958700001601978700002301994700001902017700002302036700002302059856006202082 2018 eng d00aSpatial heterogeneity in species composition constrains plant community responses to herbivory and fertilisation0 aSpatial heterogeneity in species composition constrains plant co a1364 -13710 v213 a

Environmental change can result in substantial shifts in community composition. The associated immigration and extinction events are likely constrained by the spatial distribution of species. Still, studies on environmental change typically quantify biotic responses at single spatial (time series within a single plot) or temporal (spatial beta diversity at single time points) scales, ignoring their potential interdependence. Here, we use data from a global network of grassland experiments to determine how turnover responses to two major forms of environmental change – fertilisation and herbivore loss – are affected by species pool size and spatial compositional heterogeneity. Fertilisation led to higher rates of local extinction, whereas turnover in herbivore exclusion plots was driven by species replacement. Overall, sites with more spatially heterogeneous composition showed significantly higher rates of annual turnover, independent of species pool size and treatment. Taking into account spatial biodiversity aspects will therefore improve our understanding of consequences of global and anthropogenic change on community dynamics.

1 aHodapp, Dorothee1 aBorer, E.T.1 aHarpole, Stanley1 aLind, Eric, M.1 aSeabloom, Eric, W.1 aAdler, P.1 aAlberti, J.1 aArnillas, Carlos, A.1 aBakker, J.D.1 aBiederman, L.A.1 aCadotte, Marc1 aCleland, Elsa, E.1 aCollins, Scott., L.1 aFay, Philip, A.1 aFirn, Jennifer1 aHagenah, Nicole1 aHautier, Yann1 aIribarne, Oscar1 aKnops, Johannes, M. H.1 aMcCulley, Rebecca, L.1 aMacDougall, Andrew1 aMoore, Joslin, L.1 aMorgan, J.W.1 aMortensen, Brent1 aLa Pierre, Kimberly, J.1 aRisch, Anita, C.1 aSchütz, Martin1 aPeri, Pablo1 aStevens, Carly, J.1 aWright, Justin1 aHillebrand, Helmut1 aGurevitch, Jessica uhttps://onlinelibrary.wiley.com/doi/pdf/10.1111/ele.1310203566nas a2200421 4500008004100000245014000041210006900181260001400250490000700264520229900271100001702570700001502587700002702602700002402629700002302653700002202676700001702698700002102715700001802736700002402754700001702778700002102795700001602816700001702832700002002849700001902869700001702888700002702905700002102932700002502953700001602978700001802994700002303012700002003035700001303055700001403068856006203082 2017 eng d00aAsymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments0 aAsymmetric responses of primary productivity to precipitation ex c4376-43850 v233 a

Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta-analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.

1 aWilcox, K.R.1 aShi, Zheng1 aGherardi, Laureano, A.1 aLemoine, Nathan, P.1 aKoerner, Sally, E.1 aHoover, David, L.1 aBork, Edward1 aByrne, Kerry, M.1 aCahill, James1 aCollins, Scott., L.1 aEvans, Sarah1 aGilgen, Anna, K.1 aHolub, Petr1 aJiang, Lifen1 aKnapp, Alan, K.1 aLeCain, Daniel1 aLiang, Junyi1 aGarcia-Palacios, Pablo1 aPeñuelas, Josep1 aPockman, William, T.1 aSmith, M.D.1 aSun, Shanghua1 aWhite, Shannon, R.1 aYahdjian, Laura1 aZhu, Kai1 aLuo, Yiqi uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1370603310nas a2200733 4500008004100000245008800041210006900129520119600198653002001394653002201414653001901436653001701455653002001472653001501492653002201507653002501529653002201554100001701576700002701593700002301620700001701643700002401660700001701684700002801701700002601729700001901755700002701774700002201801700002401823700002101847700002801868700001701896700002401913700002201937700002401959700001101983700001901994700001702013700001802030700001902048700002002067700002002087700002202107700001402129700002402143700002302167700002502190700001902215700002002234700002402254700002202278700001602300700003202316700001602348700001802364700002302382700001502405700002002420700001402440700001902454700001802473700002302491856006202514 2017 eng d00aAsynchrony among local communities stabilises ecosystem function of metacommunities0 aAsynchrony among local communities stabilises ecosystem function3 a

Temporal stability of ecosystem functioning increases the predictability and reliability of ecosystem services, and understanding the drivers of stability across spatial scales is important for land management and policy decisions. We used species-level abundance data from 62 plant communities across five continents to assess mechanisms of temporal stability across spatial scales. We assessed how asynchrony (i.e. different units responding dissimilarly through time) of species and local communities stabilised metacommunity ecosystem function. Asynchrony of species increased stability of local communities, and asynchrony among local communities enhanced metacommunity stability by a wide range of magnitudes (1–315%); this range was positively correlated with the size of the metacommunity. Additionally, asynchronous responses among local communities were linked with species’ populations fluctuating asynchronously across space, perhaps stemming from physical and/or competitive differences among local communities. Accordingly, we suggest spatial heterogeneity should be a major focus for maintaining the stability of ecosystem services at larger spatial scales.

10aAlpha diversity10aalpha variability10abeta diversity10aBiodiversity10aCoRRE data base10apatchiness10aPlant communities10aPrimary productivity10aspecies synchrony1 aWilcox, K.R.1 aTredennick, Andrew, T.1 aKoerner, Sally, E.1 aGrman, Emily1 aHallett, Lauren, M.1 aAvolio, M.L.1 aLa Pierre, Kimberly, J.1 aHouseman, Gregory, R.1 aIsbell, Forest1 aJohnson, David, Samuel1 aAlatalo, Juha, M.1 aBaldwin, Andrew, H.1 aBork, Edward, W.1 aBoughton, Elizabeth, H.1 aBowman, W.D.1 aBritton, Andrea, J.1 aCahill, James, F.1 aCollins, Scott., L.1 aDu, G.1 aEskelinen, Anu1 aGough, Laura1 aJentsch, Anke1 aKern, Christel1 aKlanderud, Kari1 aKnapp, Alan, K.1 aKreyling, Juergen1 aLuo, Yiqi1 aMcLaren, Jennie, R.1 aMegonigal, Patrick1 aOnipchenko, Vladimir1 aPrevéy, Janet1 aPrice, Jodi, N.1 aRobinson, Clare, H.1 aSala, Osvaldo, E.1 aSmith, M.D.1 aSoudzilovskaia, Nadejda, A.1 aSouza, Lara1 aTilman, David1 aWhite, Shannon, R.1 aXu, Zhuwen1 aYahdjian, Laura1 aYu, Qiang1 aZhang, Pengfei1 aZhang, Yunhai1 aGurevitch, Jessica uhttp://onlinelibrary.wiley.com/doi/10.1111/ele.12861/epdf03195nas a2200181 4500008004100000245008100041210006900122300001200191490000800203520260500211100001802816700002202834700002302856700002402879700001702903700001302920856008002933 2017 eng d00aChanges in spatial variance during a grassland to shrubland state transition0 aChanges in spatial variance during a grassland to shrubland stat a750-7600 v1053 a
  1. State transitions are changes in ecosystem structure and self-reinforcing feedbacks that are initiated when an exogenous driver variable crosses a threshold. Reversing state transitions is difficult and costly. While some state transitions are relatively rapid, many take years to decades. Outside of theoretical models, very little is known about slower state transitions and how they unfold in time and space.
  2. We quantified changes in spatial variance as a mesic grassland ecosystem shifts to a shrub-dominated state, using long-term experiments and simulations that maintain grasslands with annual fires or initiate a state transition to shrub dominance by decreasing fire frequency.
  3. In the experiments, the susceptibility to state transitions varied substantially in space. In the less frequent fire treatment, some plots became shrub-dominated around year 20 and grass extirpations began in year 25, but a third of the plots were still grass-dominated in year 37. Variable rates of state transition resulted in increasing spatial variance of grass cover over time, whereas shrub cover variance decreased. In the annually burned treatment, grasses remained dominant and the spatial variance of grass cover declined.
  4. In a separate experiment, less frequent fires were maintained for 23 years and then switched to annual fires. The switch to annual fires occurred shortly after grass variance started to increase and a majority of these plots quickly returned to a grass dominated state.
  5. In simulations, spatial variance remained low and average grass cover was high under frequent fires. If fire frequency decreased below a threshold, the ecosystem transitioned to shrubland, with a transient increase in the spatial variance of grass cover during the transition between states.
  6. Synthesis. Spatial variability in the rate and susceptibility to state transitions is indicative of a system with a patchy spatial structure, high spatial heterogeneity and low connectivity between patches. Increases in spatial variance can serve as an indication that some patches have begun a state transition and that management interventions are needed to avoid widespread transitions. This is one of the first empirical examples where altering management after an increase in spatial variance prevented state transitions.

 

1 aRatajczak, Z.1 aD’Odorico, P.D.1 aNippert, Jesse, B.1 aCollins, Scott., L.1 aBrunsell, N.1 aRavi, S. uhttps://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.1269603030nas a2200181 4500008004100000245010200041210006900143300001200212490000700224520241900231100001802650700002102668700002402689700002202713700001702735700002302752856007302775 2017 eng d00aThe interactive effects of press/pulse intensity and duration on regime shifts at multiple scales0 ainteractive effects of presspulse intensity and duration on regi a198-2180 v873 a

Regime shifts are difficult to reverse transitions that occur when an ecosystem reorganizes around a new set of self-reinforcing feedbacks. Regime shifts are predicted to occur when the intensity of some exogenous driver variable—such as temperature, annual harvest rate or nutrient addition rate—gradually approaches and crosses a threshold value, initiating a transition to an alternative state. However, many driver variables now change rapidly as presses or pulses, not gradually, requiring new conceptual frameworks for understanding and predicting regime shifts. We argue that identifying and controlling regime shifts in response to presses and pulses will require a greater focus on the duration, not just intensity, of changes in driver variables. In ecosystems with slower dynamics, transitions to an alternative state can take years to decades and as a result, a driver press with an intensity capable of resulting in a regime shift over long time-spans may fail to cause a regime shift when applied for shorter durations. We illustrate these ideas using simulations of local-scale alternative stable state models and preliminary evidence from long-term grazing and eutrophication experiments. The simulations also suggest that small changes in the duration of driver presses or pulses can determine whether an ecosystem recovers to its original state. These insights may extend to larger scales. In spatially extended simulations that included patchiness, spatial heterogeneity, and spatial connectivity, all patches recovered to their original state after shorter presses. However, once press duration exceeded a threshold, growing proportions of the landscape shifted to an alternative state as press duration increased. We observed similar patchy transitions in a catchment-scale experiment that reinstated frequent fires approximately halfway through a regime shift from grassland to shrubland, initiated by fire suppression. In both the local- and larger-scale models, the threshold duration needed to elicit regime shifts decreased as press intensity increased or when factors counteracting regime shifts weakened. These multiple lines of evidence suggest that conceptualizing regime shifts as an interactive function of the intensity and duration of driver changes will increase understanding of the varying effects of driver presses, pulses, and cycles on ecosystem dynamics.

1 aRatajczak, Z.1 aD'Odorico, Paolo1 aCollins, Scott., L.1 aBestelmeyer, B.T.1 aIsbell, F.L.1 aNippert, Jesse, B. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecm.124903239nas a2200313 4500008004100000245011900041210006900160300001400229490000700243520231400250100002002564700001702584700001402601700002002615700002402635700001602659700001702675700002402692700001702716700001602733700001502749700001902764700001502783700001502798700001702813700001702830700001602847856006202863 2017 eng d00aPushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years0 aPushing precipitation to the extremes in distributed experiments a1774-17820 v233 a

Intensification of the global hydrological cycle, ranging from larger individual precipitation events to more extreme multiyear droughts, has the potential to cause widespread alterations in ecosystem structure and function. With evidence that the incidence of extreme precipitation years (defined statistically from historical precipitation records) is increasing, there is a clear need to identify ecosystems that are most vulnerable to these changes and understand why some ecosystems are more sensitive to extremes than others. To date, opportunistic studies of naturally occurring extreme precipitation years, combined with results from a relatively small number of experiments, have provided limited mechanistic understanding of differences in ecosystem sensitivity, suggesting that new approaches are needed. Coordinated distributed experiments (CDEs) arrayed across multiple ecosystem types and focused on water can enhance our understanding of differential ecosystem sensitivity to precipitation extremes, but there are many design challenges to overcome (e.g., cost, comparability, standardization). Here, we evaluate contemporary experimental approaches for manipulating precipitation under field conditions to inform the design of ‘Drought-Net’, a relatively low-cost CDE that simulates extreme precipitation years. A common method for imposing both dry and wet years is to alter each ambient precipitation event. We endorse this approach for imposing extreme precipitation years because it simultaneously alters other precipitation characteristics (i.e., event size) consistent with natural precipitation patterns. However, we do not advocate applying identical treatment levels at all sites – a common approach to standardization in CDEs. This is because precipitation variability varies >fivefold globally resulting in a wide range of ecosystem-specific thresholds for defining extreme precipitation years. For CDEs focused on precipitation extremes, treatments should be based on each site's past climatic characteristics. This approach, though not often used by ecologists, allows ecological responses to be directly compared across disparate ecosystems and climates, facilitating process-level understanding of ecosystem sensitivity to precipitation extremes.

1 aKnapp, Alan, K.1 aAvolio, M.L.1 aBeier, C.1 aCarroll, C.J.W.1 aCollins, Scott., L.1 aDukes, J.S.1 aFraser, L.H.1 aGriffin-Nolan, R.J.1 aHoover, D.L.1 aJentsch, A.1 aLoik, M.E.1 aPhillips, R.P.1 aPost, A.K.1 aSala, O.E.1 aSlette, I.J.1 aYahdjian, L.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.1350401871nas a2200229 4500008004100000245010000041210006900141300000900210490000700219520113100226653002301357653002101380653002101401653002901422653002101451653002201472100002201494700002201516700002401538700001701562856006201579 2017 eng d00aSpecies reordering, not changes in richness, drives long-term dynamics in grassland communities0 aSpecies reordering not changes in richness drives longterm dynam a15650 v203 a

Determining how ecological communities will respond to global environmental change remains a challenging research problem. Recent meta-analyses concluded that most communities are undergoing compositional change despite no net change in local species richness. We explored how species richness and composition of co-occurring plant, grasshopper, breeding bird and small mammal communities in arid and mesic grasslands changed in response to increasing aridity and fire frequency. In the arid system, grassland and shrubland plant and breeding bird communities were undergoing directional change, whereas grasshopper and small mammal communities were stable. In the mesic system, all communities were undergoing directional change regardless of fire frequency. Despite directional change in composition in some communities, species richness of all communities did not change because compositional change resulted more from reordering of species abundances than turnover in species composition. Thus, species reordering, not changes in richness, explains long-term dynamics in these grass and shrub dominated communities.

10aCommunity dynamics10adesert grassland10adesert shrubland10afire; species reordering10aSpecies richness10atallgrass prairie1 aJones, Sydney, K.1 aRipplinger, Julie1 aCollins, Scott., L.1 aCoulson, Tim uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/ele.1286401743nas a2200145 4500008004100000245009500041210006900136520124400205100002201449700002401471700002001495700001601515700002001531856004601551 2016 eng d00aAltered rainfall patterns increase forb abundance and richness in native tallgrass prairie0 aAltered rainfall patterns increase forb abundance and richness i3 a

Models predict that precipitation variability will increase with climate change. We used a 15-year precipitation manipulation experiment to determine if altering the timing and amount of growing season rainfall will impact plant community structure in annually burned, native tallgrass prairie. The altered precipitation treatment maintained the same total growing season precipitation as the ambient precipitation treatment, but received a rainfall regime of fewer, larger rain events, and longer intervals between events each growing season. Although this change in precipitation regime significantly lowered mean soil water content, overall this plant community was remarkably resistant to altered precipitation with species composition relatively stable over time. However, we found significantly higher forb cover and richness and slightly lower grass cover on average with altered precipitation, but the forb responses were manifest only after a ten-year lag period. Thus, although community structure in this grassland is relatively resistant to this type of altered precipitation regime, forb abundance in native tallgrass prairie may increase in a future characterized by increased growing season precipitation variability.

1 aJones, Sydney, K.1 aCollins, Scott., L.1 aBlair, John, M.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://www.nature.com/articles/srep2012001811nas a2200217 4500008004100000245005400041210005300095300001600148490000600164520117700170100001801347700001601365700002201381700001601403700001801419700001901437700001801456700001401474700002401488856008101512 2016 eng d00acodyn: An R package of community dynamics metrics0 acodyn An R package of community dynamics metrics a1146–11510 v73 a
  1. New analytical tools applied to long-term data demonstrate that ecological communities are highly dynamic over time. We developed an r package, library(“codyn”), to help ecologists easily implement these metrics and gain broader insights into ecological community dynamics.
  2. library(“codyn”) provides temporal diversity indices and community stability metrics. All functions are designed to be easily implemented over multiple replicates.
  3. Temporal diversity indices include species turnover, mean rank shifts and rate of community change over time. Community stability metrics calculate overall stability and patterns of species covariance and synchrony over time, and include a null-modelling method to test significance.
  4. Finally, library(“codyn”) contains vignettes that describe methods and reproduce figures from published papers to help users contextualize and apply functions to their own data.
1 aHallett, L.M.1 aJones, S.K.1 aMacDonald, A.A.M.1 aJones, M.B.1 aFlynn, D.F.B.1 aRipplinger, J.1 aSlaughter, P.1 aGries, C.1 aCollins, Scott., L. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.1256903068nas a2200145 4500008004100000245011000041210006900151300001300220490000700233520254900240100001502789700002002804700002402824856007402848 2016 eng d00aEnvironmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie0 aEnvironmental heterogeneity has a weak effect on diversity durin a94 - 1060 v863 a

Understanding what constrains the persistence of species in communities is at the heart of community assembly theory and its application to conserving and enhancing biodiversity. The “environmental heterogeneity hypothesis” predicts greater species coexistence in habitats with greater resource variability. In the context of community assembly, environmental heterogeneity may influence the variety and strength of abiotic conditions and competitive interactions (environmental filters) to affect the relative abundance of species and biodiversity. We manipulated key resources that influence plant diversity in tallgrass prairie (i.e., soil depth and nitrogen availability) to increase environmental heterogeneity prior to sowing native prairie species into a former agricultural field. We compared variability in nutrient availability, aboveground annual net primary productivity (ANPP), and the composition of species between replicate plots containing soil heterogeneity manipulations and plots with no resource manipulations (n = 4 per treatment) during the first 15 yr of community assembly as a test of the “environmental heterogeneity hypothesis.” The manipulations increased environmental heterogeneity, measured as the coefficient of variation in NO3-N availability and ANPP. Plant diversity, however, was similar and decayed exponentially and indiscriminately over time between the heterogeneity treatments. Species richness declined linearly over time in both heterogeneity treatments, but richness was higher in the more heterogeneous soil 2 yr following a second propagule addition 8 yr after the initial sowing. As a result, there was a lower rate of species loss over time in the more heterogeneous soil (0.60 species yr−1) relative to the control soil (0.96 species yr−1). Communities in each treatment exhibited strong convergence over time resulting from a shift in dominant species across all treatments and a gradual increase in the clonal C4 grass, Andropogon gerardii. We attribute the weak effect of heterogeneity on diversity to increasing dominance of a clonal species, which decreased the scale of soil treatments relative to plant size, dispersal limitation, and absence of a key driver (grazing) known to increase plant diversity under a frequent fire regime. Thus, steering community assembly to attain high biodiversity may depend more on manipulating processes that reduce dominance and facilitate the arrival of new species than promoting environmental heterogeneity.

1 aBaer, S.G.1 aBlair, John, M.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/15-0888.103182nas a2200181 4500008004100000245012000041210006900161300001400230490000800244520254700252100001802799700001702817700002802834700001702862700001602879700002402895856008102919 2016 eng d00aNutrient additions cause divergence of tallgrass prairie plant communities resulting in loss of ecosystem stability0 aNutrient additions cause divergence of tallgrass prairie plant c a1478-14870 v1043 a

1.Nitrogen (N) and phosphorus (P) deposition due to pollution and land-use change are dramatically altering biogeochemical cycles. These altered nutrient inputs affect plant communities by generally increasing dominance and reducing diversity, as well as altering community variability (heterogeneity). Less well studied are effects of changes in community variability on ecosystem functions, such as productivity, or the stability of those functions. 2.Here we use a twelve-year nutrient addition experiment in tallgrass prairie to determine variability in community responses to N and P additions and link these responses to ecosystem productivity and stability. We added two levels of N and four levels of P in a fully factorial design to 25-m2 plots in native tallgrass prairie in northeastern Kansas, USA. Each year percent cover of each species was measured in June and August in a 1-m2 subplot of each plot, and annual net primary productivity was measured in two 0.1-m2 subplots in each plot at the end of each growing season. 3.The addition of N and P together increased plant community variability across space (i.e., the replicates were significantly more different from each other in the N + P treatments than they were in the control treatment). We also found that variability of the plant community within a single plot through time increased with the addition of N alone and N and P together. The highest level of both spatial and temporal variability occurred in plots with the highest level of nutrient addition (10 g m−2 of both N and P). 4.While we found no linkage between spatial variability of community composition and the spatial stability of productivity, the temporal stability of productivity decreased with increasing temporal plant community variability. Additionally, the ability to predict the productivity response to growing season precipitation, a key environmental variable, also decreased under higher temporal community variability. 5.Synthesis. Using a 12-yr nutrient addition experiment, we found that nutrient addition leads to both spatial and temporal community variability in mesic tallgrass prairie. The changes in community variability through time were directly related to ecosystem stability. While overall shifts in community structure in response to nutrient additions are important, the change in variability of local communities has significant implications for our ability to predict how patterns of biodiversity and ecosystem function will respond to a rapidly changing world.

1 aKoerner, S.E.1 aAvolio, M.L.1 aLa Pierre, Kimberly, J.1 aWilcox, K.R.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1261002277nas a2200205 4500008004100000245009600041210006900137300001200206490000800218520162900226100001701855700001701872700001501889700002401904700001901928700001601947700001701963700001701980856007401997 2016 eng d00aThe sensitivity of carbon exchanges in Great Plains grasslands to precipitation variability0 asensitivity of carbon exchanges in Great Plains grasslands to pr a280-2940 v1213 a

In the Great Plains, grassland carbon dynamics differ across broad gradients of precipitation and temperature, yet finer-scale variation in these variables may also affect grassland processes. Despite the importance of grasslands, there is little information on how fine-scale relationships compare between them regionally. We compared grassland C exchanges, energy partitioning and precipitation variability in eight sites in the eastern and western Great Plains using eddy covariance and meteorological data. During our study, both eastern and western grasslands varied between an average net carbon sink and a net source. Eastern grasslands had a moderate vapor pressure deficit (VPD = 0.95 kPa) and high growing season gross primary productivity (GPP = 1010 ± 218 g C m−2 m−2 y−1). Western grasslands had a growing season with higher VPD (1.43 kPa) and lower GPP (360 ± 127 g C m−2 m−2 y−1). Western grasslands were sensitive to precipitation at daily timescales, whereas eastern grasslands were sensitive at monthly and seasonal timescales. Our results support the expectation that C exchanges in these grasslands differ as a result of varying precipitation regimes. Because eastern grasslands are less influenced by short-term variability in rainfall than western grasslands, the effects of precipitation change are likely to be more predictable in eastern grasslands because the timescales of variability that must be resolved are relatively longer. We postulate increasing regional heterogeneity in grassland C exchanges in the Great Plains in coming decades.

1 aPetrie, M.D.1 aBrunsell, N.1 aVargas, R.1 aCollins, Scott., L.1 aFlanagan, L.B.1 aHanan, N.P.1 aLitvak, M.E.1 aSuyker, A.E. uhttps://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JG00320502102nas a2200361 4500008004100000245011900041210006900160300001400229490000700243520104200250653004101292653000901333653001401342653001201356653002001368100001601388700002001404700002401424700002001448700001801468700001801486700001901504700002001523700001601543700001201559700002001571700001701591700001701608700001601625700001701641700001701658856006501675 2016 eng d00aShared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands0 aShared drivers but divergent ecological responses Insights from  a666 - 6820 v663 a

Fire and grazing, key determinants of structure and function of savanna grasslands worldwide, have been extensively altered by humans. We used existing long-term manipulations of fire and grazing in North American and South African mesic savanna grasslands, as well as new experiments, to determine whether the impacts of fire and grazing by large herbivores differed between these systems. We found that despite a body of literature suggesting that these savanna grasslands respond uniquely to fire and grazing, their ecosystem responses (aboveground productivity) were generally similar. In contrast, plant-community responses to fire and herbivores diverged strongly between systems. The differences in plant-community responses, as well as convergence in ecosystem function, were underpinned by a common mechanism: the response of grass dominance to changing fire and grazing regimes. As a result, divergent responses of plant communities to altered fire and grazing regimes did not preclude convergence in ecosystem function.

10aAboveground net primary productivity10afire10agrassland10aGrazing10aplant community1 aSmith, M.D.1 aKnapp, Alan, K.1 aCollins, Scott., L.1 aBurkepile, D.E.1 aKirkman, K.P.1 aKoerner, S.E.1 aThompson, D.I.1 aBlair, John, M.1 aBurns, C.E.1 aEby, S.1 aForrestel, E.J.1 aFynn, R.W.S.1 aGovender, N.1 aHagenah, N.1 aHoover, D.L.1 aWilcox, K.R. uhttps://academic.oup.com/bioscience/article/66/8/666/246414102605nas a2200397 4500008004100000245009200041210006900133300001500202490000700217520148900224100001801713700001501731700001601746700001801762700001601780700001501796700001901811700001501830700001701845700001201862700002401874700001701898700001301915700001901928700002801947700002101975700002001996700001902016700001702035700001702052700001702069700001402086700001602100700001602116856007502132 2015 eng d00aAnthropogenic nitrogen deposition predicts local grassland primary production worldwide0 aAnthropogenic nitrogen deposition predicts local grassland prima a1459 -14650 v963 a

Humans dominate many important Earth system processes including the nitrogen (N) cycle. Atmospheric N deposition affects fundamental processes such as carbon cycling, climate regulation, and biodiversity, and could result in changes to fundamental Earth system processes such as primary production. Both modelling and experimentation have suggested a role for anthropogenically altered N deposition in increasing productivity, nevertheless, current understanding of the relative strength of N deposition with respect to other controls on production such as edaphic conditions and climate is limited. Here we use an international multiscale data set to show that atmospheric N deposition is positively correlated to aboveground net primary production (ANPP) observed at the 1-m2 level across a wide range of herbaceous ecosystems. N deposition was a better predictor than climatic drivers and local soil conditions, explaining 16% of observed variation in ANPP globally with an increase of 1 kg N·ha−1·yr−1 increasing ANPP by 3%. Soil pH explained 8% of observed variation in ANPP while climatic drivers showed no significant relationship. Our results illustrate that the incorporation of global N deposition patterns in Earth system models are likely to substantially improve estimates of primary production in herbaceous systems. In herbaceous systems across the world, humans appear to be partially driving local ANPP through impacts on the N cycle.

1 aStevens, C.J.1 aLind, E.M.1 aHautier, Y.1 aHarpole, W.S.1 aBorer, E.T.1 aHobbie, S.1 aSeabloom, E.Q.1 aLadwig, L.1 aBakker, J.D.1 aChu, C.1 aCollins, Scott., L.1 aDavies, K.F.1 aFirn, J.1 aHillebrand, H.1 aLa Pierre, Kimberly, J.1 aMacDougall, A.S.1 aMelbourne, B.A.1 aMcCulley, R.L.1 aMorgan, J.W.1 aOrrock, J.L.1 aProber, S.M.1 aRisch, A.1 aSchultz, M.1 aWragg, P.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/14-1902.102530nas a2200241 4500008004100000245008400041210006900125300001300194490000800207520176300215653001901978653002501997653003402022653001802056653002302074100002002097700002002117700001702137700002802154700002402182700001602206856006602222 2015 eng d00aDifferential sensitivity to regional-scale drought in six central US grasslands0 aDifferential sensitivity to regionalscale drought in six central a949 -9570 v1773 a

Terrestrial ecosystems often vary dramatically in their responses to drought, but the reasons for this are unclear. With climate change forecasts for more frequent and extensive drought in the future, a more complete understanding of the mechanisms that determine differential ecosystem sensitivity to drought is needed. In 2012, the Central US experienced the fourth largest drought in a century, with a regional-scale 40 % reduction in growing season precipitation affecting ecosystems ranging from desert grassland to mesic tallgrass prairie. This provided an opportunity to assess ecosystem sensitivity to a drought of common magnitude in six native grasslands. We tested the prediction that drought sensitivity is inversely related to mean annual precipitation (MAP) by quantifying reductions in aboveground net primary production (ANPP). Long-term ANPP data available for each site (mean length = 16 years) were used as a baseline for calculating reductions in ANPP, and drought sensitivity was estimated as the reduction in ANPP per millimeter reduction in precipitation. Arid grasslands were the most sensitive to drought, but drought responses and sensitivity varied by more than twofold among the six grasslands, despite all sites experiencing 40 % reductions in growing season precipitation. Although drought sensitivity generally decreased with increasing MAP as predicted, there was evidence that the identity and traits of the dominant species, as well as plant functional diversity, influenced sensitivity. A more comprehensive understanding of the mechanisms leading to differences in drought sensitivity will require multi-site manipulative experiments designed to assess both biotic and abiotic determinants of ecosystem sensitivity.

10aClimate change10aFunctional diversity10aLong-term ecological research10aPrecipitation10aPrimary production1 aKnapp, Alan, K.1 aCarroll, C.J.W.1 aDenton, E.M.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3233-602791nas a2200337 4500008004100000022001400041245013400055210006900189260001600258300001400274490000800288520170200296653002901998653004202027653004902069653002202118653003102140100001602171700002802187700002402215700002002239700001602259700001802275700001502293700001402308700001702322700001702339700001702356700001402373856006602387 2015 eng d a0029-854900aGlobal environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments0 aGlobal environmental change and the nature of aboveground net pr cJan-04-2015 a935 - 9470 v1773 a

Many global change drivers chronically alter resource availability in terrestrial ecosystems. Such resource alterations are known to affect aboveground net primary production (ANPP) in the short term; however, it is unknown if patterns of response change through time. We examined the magnitude, direction, and pattern of ANPP responses to a wide range of global change drivers by compiling 73 datasets from long-term (>5 years) experiments that varied by ecosystem type, length of manipulation, and the type of manipulation. Chronic resource alterations resulted in a significant change in ANPP irrespective of ecosystem type, the length of the experiment, and the resource manipulated. However, the pattern of ecosystem response over time varied with ecosystem type and manipulation length. Continuous directional responses were the most common pattern observed in herbaceous-dominated ecosystems. Continuous directional responses also were frequently observed in longer-term experiments (>11 years) and were, in some cases, accompanied by large shifts in community composition. In contrast, stepped responses were common in forests and other ecosystems (salt marshes and dry valleys) and with nutrient manipulations. Our results suggest that the response of ANPP to chronic resource manipulations can be quite variable; however, responses persist once they occur, as few transient responses were observed. Shifts in plant community composition over time could be important determinants of patterns of terrestrial ecosystem sensitivity, but comparative, long-term studies are required to understand how and why ecosystems differ in their sensitivity to chronic resource alterations.

10aAboveground productivity10aHierarchical response framework (HRF)10aLong-Term Ecological Research (LTER) Network10aNutrient addition10aPrecipitation manipulation1 aSmith, M.D.1 aLa Pierre, Kimberly, J.1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aGross, K.L.1 aBarrett, J.E.1 aFrey, S.D.1 aGough, L.1 aMiller, R.J.1 aMorris, J.T.1 aRustad, L.E.1 aYarie, J. uhttps://link.springer.com/article/10.1007%2Fs00442-015-3230-902684nas a2200577 4500008004100000245005700041210005700098300001000155490000600165520123800171100001401409700001701423700001801440700001801458700001701476700001601493700001501509700002101524700001901545700001601564700001401580700002101594700001801615700001201633700001801645700002401663700001701687700001101704700001301715700001301728700001701741700001601758700001601774700001801790700001401808700001801822700001401840700001501854700001101869700001901880700002001899700001901919700002201938700001701960700001401977700001601991700001802007700001602025700001502041856005002056 2015 eng d00aGrassland productivity limited by multiple nutrients0 aGrassland productivity limited by multiple nutrients a150800 v13 a

Terrestrial ecosystem productivity is widely accepted to be nutrient limited1. Although nitrogen (N) is deemed a key determinant of aboveground net primary production (ANPP)2,3, the prevalence of co-limitation by N and phosphorus (P) is increasingly recognized4,​5,​6,​7,​8. However, the extent to which terrestrial productivity is co-limited by nutrients other than N and P has remained unclear. Here, we report results from a standardized factorial nutrient addition experiment, in which we added N, P and potassium (K) combined with a selection of micronutrients (K+μ), alone or in concert, to 42 grassland sites spanning five continents, and monitored ANPP. Nutrient availability limited productivity at 31 of the 42 grassland sites. And pairwise combinations of N, P, and K+μ co-limited ANPP at 29 of the sites. Nitrogen limitation peaked in cool, high latitude sites. Our findings highlight the importance of less studied nutrients, such as K and micronutrients, for grassland productivity, and point to significant variations in the type and degree of nutrient limitation. We suggest that multiple-nutrient constraints must be considered when assessing the ecosystem-scale consequences of nutrient enrichment.

1 aFay, P.A.1 aProber, S.M.1 aHarpole, W.S.1 aKnops, J.M.H.1 aBakker, J.D.1 aBorer, E.T.1 aLind, E.M.1 aMacDougall, A.S.1 aSeabloom, E.W.1 aWragg, P.D.1 aAdler, P.1 aBlumenthal, D.M.1 aBuckley, Y.M.1 aChu, C.1 aCleland, E.E.1 aCollins, Scott., L.1 aDavies, K.F.1 aDu, G.1 aFeng, X.1 aFirn, J.1 aGruner, D.S.1 aHagenah, N.1 aHautier, Y.1 aHeckman, R.W.1 aJin, V.L.1 aKirkman, K.P.1 aKlein, J.1 aLadwig, L.1 aLi, Q.1 aMcCulley, R.L.1 aMelbourne, B.A.1 aMitchell, C.E.1 aMoore, Joslin, L.1 aMorgan, J.W.1 aRisch, A.1 aschütz, M.1 aStevens, C.J.1 aWedin, D.A.1 aYang, L.H. uhttps://www.nature.com/articles/nplants20158002081nas a2200241 4500008004100000245008200041210006900123300001500192490000700207520135700214100001801571700001401589700001801603700002401621700001801645700001701663700001901680700001601699700001601715700001701731700001701748856007401765 2014 eng d00aBiotic mechanisms of community stability shift along a precipitation gradient0 aBiotic mechanisms of community stability shift along a precipita a1693 -17000 v953 a

Understanding how biotic mechanisms confer stability in variable environments is a fundamental quest in ecology, and one that is becoming increasingly urgent with global change. Several mechanisms, notably a portfolio effect associated with species richness, compensatory dynamics generated by negative species covariance and selection for stable dominant species populations can increase the stability of the overall community. While the importance of these mechanisms is debated, few studies have contrasted their importance in an environmental context. We analyzed nine long-term data sets of grassland species composition to investigate how two key environmental factors, precipitation amount and variability, may directly influence community stability and how they may indirectly influence stability via biotic mechanisms. We found that the importance of stability mechanisms varied along the environmental gradient: strong negative species covariance occurred in sites characterized by high precipitation variability, whereas portfolio effects increased in sites with high mean annual precipitation. Instead of questioning whether compensatory dynamics are important in nature, our findings suggest that debate should widen to include several stability mechanisms and how these mechanisms vary in importance across environmental gradients.

1 aHallett, L.M.1 aHsu, J.S.1 aCleland, E.E.1 aCollins, Scott., L.1 aDickson, T.L.1 aFarrer, E.C.1 aGherardi, L.A.1 aGross, K.L.1 aHobbs, R.J.1 aTurnbull, L.1 aSuding, K.N. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-0895.102883nas a2200193 4500008004100000245016700041210006900208300001500277490000800292520217100300100001702471700001802488700002802506700001702534700001702551700001602568700002402584856008102608 2014 eng d00aChanges in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above-ground productivity in a tallgrass prairie0 aChanges in plant community composition not diversity during a de a1649 -16600 v1023 a

Nutrient additions typically increase terrestrial ecosystem productivity, reduce plant diversity and alter plant community composition; however, the effects of P additions and interactions between N and P are understudied. We added both N (10 g m−2) and three levels of P (2.5, 5 and 10 g m−2) to a native, ungrazed tallgrass prairie burned biennially in northeastern Kansas, USA, to determine the independent and interactive effects of N and P on plant community composition and above-ground net primary productivity (ANPP). After a decade of nutrient additions, we found few effects of P alone on plant community composition, N alone had stronger effects, and N and P additions combined resulted in much larger effects than either alone. The changes in the plant community were driven by decreased abundance of C4 grasses, perhaps in response to altered interactions with mycorrhizal fungi, concurrent with increased abundance of non-N-fixing perennial and annual forbs. Surprisingly, this large shift in plant community composition had little effect on plant community richness, evenness and diversity. The shift in plant composition with N and P combined had large but variable effects on ANPP over time. Initially, N and N and P combined increased above-ground productivity of C4 grasses, but after 4 years, productivity returned to ambient levels as grasses declined in abundance and the community shifted to dominance by non-N-fixing and annual forbs. Once these forbs increased in abundance and became dominant, ANPP was more variable, with pulses in forb production only in years when the site was burned. Synthesis. We found that a decade of N and P additions interacted to drive changes in plant community composition, which had large effects on ecosystem productivity but minimal effects on plant community diversity. The large shift in species composition increased variability in ANPP over time as a consequence of the effects of burning. Thus, increased inputs of N and P to terrestrial ecosystems have the potential to alter stability of ecosystem function over time, particularly within the context of natural disturbance regimes.

1 aAvolio, M.L.1 aKoerner, S.E.1 aLa Pierre, Kimberly, J.1 aWilcox, K.R.1 aWilson, G.T.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.1231202945nas a2200229 4500008004100000245010700041210006900148300001300217490000700230520226300237100001202500700001702512700001402529700001702543700001702560700002402577700001802601700001602619700002002635700001202655856004802667 2014 eng d00aDifferential effects of extreme drought on production and respiration: Synthesis and modeling analysis0 aDifferential effects of extreme drought on production and respir a621 -6330 v113 a

Extremes in climate may severely impact ecosystem structure and function, with both the magnitude and rate of response differing among ecosystem types and processes. We conducted a modeling analysis of the effects of extreme drought on two key ecosystem processes, production and respiration, and, to provide a broader context, we complemented this with a synthesis of published results that cover a wide variety of ecosystems. The synthesis indicated that across a broad range of biomes, gross primary production (GPP) was generally more sensitive to extreme drought (defined as proportional reduction relative to average rainfall periods) than was ecosystem respiration (ER). Furthermore, this differential sensitivity between production and respiration increased as drought severity increased; it occurred only in grassland ecosystems, and not in evergreen needle-leaf and broad-leaf forests or woody savannahs. The modeling analysis was designed to enable a better understanding of the mechanisms underlying this pattern, and focused on four grassland sites arrayed across the Great Plains, USA. Model results consistently showed that net primary productivity (NPP) was reduced more than heterotrophic respiration (Rh) by extreme drought (i.e., 67% reduction in annual ambient rainfall) at all four study sites. The sensitivity of NPP to drought was directly attributable to rainfall amount, whereas the sensitivity of Rh to drought was driven by soil drying, reduced carbon (C) input and a drought-induced reduction in soil C content – a much slower process. However, differences in reductions in NPP and Rh diminished as extreme drought continued, due to a gradual decline in the soil C pool leading to further reductions in Rh. We also varied the way in which drought was imposed in the modeling analysis; it was either imposed by simulating reductions in rainfall event size (ESR) or by reducing rainfall event number (REN). Modeled NPP and Rh decreased more by ESR than REN at the two relatively mesic sites but less so at the two xeric sites. Our findings suggest that responses of production and respiration differ in magnitude, occur on different timescales, and are affected by different mechanisms under extreme, prolonged drought.

1 aShi, Z.1 aThomey, M.L.1 aMowll, M.1 aLitvak, M.E.1 aBrunsell, N.1 aCollins, Scott., L.1 aPockman, W.T.1 aSmith, M.D.1 aKnapp, Alan, K.1 aLuo, Y. uhttps://www.biogeosciences.net/11/621/2014/02880nas a2200541 4500008004100000245008200041210006900123300001300192490000800205520144500213653001701658653002201675653002201697100001601719700001901735700001601754700001401770700001801784700001901802700001501821700002101836700001801857700001701875700001801892700001201910700002401922700001401946700001901960700001701979700001401996700001302010700001702023700001402040700001602054700001802070700002802088700001102116700001902127700002002146700002202166700002302188700001702211700001402228700001702242700001602259700001502275856004802290 2014 eng d00aEutrophication weakens stabilizing effects of diversity in natural grasslands0 aEutrophication weakens stabilizing effects of diversity in natur a521 -5250 v5083 a

Studies of experimental grassland communities1, 2, 3, 4, 5, 6, 7 have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others1, 2. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change8, 9, 10, 11. Here we analyse diversity–stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally8. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.

10aBiodiversity10aCommunity ecology10aGrassland ecology1 aHautier, Y.1 aSeabloom, E.W.1 aBorer, E.T.1 aAdler, P.1 aHarpole, W.S.1 aHillebrand, H.1 aLind, E.M.1 aMacDougall, A.S.1 aStevens, C.J.1 aBakker, J.D.1 aBuckley, Y.M.1 aChu, C.1 aCollins, Scott., L.1 aDaleo, P.1 aDamschen, E.I.1 aDavies, K.F.1 aFay, P.A.1 aFirn, J.1 aGruner, D.S.1 aJin, V.L.1 aKlein, J.A.1 aKnops, J.M.H.1 aLa Pierre, Kimberly, J.1 aLi, W.1 aMcCulley, R.L.1 aMelbourne, B.A.1 aMoore, Joslin, L.1 aO’Halloran, L.R.1 aProber, S.M.1 aRisch, A.1 aSankaran, M.1 aSchuetz, M.1 aHector, A. uhttps://www.nature.com/articles/nature1301402325nas a2200133 4500008004100000245011900041210006900160300001200229490000700241520182700248100001802075700002402093856007402117 2014 eng d00aInteractive effects of grazing, drought, and fire on grassland plant communities in North America and South Africa0 aInteractive effects of grazing drought and fire on grassland pla a98 -1090 v953 a

Grazing, fire, and climate shape mesic grassland communities. With global change altering all three factors, understanding how grasslands respond to changes in these combined drivers may aid in projecting future changes in grassland ecosystems. We manipulated rainfall and simulated grazing (clipping) in two long-term fire experiments in mesic grasslands in North America (NA) and South Africa (SA). Despite their common drivers, grasslands in NA and SA differ in evolutionary history. Therefore, we expected community structure and production in NA and SA to respond differently to fire, grazing, and drought. Specifically, we hypothesized that NA plant community composition and production would be more responsive than the SA plant communities to changes in the drivers and their interactions, and that despite this expected stability of SA grasslands, drought would be the dominant factor controlling production, but grazing would play the primary role in determining community composition at both sites. Contrary to our hypothesis, NA and SA grasslands generally responded similarly to grazing, drought, and fire. Grazing increased diversity, decreased grass cover and production, and decreased belowground biomass at both sites. Drought alone minimally impacted plant community structure, and we saw similar treatment interactions at the two sites. Drought was not the primary driver of grassland productivity, but instead drought effects were similar to or less than grazing and fire. Even though these grasslands differed in evolutionary history, they responded similarly to our fire, grazing, and climate manipulations. Overall, we found community and ecosystem convergence in NA and SA grasslands. Grazing and fire are as important as climate in controlling mesic grassland ecosystems on both continents.

1 aKoerner, S.E.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-0526.102488nas a2200337 4500008004100000245011500041210006900156300001300225490000800238520150100246653001601747653000901763653001201772653002901784653002201813100001201835700002001847700001701867700001601884700001701900700001601917700001801933700001901951700001901970700001701989700002402006700001802030700002002048700001602068856006602084 2014 eng d00aLoss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa0 aLoss of a large grazer impacts savanna grassland plant communiti a293 -3030 v1753 a

Large herbivore grazing is a widespread disturbance in mesic savanna grasslands which increases herbaceous plant community richness and diversity. However, humans are modifying the impacts of grazing on these ecosystems by removing grazers. A more general understanding of how grazer loss will impact these ecosystems is hampered by differences in the diversity of large herbivore assemblages among savanna grasslands, which can affect the way that grazing influences plant communities. To avoid this we used two unique enclosures each containing a single, functionally similar large herbivore species. Specifically, we studied a bison (Bos bison) enclosure at Konza Prairie Biological Station, USA and an African buffalo (Syncerus caffer) enclosure in Kruger National Park, South Africa. Within these enclosures we erected exclosures in annually burned and unburned sites to determine how grazer loss would impact herbaceous plant communities, while controlling for potential fire-grazing interactions. At both sites, removal of the only grazer decreased grass and forb richness, evenness and diversity, over time. However, in Kruger these changes only occurred with burning. At both sites, changes in plant communities were driven by increased dominance with herbivore exclusion. At Konza, this was caused by increased abundance of one grass species, Andropogon gerardii, while at Kruger, three grasses, Themeda triandra, Panicum coloratum, and Digitaria eriantha increased in abundance.

10adisturbance10afire10aGrazing10aPlant community richness10aSpecies diversity1 aEby, S.1 aBurkepile, D.E.1 aFynn, R.W.S.1 aBurns, C.E.1 aGovender, N.1 aHagenah, N.1 aKoerner, S.E.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aCollins, Scott., L.1 aKirkman, K.P.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://link.springer.com/article/10.1007%2Fs00442-014-2895-902306nas a2200277 4500008004100000245012500041210006900166300001300235490000700248520144900255100001801704700002001722700001701742700001601759700001201775700001701787700001601804700001901820700001901839700001701858700002401875700001801899700002001917700001601937856007501953 2014 eng d00aPlant community response to loss of large herbivores differs between North American and South African savanna grasslands0 aPlant community response to loss of large herbivores differs bet a808 -8160 v953 a

Herbivory and fire shape plant community structure in grass-dominated ecosystems, but these disturbance regimes are being altered around the world. To assess the consequences of such alterations, we excluded large herbivores for seven years from mesic savanna grasslands sites burned at different frequencies in North America (Konza Prairie Biological Station, Kansas, USA) and South Africa (Kruger National Park). We hypothesized that the removal of a single grass-feeding herbivore from Konza would decrease plant community richness and shift community composition due to increased dominance by grasses. Similarly, we expected grass dominance to increase at Kruger when removing large herbivores, but because large herbivores are more diverse, targeting both grasses and forbs, at this study site, the changes due to herbivore removal would be muted. After seven years of large-herbivore exclusion, richness strongly decreased and community composition changed at Konza, whereas little change was evident at Kruger. We found that this divergence in response was largely due to differences in the traits and numbers of dominant grasses between the study sites rather than the predicted differences in herbivore assemblages. Thus, the diversity of large herbivores lost may be less important in determining plant community dynamics than the functional traits of the grasses that dominate mesic, disturbance-maintained savanna grasslands.

1 aKoerner, S.E.1 aBurkepile, D.E.1 aFynn, R.W.S.1 aBurns, C.E.1 aEby, S.1 aGovender, N.1 aHagenah, N.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aCollins, Scott., L.1 aKirkman, K.P.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/13-1828.102943nas a2200277 4500008004100000245008900041210006900130300001100199490000700210520211800217653003402335653001902369653001302388653001602401653001402417653002902431653001002460653001802470653001702488100001802505700002402523700002002547700002002567700001602587856006202603 2014 eng d00aRainfall variability has minimal effects on grassland recovery from repeated grazing0 aRainfall variability has minimal effects on grassland recovery f a36 -440 v253 a

Question Mesic grasslands experience a complex disturbance regime including frequent fire, grazing by large ungulates and strong inter-annual climate variability. As a result of climate change, growing season precipitation regimes are predicted to become more variable, with larger event sizes and longer dry periods resulting in more temporally dynamic soil moisture regimes. Increased climate variability is likely to interact with other disturbances, such as grazing, in grassland ecosystems. We investigated the individual and combined effects of increased rainfall variability and grazing on plant community composition, structure and function in an annually burned, native tallgrass prairie. Our overarching question was: are grazing impacts modified under a more variable precipitation regime? Location Konza Prairie, Kansas, USA. Methods Plots were established within a long-term rainfall manipulation experiment in which larger, but less frequent, rain events were imposed during the growing season without altering the total rain amount. We then simulated intense grazing pressure during one growing season by repeatedly clipping all graminoids to 5 cm and monitored recovery over 3 yr. Results Neither grazing nor rainfall treatments affected species richness; however, grazing decreased total and grass above-ground net primary production (ANPP) and increased forb ANPP relative to ungrazed plots. Grass stem density recovered from intense grazing under ambient rainfall but did not fully recover, even after 2 yr in the altered rainfall treatment. Conclusions We found that increased rainfall variability had little effect on tallgrass prairie structure and function, while grazing had large effects. Grazing and increased rainfall variability interacted to suppress grass stem density and delayed recovery relative to controls. Although stem density was reduced, individual stem size increased, resulting in no net change in ANPP. This suggests that ANPP in grazed and ungrazed North American tallgrass prairie may be relatively resilient under more temporally variable precipitation regimes.

10aAnnual net primary production10aClimate change10aClipping10adisturbance10adiversity10aGrass–forb interaction10aKonza10aPrecipitation10aStem density1 aKoerner, S.E.1 aCollins, Scott., L.1 aBlair, John, M.1 aKnapp, Alan, K.1 aSmith, M.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1206503618nas a2200385 4500008004100000245009200041210006900133300001300202490000700215520250400222653002202726653001502748653001902763653003702782653002002819653001302839653002202852653001302874653002202887653002702909100001602936700002402952700001602976700002002992700002003012700001603032700001703048700001603065700001803081700001903099700001903118700001703137700001603154856006203170 2014 eng d00aResponses to fire differ between South African and North American grassland communities0 aResponses to fire differ between South African and North America a793 -8040 v253 a

Question Does fire frequency affect mesic grassland plant community structure and composition similarly in North America and South Africa? Location Konza Prairie Biological Station (KNZ), Kansas, USA, and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa. Methods Plant community structure and composition were compared among annually burned, unburned and intermediate treatments within two long-term fire frequency manipulation experiments in native grasslands in North America and South Africa using comparable methodology over a 5-yr period. Because fire may reduce soil nitrogen (N) availability and thus affect plant community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs indirect mechanisms driving responses to fire. Results The total number of species was higher at URF (183) than at KNZ (57). Overall divergence in plant community response to fire frequency occurred despite similar responses to nutrient additions. At KNZ, more frequent fire resulted in dominance by a few, tall, deep-rooted rhizomatous grasses (e.g. Andropogon gerardii). On unburned sites, shorter, more shade-tolerant species such as Poa pratensis increased in abundance, although A. gerardii remained dominant. Species richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of grass species, including Themeda triandra, Tristachya leucothrix and Hyparrhenia hirta. Decreasing fire frequency reduced species richness and resulted in dominance by a few, relatively tall caespitose grasses such as Aristida junciformis. There was a complete turnover of dominant species between annually burned and unburned treatments at URF, while at KNZ A. gerardii and Sorghastrum nutans occurred across the range of treatments. N addition reduced species richness in both sites. Conclusions Different responses to fire frequency between KNZ and URF are likely linked to the dominant species and their characteristic traits, including height and method of clonal reproduction, with the rhizomatous growth form of A. gerardii dominating the North American grassland. South Africa does not have an equivalent grass species; instead, a range of tufted, non-rhizomatous species dominate across the fire frequency treatments at URF. Reductions in soil N due to frequent fire did not appear to be a common mechanism driving responses in community composition in these two grasslands.

10aCommunity ecology10aDivergence10aFire frequency10aKonza Prairie Biological Station10aMesic grassland10anitrogen10aNutrient addition10aRichness10atallgrass prairie10aUkulinga Research Farm1 aKirkman, K.1 aCollins, Scott., L.1 aSmith, M.D.1 aKnapp, Alan, K.1 aBurkepile, D.E.1 aBurns, C.E.1 aFynn, R.W.S.1 aHagenah, N.1 aKoerner, S.E.1 aMatchett, K.J.1 aThompson, D.I.1 aWilcox, K.R.1 aWragg, P.D. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.1213002431nas a2200373 4500008004100000245012200041210006900163300001500232490000700247520133300254100001801587700002401605700001901629700001501648700001601663700001801679700001601697700001701713700001801730700001901748700001901767700001301786700001901799700001701818700002101835700001801856700001801874700002001892700001401912700002401926700001901950700001401969856007401983 2014 eng d00aYou are not always what we think you eat: selective assimilation across multiple whole-stream isotopic tracer studies0 aYou are not always what we think you eat selective assimilation  a2757 -27670 v953 a

Analyses of 21 15N stable isotope tracer experiments, designed to examine food web dynamics in streams around the world, indicated that the isotopic composition of food resources assimilated by primary consumers (mostly invertebrates) poorly reflected the presumed food sources. Modeling indicated that consumers assimilated only 33–50% of the N available in sampled food sources such as decomposing leaves, epilithon, and fine particulate detritus over feeding periods of weeks or more. Thus, common methods of sampling food sources consumed by animals in streams do not sufficiently reflect the pool of N they assimilate. Isotope tracer studies, combined with modeling and food separation techniques, can improve estimation of N pools in food sources that are assimilated by consumers. Food web studies that use putative food samples composed of actively cycling (more readily assimilable) and refractory (less assimilable) N fractions may draw erroneous conclusions about diets, N turnover, and trophic linkages of consumers. By extension, food web studies using stoichiometric or natural abundance approaches that rely on an accurate description of food-source composition could result in errors when an actively cycling pool that is only a fraction of the N pool in sampled food resources is not accounted for.

1 aDodds, W., K.1 aCollins, Scott., L.1 aHamilton, S.K.1 aTank, J.L.1 aJohnson, S.1 aWebster, J.R.1 aSimon, K.S.1 aWhiles, M.R.1 aRantala, H.M.1 aMcDowell, W.H.1 aPeterson, S.D.1 aRiis, T.1 aCrenshaw, C.L.1 aThomas, S.A.1 aKristensen, P.B.1 aCheever, B.M.1 aFlecker, A.S.1 aGriffiths, N.A.1 aCrowl, T.1 aRosi-Marshall, E.J.1 aEl-Sabaawi, R.1 aMarti, E. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-2276.101778nas a2200325 4500008004100000245012500041210006900166300001300235490000700248520081800255100001701073700001601090700001801106700001601124700002201140700001701162700001701179700001801196700002401214700001601238700002001254700001301274700001301287700001201300700001601312700001601328700001801344700001901362856007101381 2013 eng d00aCoordinated distributed experiments: an emerging tool for testing global hypotheses in ecology and environmental science0 aCoordinated distributed experiments an emerging tool for testing a147 -1550 v113 a

There is a growing realization among scientists and policy makers that an increased understanding of today's environmental issues requires international collaboration and data synthesis. Meta-analyses have served this role in ecology for more than a decade, but the different experimental methodologies researchers use can limit the strength of the meta-analytic approach. Considering the global nature of many environmental issues, a new collaborative approach, which we call coordinated distributed experiments (CDEs), is needed that will control for both spatial and temporal scale, and that encompasses large geographic ranges. Ecological CDEs, involving standardized, controlled protocols, have the potential to advance our understanding of general principles in ecology and environmental science.

1 aFraser, L.H.1 aHenry, H.A.1 aCarlyle, C.N.1 aWhite, S.R.1 aBeierkuhnlein, C.1 aCahill, J.F.1 aCasper, B.B.1 aCleland, E.E.1 aCollins, Scott., L.1 aDukes, J.S.1 aKnapp, Alan, K.1 aLind, E.1 aLong, R.1 aLuo, Y.1 aReich, P.B.1 aSmith, M.D.1 aSternberg, M.1 aTurkington, R. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/11027903196nas a2200241 4500008004100000245010800041210006900149300001500218490000700233520244600240100001802686700002402704700001802728700001702746700001602763700001902779700001802798700001602816700001402832700001702846700001702863856007402880 2013 eng d00aSensitivity of grassland plant community composition to spatial vs. temporal variation in precipitation0 aSensitivity of grassland plant community composition to spatial  a1687 -16960 v943 a

Climate gradients shape spatial variation in the richness and composition of plant communities. Given future predicted changes in climate means and variability, and likely regional variation in the magnitudes of these changes, it is important to determine how temporal variation in climate influences temporal variation in plant community structure. Here, we evaluated how species richness, turnover, and composition of grassland plant communities responded to interannual variation in precipitation by synthesizing long-term data from grasslands across the United States. We found that mean annual precipitation (MAP) was a positive predictor of species richness across sites, but a positive temporal relationship between annual precipitation and richness was only evident within two sites with low MAP. We also found higher average rates of species turnover in dry sites that in turn had a high proportion of annual species, although interannual rates of species turnover were surprisingly high across all locations. Annual species were less abundant than perennial species at nearly all sites, and our analysis showed that the probability of a species being lost or gained from one year to the next increased with decreasing species abundance. Bray-Curtis dissimilarity from one year to the next, a measure of species composition change that is influenced mainly by abundant species, was insensitive to precipitation at all sites. These results suggest that the richness and turnover patterns we observed were driven primarily by rare species, which comprise the majority of the local species pools at these grassland sites. These findings are consistent with the idea that short-lived and less abundant species are more sensitive to interannual climate variability than longer-lived and more abundant species. We conclude that, among grassland ecosystems, xeric grasslands are likely to exhibit the greatest responsiveness of community composition (richness and turnover) to predicted future increases in interannual precipitation variability. Over the long term, species composition may shift to reflect spatial patterns of mean precipitation; however, perennial-dominated systems will be buffered against rising interannual variation, while systems that have a large number of rare, annual species will show the greatest temporal variability in species composition in response to rising interannual variability in precipitation.

1 aCleland, E.E.1 aCollins, Scott., L.1 aDickson, T.L.1 aFarrer, E.C.1 aGross, K.L.1 aGherardi, L.A.1 aHallett, L.M.1 aHobbs, R.J.1 aHsu, J.S.1 aSuding, K.N.1 aTurnbull, L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/12-1006.102410nas a2200205 4500008004100000245012000041210006900161300001500230490000700245520171400252653002401966653002701990653001802017653001802035653002502053653001802078100001802096700002402114856006602138 2013 eng d00aSmall-scale patch structure in North American and South African grasslands responds differently to grazing and fire0 aSmallscale patch structure in North American and South African g a1293 -13060 v283 a

Fire and grazing significantly impact small-scale patch structure and dynamics in savanna grasslands. We assessed small-scale grass-forb associations in long-term fire and grazing experiments in North America (NA) and Southern Africa (SA). Transects of 128 0.25 m2 contiguous quadrats were sampled in areas with different combinations of grazing (ungrazed, single grazer, or multiple grazers) and fire frequency (unburned or annually burned). We predicted that (1) the patch structure of each of the dominant grasses in NA and SA would respond similarly to fire and grazing, and (2) that forb richness would be correlated to grass patch structure. Semi-variance analysis was used to determine patch structure of dominant grasses and forb cover. Community structure responded similarly in NA and SA to fire, grazing, and fire-grazing interactions. Species richness, diversity, and community heterogeneity were significantly higher in unburned-grazed sites. Grazing significantly increased forb cover and decreased cover of the dominant grasses, and the effects of fire on community structure depended on the grazing regime. Contrary to our prediction, we found that small-scale patch structure of the dominant grass species in NA and SA responded differently to grazing and fire. We found strong grass patch structure in unburned-ungrazed grasslands in both sites; however, grazing and fire reduced patch structure in NA but not SA, and in no instance did grass patch structure influence forb community structure. We conclude that fire and grazing have larger impacts on small-scale patch structure in NA than they do in SA even though overall community structure responded similarly on both continents.

10aDominance-diversity10aGrass-forb interaction10aheterogeneity10aKonza Prairie10aKruger National Park10aSemi-variance1 aKoerner, S.E.1 aCollins, Scott., L. uhttps://link.springer.com/article/10.1007%2Fs10980-013-9866-002646nas a2200205 4500008004100000245010000041210006900141300001300210490000700223520198600230653001602216653000902232653001402241653001202255653003002267653002202297100002402319700002002343856007702363 2012 eng d00aEffects of fire, grazing and topographic variation on vegetation structure in tallgrass prairie0 aEffects of fire grazing and topographic variation on vegetation  a563 -5750 v233 a

Questions How do fire and grazing by bison affect the composition and structure of tallgrass prairie plant communities and their temporal stability? Are these responses modulated by topographic location? Location Konza Prairie Biological Station, Kansas, USA. Methods Plant community composition was monitored in permanent plots in native grassland sites receiving different long-term prescribed burning and bison grazing regimes across a topographic gradient (lowlands, slopes, uplands) following 20 yr of variable burning treatments and 13 yr of grazing by bison. A combination of multivariate analyses was used to determine how community structure, life forms and individual species responded to the accumulated effects of long-term fire and grazing by native bison in upland, slope and lowland soils. Results Species diversity was maximized in sites that were infrequently burned and grazed by bison with the strongest response on infrequently burned slope sites, while diversity was lowest on frequently burned ungrazed sites and on frequently burned slope sites. In general, grass cover was highest in infrequently burned ungrazed sites and lowest on frequently burned grazed sites, while forb richness was highest in infrequently burned and grazed sites. Community response to fire and grazing differed across the topographic gradient. In general, frequent burning favoured C4 grasses, which reduced the abundance of C3 forbs, especially in lowland sites. Responses of dominant grasses and forbs to fire and grazing varied depending on topographic position. Community stability was positively correlated with species richness. Conclusions Overall, we found that fire and grazing are the main determinants of plant community composition and structure in this grassland system, but that topography mediates these effects. A combination of bison grazing and periodic fire is necessary to maximize diversity and community stability across this native grassland landscape.

10adisturbance10afire10agrassland10aGrazing10aPlant community structure10aSpecies diversity1 aCollins, Scott., L.1 aCalabrese, L.B. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1654-1103.2011.01369.x01961nas a2200265 4500008004100000245010500041210006900146300001500215490000800230520116100238653001801399653001601417653001401433653002201447653001701469100001401486700001601500700001801516700001601534700002401550700001901574700001901593700001701612856006601629 2012 eng d00aIncorporating clonal growth form clarifies the role of plant height in response to nitrogen addition0 aIncorporating clonal growth form clarifies the role of plant hei a1053 -10620 v1693 a

Nutrient addition to grasslands consistently causes species richness declines and productivity increases. Competition, particularly for light, is often assumed to produce this result. Using a long-term dataset from North American herbaceous plant communities, we tested whether height and clonal growth form together predict responses to fertilization because neither trait alone predicted species loss in a previous analysis. Species with a tall-runner growth form commonly increased in relative abundance in response to added nitrogen, while short species and those with a tall-clumped clonal growth form often decreased. The ability to increase in size via vegetative spread across space, while simultaneously occupying the canopy, conferred competitive advantage, although typically only the abundance of a single species within each height-clonal growth form significantly responded to fertilization in each experiment. Classifying species on the basis of two traits (height and clonal growth form) increases our ability to predict species responses to fertilization compared to either trait alone in predominantly herbaceous plant communities.

10aClonal growth10aCompetition10agrassland10aNitrogen addition10aproductivity1 aGough, L.1 aGross, K.L.1 aCleland, E.E.1 aClark, C.M.1 aCollins, Scott., L.1 aFargione, J.E.1 aPennings, S.C.1 aSuding, K.N. uhttps://link.springer.com/article/10.1007%2Fs00442-012-2264-501996nas a2200325 4500008004100000245006100041210005900102300001300161490000700174520104500181653003601226653002401262653002801286653003201314653002801346100002001374700002401394700001701418700001501435700001801450700001801468700001401486700001901500700001801519700001601537700001801553700001601571700001901587856006401606 2012 eng d00aLong-term ecological research in a human-dominated world0 aLongterm ecological research in a humandominated world a342 -3530 v623 a

The US Long Term Ecological Research (LTER) Network enters its fourth decade with a distinguished record of achievement in ecological science. The value of long-term observations and experiments has never been more important for testing ecological theory and for addressing today's most difficult environmental challenges. The network's potential for tackling emergent continent-scale questions such as cryosphere loss and landscape change is becoming increasingly apparent on the basis of a capacity to combine long-term observations and experimental results with new observatory-based measurements, to study socioecological systems, to advance the use of environmental cyberinfrastructure, to promote environmental science literacy, and to engage with decisionmakers in framing major directions for research. The long-term context of network science, from understanding the past to forecasting the future, provides a valuable perspective for helping to solve many of the crucial environmental problems facing society today.

10acoupled natural–human systems10acyberinfrastructure10aenvironmental education10aenvironmental observatories10asocioecological systems1 aRobertson, G.P.1 aCollins, Scott., L.1 aFoster, D.R.1 aBrokaw, N.1 aDucklow, H.W.1 aGragson, T.L.1 aGries, C.1 aHamilton, S.K.1 aMcGuire, A.D.1 aMoore, J.C.1 aStanley, E.H.1 aWaide, R.B.1 aWilliams, M.W. uhttps://academic.oup.com/bioscience/article/62/4/342/24360102406nas a2200445 4500008004100000245018600041210006900227520093600296653002601232653001901258653002701277653001601304653002401320653001201344653001401356653001401370653002501384653001801409653002101427653002801448653004101476653002301517653001801540653001401558653003201572653002801604100001901632700001601651700001501667700002401682700001901706700001901725700001601744700002001760700001601780700001601796700001601812700001201828856012001840 2012 eng d00aLong-term trends in ecological systems: a basis for understanding responses to global change. USDA Agriculture Research Service Publication, Technical Bulletin 1931. Washington, D.C0 aLongterm trends in ecological systems a basis for understanding 3 a

Peters, D.P.C., C.M. Laney, A.E. Lugo, et al. 2013. Long-Term Trends in Ecological Systems: A Basis for Understanding Responses to Global Change. U.S. Department of Agriculture, Technical Bulletin Number 1931. The EcoTrends Editorial Committee sorted through vast amounts of historical and ongoing data from 50 ecological sites in the continental United States including Alaska, several islands, and Antarctica to present in a logical format the variables commonly collected. This report presents a subset of data and variables from these sites and illustrates through detailed examples the value of comparing longterm data from different ecosystem types. This work provides cross-site comparisons of ecological responses to global change drivers, as well as longterm trends in global change drivers and responses at site and continental scales. Site descriptions and detailed data also are provided in the appendix section.

10aatmospheric chemistry10aClimate change10across-site comparisons10adisturbance10aecological response10aecology10aecosystem10aEcoTrends10aexperimental forests10aglobal change10ahuman demography10ahuman population growth10aLong Term Ecological Research (LTER)10along-term datasets10aPrecipitation10arangeland10arangeland research stations10asurface water chemistry1 aPeters, D.P.C.1 aLaney, C.M.1 aLugo, A.E.1 aCollins, Scott., L.1 aDriscoll, C.T.1 aGroffman, P.M.1 aGrove, J.M.1 aKnapp, Alan, K.1 aKratz, T.K.1 aOhman, M.D.1 aWaide, R.B.1 aYao, J. uhttp://knz.lternet.edu/content/long-term-trends-ecological-systems-basis-understanding-responses-global-change-usda02050nas a2200313 4500008004100000245008100041210006900122300001300191490000700204520112700211653001901338653001801357653002301375653001701398653002801415100002001443700001601463700001701479700002401496700001601520700001901536700001701555700002801572700001801600700001901618700001701637700001801654856006401672 2012 eng d00aPast, present, and future roles of long-term experiments in the LTER Network0 aPast present and future roles of longterm experiments in the LTE a377 -3890 v623 a

The US National Science Foundation–funded Long Term Ecological Research (LTER) Network supports a large (around 240) and diverse portfolio of long-term ecological experiments. Collectively, these long-term experiments have (a) provided unique insights into ecological patterns and processes, although such insight often became apparent only after many years of study; (b) influenced management and policy decisions; and (c) evolved into research platforms supporting studies and involving investigators who were not part of the original design. Furthermore, this suite of long-term experiments addresses, at the site level, all of the US National Research Council's Grand Challenges in Environmental Sciences. Despite these contributions, we argue that the scale and scope of global environmental change requires a more-coordinated multisite approach to long-term experiments. Ideally, such an approach would include a network of spatially extensive multifactor experiments, designed in collaboration with ecological modelers that would build on and extend the unique context provided by the LTER Network.

10aClimate change10aglobal change10along-term research10aLTER Network10amultifactor experiments1 aKnapp, Alan, K.1 aSmith, M.D.1 aHobbie, S.E.1 aCollins, Scott., L.1 aFahey, T.J.1 aHansen, G.J.A.1 aLandis, D.A.1 aLa Pierre, Kimberly, J.1 aMelillo, J.M.1 aSeastedt, T.R.1 aShaver, G.R.1 aWebster, J.R. uhttps://academic.oup.com/bioscience/article/62/4/377/24376200678nas a2200205 4500008004100000245009300041210006900134300001600203490000700219100002400226700001800250700001600268700001500284700001400299700002000313700001700333700001700350700001500367856009000382 2012 eng d00aStability of tallgrass prairie during a 19-year increase in growing season precipitation0 aStability of tallgrass prairie during a 19year increase in growi a1450 - 14590 v261 aCollins, Scott., L.1 aKoerner, S.E.1 aPlaut, J.A.1 aOkie, J.G.1 aBrese, D.1 aCalabrese, L.B.1 aCarvajal, A.1 aEvanse, R.J.1 aNonaka, E. uhttps://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2435.2012.01995.x03337nas a2200349 4500008004100000245011600041210006900157300001300226490000600239520233700245653003902582653000902621653001002630653001502640653001202655100002002667700001702687700002002704700001302724700002002737700002202757700002402779700001702803700001802820700001602838700001402854700001702868700001702885700001602902700001302918856005602931 2012 eng d00aA test of two mechanisms proposed to optimize grassland aboveground primary productivity in response to grazing0 atest of two mechanisms proposed to optimize grassland abovegroun a357 -3650 v53 a

Aims Mesic grasslands have a long evolutionary history of grazing by large herbivores and as a consequence, grassland species have numerous adaptations allowing them to respond favourably to grazing. Although empirical evidence has been equivocal, theory predicts that such adaptations combined with alterations in resources can lead to grazing-induced overcompensation in aboveground net primary production (ANPP; grazed ANPP > ungrazed ANPP) under certain conditions. We tested two specific predictions from theory. First, overcompensation is more likely to occur in annually burned grasslands because limiting nutrients that would be lost with frequent fires are recycled through grazers and stimulate ANPP. Second, overcompensation of biomass lost to grazers is more likely to occur in unburned sites where grazing has the greatest effect on increasing light availability through alterations in canopy structure. Methods We tested these nutrient versus light-based predictions in grazed grasslands that had been annually burned or protected from fire for >20 years. We assessed responses in ANPP to grazing by large ungulates using both permanent and moveable grazing exclosures (252 exclosures from which biomass was harvested from 3192 quadrats) in a 2-year study. Study sites were located at the Konza Prairie Biological Station (KPBS) in North America and at Kruger National Park (KNP) in South Africa. At KPBS, sites were grazed by North American bison whereas in KNP sites were grazed either by a diverse suite of herbivores (e.g. blue wildebeest, Burchell’s zebra, African buffalo) or by a single large ungulate (African buffalo). Important Findings We found no evidence for overcompensation in either burned or unburned sites, regardless of grazer type. Thus, there was no support for either mechanism leading to overcompensation. Instead, complete compensation of total biomass lost to grazers was the most common response characterizing grazing–ANPP relationships with, in some cases, undercompensation of grass ANPP being offset by increased ANPP of forbs likely due to competitive release. The capability of these very different grass-dominated systems to maintain ANPP while being grazed has important implications for energy flow, ecosystem function and the trophic dynamics of grasslands.

10aaboveground net primary production10afire10aforbs10aherbivores10asavanna1 aKnapp, Alan, K.1 aHoover, D.L.1 aBlair, John, M.1 aBuis, G.1 aBurkepile, D.E.1 aChamberlain, A.J.1 aCollins, Scott., L.1 aFynn, R.W.S.1 aKirkman, K.P.1 aSmith, M.D.1 aBlake, D.1 aGovender, N.1 aO’Neal, P.1 aSchreck, T.1 aZinn, A. uhttps://academic.oup.com/jpe/article/5/4/357/90869501717nas a2200145 4500008004100000245008900041210006900130300001300199490000700212520121200219100001801431700002301449700002401472856007501496 2012 eng d00aWoody encroachment decreases diversity across North American grasslands and savannas0 aWoody encroachment decreases diversity across North American gra a697 -7030 v933 a

Woody encroachment is a widespread and acute phenomenon affecting grasslands and savannas worldwide. We performed a meta-analysis of 29 studies from 13 different grassland/savanna communities in North America to determine the consequences of woody encroachment on plant species richness. In all 13 communities, species richness declined with woody plant encroachment (average decline = 45%). Species richness declined more in communities with higher precipitation (r2 = 0.81) and where encroachment was associated with a greater change in annual net primary productivity (ANPP; r2 = 0.69). Based on the strong positive correlation between precipitation and ANPP following encroachment (r2 = 0.87), we hypothesize that these relationships occur because water-limited woody plants experience a greater physiological and demographic release as precipitation increases. The observed relationship between species richness and ANPP provides support for the theoretical expectation that a trade-off occurs between richness and productivity in herbaceous communities. We conclude that woody plant encroachment leads to significant declines in species richness in North American grassland/savanna communities.

1 aRatajczak, Z.1 aNippert, Jesse, B.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/11-1199.101479nas a2200529 4500008004100000245009400041210006900135300001300204490000700217100001300224700002200237700002100259700001600280700001900296700002400315700001800339700001800357700001600375700001800391700001700409700001500426700001800441700001700459700002300476700001400499700002400513700002200537700001800559700002000577700002800597700002000625700001600645700001700661700001900678700001400697700001700711700001700728700001800745700001200763700001500775700001600790700001400806700001600820700001800836700001800854856007700872 2011 eng d00aAbundance of introduced species at home predicts abundance away in herbaceous communities0 aAbundance of introduced species at home predicts abundance away  a274 -2810 v141 aFirn, J.1 aMoore, Joslin, L.1 aMacDougall, A.S.1 aBorer, E.T.1 aSeabloom, E.W.1 aHilleRisLambers, J.1 aHarpole, W.S.1 aCleland, E.E.1 aBrown, C.S.1 aKnops, J.M.H.1 aProber, S.M.1 aPyke, D.A.1 aFarrell, K.A.1 aBakker, J.D.1 aO’Halloran, L.R.1 aAdler, P.1 aCollins, Scott., L.1 aD’Antonio, C.M.1 aCrawley, M.J.1 aWolkovich, E.M.1 aLa Pierre, Kimberly, J.1 aMelbourne, B.A.1 aHautier, Y.1 aMorgan, J.W.1 aLeakey, A.D.B.1 aKay, A.D.1 aMcCulley, R.1 aDavies, K.F.1 aStevens, C.J.1 aChu, C.1 aHoll, K.D.1 aKlein, J.A.1 aFay, P.A.1 aHagenah, N.1 aKirkman, K.P.1 aBuckley, Y.M. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2010.01584.x02083nas a2200337 4500008004100000245008000041210006900121300001300190490000600203520111900209100002401328700002001352700001801372700002001390700001901410700001801429700001601447700001601463700001701479700001501496700002001511700001801531700001901549700001901568700001701587700001601604700002001620700001601640700001801656856007101674 2011 eng d00aAn integrated conceptual framework for long-term social-ecological research0 aintegrated conceptual framework for longterm socialecological re a351 -3570 v93 a

The global reach of human activities affects all natural ecosystems, so that the environment is best viewed as a social–ecological system. Consequently, a more integrative approach to environmental science, one that bridges the biophysical and social domains, is sorely needed. Although models and frameworks for social–ecological systems exist, few are explicitly designed to guide a long-term interdisciplinary research program. Here, we present an iterative framework, “Press–Pulse Dynamics” (PPD), that integrates the biophysical and social sciences through an understanding of how human behaviors affect “press” and “pulse” dynamics and ecosystem processes. Such dynamics and processes, in turn, influence ecosystem services –thereby altering human behaviors and initiating feedbacks that impact the original dynamics and processes. We believe that research guided by the PPD framework will lead to a more thorough understanding of social–ecological systems and generate the knowledge needed to address pervasive environmental problems.

1 aCollins, Scott., L.1 aCarpenter, S.R.1 aSwinton, S.M.1 aOrenstein, D.E.1 aChilders, D.L.1 aGragson, T.L.1 aGrimm, N.B.1 aGrove, J.M.1 aHarlan, S.L.1 aKaye, J.P.1 aKnapp, Alan, K.1 aKofinas, G.P.1 aMagnuson, J.J.1 aMcDowell, W.H.1 aMelack, J.M.1 aOgden, L.A.1 aRobertson, G.R.1 aSmith, M.D.1 aWhitmer, A.C. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/10006800693nas a2200193 4500008004100000245015300041210006900194300001500263490000700278100001800285700001600303700002400319700001900343700001400362700001600376700001900392700001700411856007100428 2011 eng d00aPatterns of trait convergence and divergence among native and exotic species in herbaceous plant communities are not modified by nitrogen enrichment0 aPatterns of trait convergence and divergence among native and ex a1327 -13380 v991 aCleland, E.E.1 aClark, C.M.1 aCollins, Scott., L.1 aFargione, J.E.1 aGough, L.1 aGross, K.L.1 aPennings, S.C.1 aSuding, K.N. uhttps://www.jstor.org/stable/41333056?seq=1#page_scan_tab_contents02630nas a2200637 4500008004100000245006300041210006300104300001500167490000800182520095600190100001401146700001901160700001601179700001901195700001601214700001501230700001801245700002101263700001601284700001901300700001701319700002001336700001601356700001801372700002001390700001401410700001801424700002401442700002101466700001801487700001901505700001701524700002001541700001401561700001301575700001501588700001801603700001701621700001601638700002401654700002001678700001401698700001201712700001801724700001601742700001801758700002801776700002001804700001101824700002101835700001901856700002001875700001901895700002201914856005601936 2011 eng d00aProductivity is a poor predictor of plant species richness0 aProductivity is a poor predictor of plant species richness a1750 -17530 v3333 a

For more than 30 years, the relationship between net primary productivity and species richness has generated intense debate in ecology about the processes regulating local diversity. The original view, which is still widely accepted, holds that the relationship is hump-shaped, with richness first rising and then declining with increasing productivity. Although recent meta-analyses questioned the generality of hump-shaped patterns, these syntheses have been criticized for failing to account for methodological differences among studies. We addressed such concerns by conducting standardized sampling in 48 herbaceous-dominated plant communities on five continents. We found no clear relationship between productivity and fine-scale (meters−2) richness within sites, within regions, or across the globe. Ecologists should focus on fresh, mechanistic approaches to understanding the multivariate links between productivity and richness.

1 aAdler, P.1 aSeabloom, E.W.1 aBorer, E.T.1 aHillebrand, H.1 aHautier, Y.1 aHector, A.1 aHarpole, W.S.1 aO'Halloran, L.R.1 aGrace, J.B.1 aAnderson, T.M.1 aBakker, J.D.1 aBiederman, L.A.1 aBrown, C.S.1 aBuckley, Y.M.1 aCalabrese, L.B.1 aChu, C.J.1 aCleland, E.E.1 aCollins, Scott., L.1 aCottingham, K.L.1 aCrawley, M.J.1 aDamschen, E.I.1 aDavies, K.F.1 aDeCrappeo, N.M.1 aFay, P.A.1 aFirn, J.1 aFrater, P.1 aGasarch, E.I.1 aGruner, D.S.1 aHagenah, N.1 aHilleRisLambers, J.1 aHumphries, H.C.1 aJin, V.L.1 aKay, A.1 aKirkman, K.P.1 aKlein, J.A.1 aKnops, J.M.H.1 aLa Pierre, Kimberly, J.1 aLambrinos, J.G.1 aLi, W.1 aMacDougall, A.S.1 aMcCulley, R.L.1 aMelbourne, B.A.1 aMitchell, C.E.1 aMoore, Joslin, L. uhttp://science.sciencemag.org/content/333/6050/175002826nas a2200193 4500008004100000245009900041210006900140300001500209490000700224520219200231100002102423700001702444700001502461700002002476700002002496700001802516700002402534856007402558 2010 eng d00aFire and grazing in a mesic tallgrass prairie: impacts on plant species and functional traits0 aFire and grazing in a mesic tallgrass prairie impacts on plant s a1651 -16590 v913 a

Fire is a globally distributed disturbance that impacts terrestrial ecosystems and has been proposed to be a global “herbivore.” Fire, like herbivory, is a top-down driver that converts organic materials into inorganic products, alters community structure, and acts as an evolutionary agent. Though grazing and fire may have some comparable effects in grasslands, they do not have similar impacts on species composition and community structure. However, the concept of fire as a global herbivore implies that fire and herbivory may have similar effects on plant functional traits. Using 22 years of data from a mesic, native tallgrass prairie with a long evolutionary history of fire and grazing, we tested if trait composition between grazed and burned grassland communities would converge, and if the degree of convergence depended on fire frequency. Additionally, we tested if eliminating fire from frequently burned grasslands would result in a state similar to unburned grasslands, and if adding fire into a previously unburned grassland would cause composition to become more similar to that of frequently burned grasslands. We found that grazing and burning once every four years showed the most convergence in traits, suggesting that these communities operate under similar deterministic assembly rules and that fire and herbivory are similar disturbances to grasslands at the trait-group level of organization. Three years after reversal of the fire treatment we found that fire reversal had different effects depending on treatment. The formerly unburned community that was then burned annually became more similar to the annually burned community in trait composition suggesting that function may be rapidly restored if fire is reintroduced. Conversely, after fire was removed from the annually burned community trait composition developed along a unique trajectory indicating hysteresis, or a time lag for structure and function to return following a change in this disturbance regime. We conclude that functional traits and species-based metrics should be considered when determining and evaluating goals for fire management in mesic grassland ecosystems.

1 aSpasojevic, M.J.1 aAicher, R.J.1 aKoch, G.R.1 aMarquardt, E.S.1 aMirotchnick, N.1 aTroxler, T.G.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/09-0431.102607nas a2200325 4500008004100000245011200041210006900153300001300222490000700235520168300242653000901925653000901934653001501943653001201958653001301970653001301983100001501996700002002011700002002031700001602051700002202067700001602089700002402105700001702129700001702146700001602163700001602179700002002195856006602215 2009 eng d00aControls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison0 aControls of aboveground net primary production in mesic savanna  a982 -9950 v123 a

Patterns and controls of annual aboveground net primary productivity (ANPP) are fundamental metrics of ecosystem functioning. It is generally assumed, but rarely tested, that determinants of ANPP in one region within a biome will operate similarly throughout that biome, as long as physiognomy and climate are broadly consistent. We tested this assumption by quantifying ANPP responses to fire, grazing history, and nitrogen (N) addition in North American (NA) and South African (SA) savanna grasslands. We found that total ANPP responded in generally consistent ways to fire, grazing history, and N addition on both continents. Annual fire in both NA and SA consistently stimulated total ANPP (28–100%) relative to unburned treatments at sites with deep soils, and had no effect on ANPP in sites with shallow soils. Fire did not affect total ANPP in sites with a recent history of grazing, regardless of whether a single or a diverse suite of large herbivores was present. N addition interacted strongly and consistently with fire regime in both NA and SA. In annually burned sites that were not grazed, total ANPP was stimulated by N addition (29–39%), but there was no effect of N fertilization in the absence of fire. In contrast, responses in forb ANPP to fire and grazing were somewhat divergent across this biome. Annual fire in NA reduced forb ANPP, whereas grazing increased forb ANPP, but neither response was evident in SA. Thus, despite a consistent response in total ANPP, divergent responses in forb ANPP suggest that other aspects of community structure and ecosystem functioning differ in important ways between these mesic savanna grasslands.

10aANPP10afire10aGrasslands10aGrazing10anitrogen10aSavannas1 aBuis, G.M.1 aBlair, John, M.1 aBurkepile, D.E.1 aBurns, C.E.1 aChamberlain, A.J.1 aChapman, P.1 aCollins, Scott., L.1 aFynn, R.W.S.1 aGovender, N.1 aKirkman, K.1 aSmith, M.D.1 aKnapp, Alan, K. uhttps://link.springer.com/article/10.1007%2Fs10021-009-9273-102353nas a2200145 4500008004100000245011800041210006900159300001500228490000700243520182300250100001602073700002002089700002402109856007402133 2009 eng d00aA framework for assessing ecosystem dynamics in response to chronic resource alterations induced by global change0 aframework for assessing ecosystem dynamics in response to chroni a3279 -32890 v903 a

In contrast to pulses in resource availability following disturbance events, many of the most pressing global changes, such as elevated atmospheric carbon dioxide concentrations and nitrogen deposition, lead to chronic and often cumulative alterations in available resources. Therefore, predicting ecological responses to these chronic resource alterations will require the modification of existing disturbance-based frameworks. Here, we present a conceptual framework for assessing the nature and pace of ecological change under chronic resource alterations. The “hierarchical-response framework” (HRF) links well-documented, ecological mechanisms of change to provide a theoretical basis for testing hypotheses to explain the dynamics and differential sensitivity of ecosystems to chronic resource alterations. The HRF is based on a temporal hierarchy of mechanisms and responses beginning with individual (physiological/metabolic) responses, followed by species reordering within communities, and finally species loss and immigration. Each mechanism is hypothesized to differ in the magnitude and rate of its effects on ecosystem structure and function, with this variation depending on ecosystem attributes, such as longevity of dominant species, rates of biogeochemical cycling, levels of biodiversity, and trophic complexity. Overall, the HRF predicts nonlinear changes in ecosystem dynamics, with the expectation that interactions with natural disturbances and other global-change drivers will further alter the nature and pace of change. The HRF is explicitly comparative to better understand differential sensitivities of ecosystems, and it can be used to guide the design of coordinated, cross-site experiments to enable more robust forecasts of contemporary and future ecosystem dynamics.

1 aSmith, M.D.1 aKnapp, Alan, K.1 aCollins, Scott., L. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/08-1815.102483nas a2200157 4500008004100000245014000041210006900181300001300250490000800263520190200271100001502173700002002188700001602208700002402224856007702248 2008 eng d00aInfluence of grazing and fire frequency on small-scale plant community structure and resource variability in native tallgrass prairie0 aInfluence of grazing and fire frequency on smallscale plant comm a859 -8660 v1173 a

In grasslands worldwide, grazing by ungulates and periodic fires are important forces affecting resource availability and plant community structure. It is not clear, however, whether changes in community structure are the direct effects of the disturbance (i.e. fire and grazing) or are mediated indirectly through changes in resource abundance and availability. In North American tallgrass prairies, fire and grazing often have disparate effects on plant resources and plant diversity, yet, little is known about the individual and interactive effects of fire and grazing on resource variability and how that variability relates to heterogeneity in plant community structure, particularly at small scales. We conducted a field study to determine the interactive effects of different long-term fire regimes (annual vs four-year fire frequency) and grazing by native ungulates (Bos bison) on small-scale plant community structure and resource variability (N and light) in native tallgrass prairie. Grazing enhanced light and nitrogen availability, but did not affect small-scale resource variability. In addition, grazing reduced the dominance of C4 grasses which enhanced species richness, diversity and community heterogeneity. In contrast, annual fire increased community dominance and reduced species richness and diversity, particularly in the absence of grazing, but had no effect on community heterogeneity, resource availability and resource variability. Variability in the abundance of resources showed no relationship with community heterogeneity at the scale measured in this study, however we found a relationship between community dominance and heterogeneity. Therefore, we conclude that grazing generated small-scale community heterogeneity in this mesic grassland by directly affecting plant community dominance, rather than indirectly through changes in resource variability.

1 aVeen, G.F.1 aBlair, John, M.1 aSmith, M.D.1 aCollins, Scott., L. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.0030-1299.2008.16515.x02076nas a2200229 4500008004100000245004500041210004500086300001500131490000700146520144400153100002401597700001701621700001801638700001401656700001901670700001601689700001601705700001401721700001901735700001601754856007601770 2008 eng d00aRank clocks and plant community dynamics0 aRank clocks and plant community dynamics a3534 -35410 v893 aSummarizing complex temporal dynamics in communities is difficult to achieve in a way that yields an intuitive picture of change. Rank clocks and rank abundance statistics provide a graphical and analytical framework for displaying and quantifying community dynamics. We used rank clocks, in which the rank order abundance for each species is plotted over time in temporal clockwise direction, to display temporal changes in species abundances and richness. We used mean rank shift and proportional species persistence to quantify changes in community structure in long-term data sets from fertilized and control plots in a late successional old field, frequently and infrequently burned tallgrass prairie, and Chihuahuan desert grassland and shrubland communities. Rank clocks showed that relatively constant species richness masks considerable temporal dynamics in relative species abundances. In the old field, fertilized plots initially experienced high mean rank shifts that stabilized rapidly below that of unfertilized plots. Rank shifts were higher in infrequently burned vs. annually burned tallgrass prairie and in desert grassland compared to shrubland vegetation. Proportional persistence showed that arid grasslands were more dynamic than mesic grasslands. We conclude that rank clocks and rank abundance statistics provide important insights into community dynamics that are often hidden by traditional univariate approaches.1 aCollins, Scott., L.1 aSuding, K.N.1 aCleland, E.E.1 aBatty, M.1 aPennings, S.C.1 aGross, K.L.1 aGrace, J.S.1 aGough, L.1 aFargione, J.E.1 aClark, C.M. uhttp://knz.lternet.edu/content/rank-clocks-and-plant-community-dynamics01892nas a2200241 4500008004100000245013500041210006900176300001300245490000700258520110800265100002001373700001901393700002401412700001701436700002101453700001601474700001701490700001601507700001701523700001601540700001701556856007701573 2008 eng d00aShrub encroachment in North American grasslands: Shifts in growth form dominance rapidly alters control of ecosystem carbon inputs0 aShrub encroachment in North American grasslands Shifts in growth a615 -6230 v143 a

Shrub encroachment into grass-dominated biomes is occurring globally due to a variety of anthropogenic activities, but the consequences for carbon (C) inputs, storage and cycling remain unclear. We studied eight North American graminoid-dominated ecosystems invaded by shrubs, from arctic tundra to Atlantic coastal dunes, to quantify patterns and controls of C inputs via aboveground net primary production (ANPP). Across a fourfold range in mean annual precipitation (MAP), a key regulator of ecosystem C input at the continental scale, shrub invasion decreased ANPP in xeric sites, but dramatically increased ANPP (>1000 g m−2) at high MAP, where shrub patches maintained extraordinarily high leaf area. Concurrently, the relationship between MAP and ANPP shifted from being nonlinear in grasslands to linear in shrublands. Thus, relatively abrupt (<50 years) shifts in growth form dominance, without changes in resource quantity, can fundamentally alter continental-scale pattern of C inputs and their control by MAP in ways that exceed the direct effects of climate change alone.

1 aKnapp, Alan, K.1 aBriggs, J., M.1 aCollins, Scott., L.1 aArcher, S.R.1 aBret-Harte, M.S.1 aEwers, B.E.1 aPeters, D.P.1 aYoung, D.R.1 aShaver, G.R.1 aPendall, E.1 aCleary, M.B. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2007.01512.x02030nas a2200253 4500008004100000245011100041210006900152300001100221490000700232520125100239100001801490700001601508700002401524700001901548700001401567700001601581700001901597700001701616700002001633700001601653700001501669700001701684856007501701 2008 eng d00aSpecies responses to nitrogen fertilization in herbaceous plant communities, and associated species traits0 aSpecies responses to nitrogen fertilization in herbaceous plant  a1175 -0 v893 a

This synthetic data set contains plant species relative abundance measures from 35 nitrogen (N) fertilization experiments conducted at 10 sites across North America. The data set encompasses the fertilization responses of 575 taxa from 1159 experimental plots. The methodology varied among experiments, in particular with regard to the type and amount of N added, plot size, species composition measure (biomass harvest, pin count, or percent cover), additional experimental manipulations, and experimental duration. At each site, each species has been classified according to a number of easily identified categorical functional traits, including life history, life form, the number of cotyledons, height relative to the canopy, potential for clonal growth, and nativity to the United States. Additional data are available for many sites, indicated by references to publications and web sites. Analyses of these data have shown that N enrichment significantly alters community composition in ways that are predictable on the basis of plant functional traits as well as environmental context. This data set could be used to answer a variety of questions about how plant community composition and structure respond to environmental changes.

1 aCleland, E.E.1 aClark, C.M.1 aCollins, Scott., L.1 aFargione, J.E.1 aGough, L.1 aGross, K.L.1 aPennings, S.C.1 aBowman, W.D.1 aRobertson, G.P.1 aSimpson, J.1 aTilman, D.1 aSuding, K.N. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/07-1104.101888nas a2200205 4500008004100000245009600041210006900137300001300206490000700219520118600226100001601412700001801428700002401446700001901470700001401489700001901503700001701522700001601539856012701555 2007 eng d00aEnvironmental and plant community determinants ofspecies loss following nitrogen enrichment0 aEnvironmental and plant community determinants ofspecies loss fo a596 -6070 v103 aGlobal energy use and food production have increased nitrogen inputs to ecosystems worldwide, impacting plant community diversity, composition, and function. Previous studies show considerable variation across terrestrial herbaceous ecosystems in the magnitude of species loss following nitrogen (N) enrichment. What controls this variation remains unknown. We present results from 23 N-addition experiments across North America, representing a range of climatic, soil and plant community properties, to determine conditions that lead to greater diversity decline. Species loss in these communities ranged from 0 to 65% of control richness. Using hierarchical structural equation modelling, we found greater species loss in communities with a lower soil cation exchange capacity, colder regional temperature, and larger production increase following N addition, independent of initial species richness, plant productivity, and the relative abundance of most plant functional groups. Our results indicate sensitivity to N addition is co-determined by environmental conditions and production responsiveness, which overwhelm the effects of initial community structure and composition.1 aClark, C.M.1 aCleland, E.E.1 aCollins, Scott., L.1 aFargione, J.E.1 aGough, L.1 aPennings, S.C.1 aSuding, K.N.1 aGrace, J.B. uhttp://knz.lternet.edu/content/environmental-and-plant-community-determinants-ofspecies-loss-following-nitrogen-enrichment02677nas a2200181 4500008004100000245008700041210006900128300001300197490000800210520203100218653003402249653001602283100002202299700001702321700002102338700002402359856011202383 2007 eng d00aMicrobial responses to nitrogen addition in three contrasting grassland ecosystems0 aMicrobial responses to nitrogen addition in three contrasting gr a349 -3590 v1543 a

The effects of global N enrichment on soil processes in grassland ecosystems have received relatively little study. We assessed microbial community response to experimental increases in N availability by measuring extracellular enzyme activity (EEA) in soils from three grasslands with contrasting edaphic and climatic characteristics: a semiarid grassland at the Sevilleta National Wildlife Refuge, New Mexico, USA (SEV), and mesic grasslands at Konza Prairie, Kansas, USA (KNZ) and Ukulinga Research Farm, KwaZulu-Natal, South Africa (SAF). We hypothesized that, with N enrichment, soil microbial communities would increase C and P acquisition activity, decrease N acquisition activity, and reduce oxidative enzyme production (leading to recalcitrant soil organic matter [SOM] accumulation), and that the magnitude of response would decrease with soil age (due to higher stabilization of enzyme pools and P limitation of response). Cellulolytic activities followed the pattern predicted, increasing 35–52% in the youngest soil (SEV), 10–14% in the intermediate soil (KNZ) and remaining constant in the oldest soil (SAF). The magnitude of phosphatase response did not vary among sites. N acquisition activity response was driven by the enzyme closest to its pH optimum in each soil: i.e., leucine aminopeptidase in alkaline soil, β-N-acetylglucosaminidase in acidic soil. Oxidative enzyme activity varied widely across ecosystems, but did not decrease with N amendment at any site. Likewise, SOM and %C pools did not respond to N enrichment. Between-site variation in both soil properties and EEA exceeded any treatment response, and a large portion of EEA variability (leucine aminopeptidase and oxidative enzymes), 68% as shown by principal components analysis, was strongly related to soil pH (r = 0.91, P < 0.001). In these grassland ecosystems, soil microbial responses appear constrained by a molecular-scale (pH) edaphic factor, making potential breakdown rates of SOM resistant to N enrichment.

10aExtracellular enzyme activity10aSoil carbon1 aZeglin, Lydia, H.1 aStursova, M.1 aSinsabaugh, R.L.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/microbial-responses-nitrogen-addition-three-contrasting-grassland-ecosystems02242nas a2200253 4500008004100000245007600041210006900117300001300186490000800199520145100207653001901658653001901677653001701696653002301713653001801736100001801754700001701772700001701789700002401806700001601830700001801846700001701864856010701881 2007 eng d00aStream insect occupancy-frequency patterns and metapopulation structure0 aStream insect occupancyfrequency patterns and metapopulation str a313 -3210 v1513 aAn understanding of the distribution patterns of organisms and the underlying factors is a fundamental goal of ecology. One commonly applied approach to visualize these is the analysis of occupancy-frequency patterns. We used data sets describing stream insect distributions from different regions of North America to analyze occupancy-frequency patterns and assess the effects of spatial scale, sampling intensity, and taxonomic resolution on these patterns. Distributions were dominated by satellite taxa (those occurring in ≤10% of sites), whereas the occurrence of core taxa (occurring in ≥90% of sites) determined the overall modality of occupancy-frequency patterns. The proportions of satellite taxa increased with spatial scale and showed positive relationships with sampling intensity (r 2=0.74–0.96). Furthermore, analyses of data sets from New York (USA) showed that generic-level assessments underestimated the satellite class and occasionally shifted occupancy-frequency distributions from unimodal to bimodal. Our results indicate that, regardless of species- or generic-level taxonomy, stream insect communities are characterized by satellite species and that the proportion of satellite species increases with spatial scale and sampling intensity. Thus, niche-based models of occupancy-frequency patterns better characterize stream insect communities than metapopulation models such as the core-satellite species hypothesis.10aaquatic insect10aCore-satellite10aDistribution10aSampling intensity10aspatial scale1 aHeatherly, T.1 aWhiles, M.R.1 aGibson, D.J.1 aCollins, Scott., L.1 aHuryn, A.D.1 aJackson, J.K.1 aPalmer, M.A. uhttp://knz.lternet.edu/content/stream-insect-occupancy-frequency-patterns-and-metapopulation-structure02600nas a2200133 4500008004100000245009900041210006900140300001500209490000700224520207400231100002402305700001602329856012102345 2006 eng d00aScale-dependent interaction of fire andgrazing on community heterogeneity in tallgrass prairie0 aScaledependent interaction of fire andgrazing on community heter a2058 -20670 v873 aNatural disturbances affect spatial and temporal heterogeneity in plant communities, but effects vary depending on type of disturbance and scale of analysis. In this study, we examined the effects of fire frequency (1-, 4-, and 20-yr intervals) and grazing by bison on spatial and temporal heterogeneity in species composition in tallgrass prairie plant communities. Compositional heterogeneity was estimated at 10-, 50-, and 200-m2 scales. For each measurement scale, we used the average Euclidean Distance (ED) between samples within a year (2000) to measure spatial heterogeneity and between all time steps (1993–2000) for each sample to measure temporal heterogeneity. The main effects of fire and grazing were scale independent. Spatial and temporal heterogeneity were lowest on annually burned sites and highest on infrequently burned (20-yr) sites at all scales. Grazing reduced spatial heterogeneity and increased temporal heterogeneity at all scales. The rate of community change over time decreased as fire frequency increased at all scales, whereas grazing had no effect on rate of community change over time at any spatial scale. The interactive effects of fire and grazing on spatial and temporal heterogeneity differed with scale. At the 10-m2 scale, grazing increased spatial heterogeneity in annually burned grassland but decreased heterogeneity in less frequently burned areas. At the 50-m2 scale, grazing decreased spatial heterogeneity on 4-yr burns but had no effect at other fire frequencies. At the 10-m2 scale, grazing increased temporal heterogeneity only on 1- and 20-yr burn sites. Our results show that the individual effects of fire and grazing on spatial and temporal heterogeneity in mesic prairie are scale independent, but the interactive effects of these disturbances on community heterogeneity change with scale of measurement. These patterns reflect the homogenizing impact of fire at all spatial scales, and the different frequency, intensity, and scale of patch grazing by bison in frequently burned vs. infrequently burned areas.1 aCollins, Scott., L.1 aSmith, M.D. uhttp://knz.lternet.edu/content/scale-dependent-interaction-fire-andgrazing-community-heterogeneity-tallgrass-prairie02704nas a2200205 4500008004100000245010700041210006900148300001300217490000800230520200200238100001902240700001602259700001802275700002402293700001402317700001602331700002002347700001702367856011402384 2005 eng d00aDo individual plant speciesshow predictable responses to nitrogen addition across multipleexperiments?0 aDo individual plant speciesshow predictable responses to nitroge a547 -5550 v1103 aA number of experiments have addressed how increases in nitrogen availability increase the productivity and decrease the diversity of plant communities. We lack, however, a rigorous mechanistic understanding of how changes in abundance of particular species combine to produce changes in community productivity and diversity. Single experiments cannot provide insight into this issue because each species occurs only once per experiment, and each experiment is conducted in only one location; thus, it is impossible from single experiments to determine whether responses of particular species are consistent across environments or dependent on the particular environmental context in which the experiment was conducted. To address this issue, we assembled a dataset of 20 herbaceous species that were each represented in at least 6 different fertilization experiments and tested whether responses were general across experiments. Of the 20 species, one consistently increased in relative abundance and five consistently decreased across replicate experiments. A partially-overlapping group of 8 species displayed responses to nitrogen that varied predictably among experiments as a function of geographic location, neighboring species, or a handful of other community characteristics (ANPP, precipitation, species richness, relative abundance of focal species in control plots, and community composition). Thus, despite modest replication and a limited number of predictor variables, we were able to identify consistent patterns in response of 10 out of 20 species across multiple experiments. We conclude that the responses of individual species to nitrogen addition are often predictable, but that in most cases these responses are functions of the abiotic or biotic environment. Thus, a rigorous understanding of how plant species respond to nitrogen addition will have to consider not only the traits of individual plant species, but also aspects of the communities in which those plants live.1 aPennings, S.C.1 aClark, C.M.1 aCleland, E.E.1 aCollins, Scott., L.1 aGough, L.1 aGross, K.L.1 aMilchunas, D.G.1 aSuding, K.N. uhttp://knz.lternet.edu/content/do-individual-plant-speciesshow-predictable-responses-nitrogen-addition-across01970nas a2200205 4500008004100000245009900041210006900140300001500209490000800224520126300232100001701495700002401512700001401536700001601550700001801566700001601584700002001600700001701620856012701637 2005 eng d00aFunctional and abundance based mechanisms explain diversity loss due to nitrogen fertilization0 aFunctional and abundance based mechanisms explain diversity loss a4387 -43920 v1023 aHuman activities have increased N availability dramatically in terrestrial and aquatic ecosystems. Extensive research demonstrates that local plant species diversity generally declines in response to nutrient enrichment, yet the mechanisms for this decline remain unclear. Based on an analysis of >900 species responses from 34 N-fertilization experiments across nine terrestrial ecosystems in North America, we show that both trait-neutral and trait-based mechanisms operate simultaneously to influence diversity loss as production increases. Rare species were often lost because of soil fertilization, randomly with respect to traits. The risk of species loss due to fertilization ranged from >60% for the rarest species to 10% for the most abundant species. Perennials, species with N-fixing symbionts, and those of native origin also experienced increased risk of local extinction after fertilization, regardless of their initial abundance. Whereas abundance was consistently important across all systems, functional mechanisms were often system-dependent. As N availability continues to increase globally, management that focuses on locally susceptible functional groups and generally susceptible rare species will be essential to maintain biodiversity.1 aSuding, K.N.1 aCollins, Scott., L.1 aGough, L.1 aClark, C.M.1 aCleland, E.E.1 aGross, K.L.1 aMilchunas, D.G.1 aPennings, S. uhttp://knz.lternet.edu/content/functional-and-abundance-based-mechanisms-explain-diversity-loss-due-nitrogen-fertilization02664nas a2200241 4500008004100000245013500041210006900176300001300245490000700258520183200265653001402097653002102111653001602132653002302148653001602171653002202187100001502209700002402224700002002248700001602268700002002284856011802304 2005 eng d00aSoil heterogeneity effects on tallgrass prairie community heterogeneity: anapplication of ecological theory to restoration ecology0 aSoil heterogeneity effects on tallgrass prairie community hetero a413 -4240 v133 aSpatial heterogeneity of resources can influence plant community composition and diversity in natural communities. We manipulated soil depth (two levels) and nutrient availability (three levels) to create four heterogeneity treatments (no heterogeneity, depth heterogeneity, nutrient heterogeneity, and depth + nutrient heterogeneity) replicated in an agricultural field seeded to native prairie species. Our objective was to determine whether resource heterogeneity influences species diversity and the trajectory of community development during grassland restoration. The treatments significantly increased heterogeneity of available inorganic nitrogen (N), soil water content, and light penetration. Plant diversity was indirectly related to resource heterogeneity through positive relationships with variability in productivity and cover established by the belowground manipulations. Diversity was inversely correlated with the average cover of the dominant grass, Switchgrass (Panicum virgatum), which increased over time in all heterogeneity treatments and resulted in community convergence among the heterogeneity treatments over time. The success of this cultivar across the wide range of resource availability was attributed to net photosynthesis rates equivalent to or higher than those of the native prairie plants in the presence of lower foliar N content. Our results suggest that resource heterogeneity alone may not increase diversity in restorations where a dominant species can successfully establish across the range of resource availability. This is consistent with theory regarding the role of ecological filters on community assembly in that the establishment of one species best adapted for the physical and biological conditions can play an inordinately important role in determining community structure.10agrassland10aPanicum virgatum10arestoration10asoil heterogeneity10aswitchgrass10atallgrass prairie1 aBaer, S.G.1 aCollins, Scott., L.1 aBlair, John, M.1 aFiedler, A.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/soil-heterogeneity-effects-tallgrass-prairie-community-heterogeneity-anapplication01950nas a2200241 4500008004100000245009200041210006900133300001300202490000600215520117800221100002001399700001601419700002401435700001701459700001301476700001601489700001501505700002401520700001401544700001501558700001901573856011601592 2004 eng d00aGenerality in ecology: testing North American grassland rules in South African savannas0 aGenerality in ecology testing North American grassland rules in  a483 -4910 v93 aEcology has emerged as a global science, and there is a pressing need to identify ecological rules – general principles that will improve its predictive capability for scientists and its usefulness for managers and policy makers. Ideally, the generality and limits of these ecological rules should be assessed using extensive, coordinated experiments that ensure consistency in design and comparability of data. To improve the design of these large-scale efforts, existing data should be used to test prospective ecological rules and to identify their limits and contingencies. As an example of this approach, we describe prospective rules for grassland responses to fire and rainfall gradients, identified from long-term studies of North American grasslands and tested with existing data from long-term experiments in South African savanna grasslands. Analyses indicated consistent effects of fire on the abundance of the dominant (grasses) and subdominant (forbs) flora on both continents, but no common response of grass or forb abundance across a rainfall gradient. Such analyses can inform future research designs to refine and more explicitly test ecological rules.1 aKnapp, Alan, K.1 aSmith, M.D.1 aCollins, Scott., L.1 aZambatis, N.1 aPeel, M.1 aEmery, S.M.1 aWojdak, J.1 aHorner-Devine, M.C.1 aBiggs, H.1 aKruger, J.1 aAndelman, S.J. uhttp://knz.lternet.edu/content/generality-ecology-testing-north-american-grassland-rules-south-african-savannas00502nas a2200121 4500008004100000245009400041210006900135300001100204490000700215100001800222700002400240856011600264 2004 eng d00aNeeded: A unified infrastructure to support long-term scientific research on public lands0 aNeeded A unified infrastructure to support longterm scientific r a18 -210 v141 aPringle, C.M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/needed-unified-infrastructure-support-long-term-scientific-research-public-lands03493nas a2200205 4500008004100000245009200041210006900133300001300202490000800215520280200223653001403025653001403039653001303053653002203066100001503088700002003103700002403123700002003147856012003167 2004 eng d00aPlant community responses to resource availability and heterogeneity during restoration0 aPlant community responses to resource availability and heterogen a617 -6290 v1393 aAvailability and heterogeneity of resources have a strong influence on plant community structure in undisturbed systems, as well as those recovering from disturbance. Less is known about the role of resource availability and heterogeneity in restored communities, although restoration provides a valuable opportunity to test our understanding of factors that influence plant community assembly. We altered soil nitrogen (N) availability and soil depth during a prairie restoration to determine if the availability and/or heterogeneity of soil resources influenced plant community composition in restored grassland communities. Plant community responses to three levels of N availability (ambient, enriched by fertilization, and reduced by carbon amendment) and two levels of soil depth (deep and shallow) were evaluated. In addition, we evaluated plant community responses to four whole plot heterogeneity treatments created from the six possible combinations of soil N availability and soil depth. The soil depth treatment had little influence on community structure during the first 3 years of restoration. Total diversity and richness declined over time under annual N enrichment, whereas diversity was maintained and richness increased over time in soil with reduced N availability. Non-native species establishment was lowest in reduced-N soil in the initial year, but their presence was negligible in all of the soil N treatments by the second year of restoration. Panicum virgatum, a native perennial C4 grass, was the dominant species in all soil N treatments by year three, but the magnitude of its dominance was lowest in the reduced-N soil and highest in enriched-N soil. Consequently, the relative cover of P. virgatum was strongly correlated with community dominance and inversely related to diversity. The differential growth response of P. virgatum to soil N availability led to a higher degree of community similarity to native prairie in the reduced-N treatment than in the enriched-N treatment. There were no differences in plant community structure among the four whole plot-level heterogeneity treatments, which all exhibited the same degree of similarity to native prairie. Diversity and community heterogeneity in the whole-plot treatments appeared to be regulated by the dominant species’ effect on light availability, rather than soil N heterogeneity per se. Our results indicate that a strong differential response of a dominant species to resource availability in a restored community can regulate community structure, diversity, and similarity to the native (or target) community, but the importance of resource heterogeneity in restoring diversity may be dampened in systems where a dominant species can successfully establish across a range of resource availability.10adiversity10agrassland10anitrogen10atallgrass prairie1 aBaer, S.G.1 aBlair, John, M.1 aCollins, Scott., L.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/plant-community-responses-resource-availability-and-heterogeneity-during-restoration01819nas a2200241 4500008004100000245010000041210006900141300001100210490000700221520104700228653002001275653000901295653001801304653001401322653001001336100001701346700002401363700001501387700001901402700001501421700001801436856012301454 2003 eng d00aDisturbance dynamics and ecological response: the contribution of long-term ecological research0 aDisturbance dynamics and ecological response the contribution of a46 -560 v533 aLong-term ecological research is particularly valuable for understanding disturbance dynamics over long time periods and placing those dynamics in a regional context. We highlighted three case studies from Long Term Ecological Research (LTER) Network sites that have contributed to understanding the causes and consequences of disturbance in ecological systems. The LTER Network significantly enhances the ability to study disturbance by (a) encompassing ecosystems subject to a wide range of disturbances, (b) providing a long-term baseline against which to detect change and measure ecosystem responses to disturbance, (c) permitting observation of slow or infrequent events, (d) facilitating the use of multiple research approaches, (e) providing a focus for modeling disturbance dynamics, and (f) contributing to land and resource management. Long-term research is crucial to understanding past, present, and future disturbance dynamics, and the LTER Network is poised to make continuing contributions to the understanding of disturbance.10abiotic invasion10afire10aheterogeneity10ahurricane10ascale1 aTurner, M.G.1 aCollins, Scott., L.1 aLugo, A.L.1 aMagnuson, J.J.1 aRupp, T.S.1 aSwanson, F.J. uhttp://knz.lternet.edu/content/disturbance-dynamics-and-ecological-response-contribution-long-term-ecological-research02608nas a2200229 4500008004100000245008400041210006900125300001300194490000800207520185900215653001902074653001802093653002902111653001802140653001802158100001202176700001902188700002002207700002002227700002402247856010702271 2003 eng d00aProductivity responses to altered rainfall patterns in a C4-dominated grassland0 aProductivity responses to altered rainfall patterns in a C4domin a245 -2510 v1373 aRainfall variability is a key driver of ecosystem structure and function in grasslands worldwide. Changes in rainfall patterns predicted by global climate models for the central United States are expected to cause lower and increasingly variable soil water availability, which may impact net primary production and plant species composition in native Great Plains grasslands. We experimentally altered the timing and quantity of growing season rainfall inputs by lengthening inter-rainfall dry intervals by 50%, reducing rainfall quantities by 30%, or both, compared to the ambient rainfall regime in a native tallgrass prairie ecosystem in northeastern Kansas. Over three growing seasons, increased rainfall variability caused by altered rainfall timing with no change in total rainfall quantity led to lower and more variable soil water content (0–30 cm depth), a ~10% reduction in aboveground net primary productivity (ANPP), increased root to shoot ratios, and greater canopy photon flux density at 30 cm above the soil surface. Lower total ANPP primarily resulted from reduced growth, biomass and flowering of subdominant warm-season C4 grasses while productivity of the dominant C4 grass Andropogon gerardii was relatively unresponsive. In general, vegetation responses to increased soil water content variability were at least equal to those caused by imposing a 30% reduction in rainfall quantity without altering the timing of rainfall inputs. Reduced ANPP most likely resulted from direct effects of soil moisture deficits on root activity, plant water status, and photosynthesis. Altered rainfall regimes are likely to be an important element of climate change scenarios in this grassland, and the nature of interactions with other climate change elements remains a significant challenge for predicting ecosystem responses to climate change.10aClimate change10aKonza Prairie10aNet primary productivity10aPrecipitation10asoil moisture1 aFay, P.1 aCarlisle, J.D.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/productivity-responses-altered-rainfall-patterns-c4-dominated-grassland03030nas a2200169 4500008004100000245009400041210006900135300001300204490000700217520241300224653002202637100001502659700002002674700002002694700002402714856012202738 2003 eng d00aSoil resources regulate productivity and diversity in newly established tallgrass prairie0 aSoil resources regulate productivity and diversity in newly esta a724 -7350 v843 aIn native tallgrass prairie, soil depth and nitrogen (N) availability strongly influence aboveground net primary productivity (ANPP) and plant species composition. We manipulated these factors in a newly restored grassland to determine if these resources similarly constrain productivity and diversity during the initial three years of grassland establishment. Four types of experimental plots with six treatment combinations of deep and shallow soil at reduced-, ambient-, and enriched-N availability formed the basis of this study. The soil responses to the experimental treatments were examined over three years, and patterns in diversity and productivity were examined in year 3. The soil depth treatment did not significantly affect soil carbon (C) and N pools or ANPP and diversity. A pulse amendment of C added to the soil prior to planting increased soil microbial biomass and decreased potential net N mineralization rates to effectively reduce N availability throughout the study. Nitrogen availability declined over time in nonamended soils as a result of plant establishment, but adding fertilizer N alleviated the increasing immobilization potential of the soil. The level of ANPP was lowest and diversity highest in the reduced-N treatment, whereas the enriched-N treatment resulted in high productivity, but low diversity. As a result, diversity was inversely correlated with productivity in these newly established communities. The same mechanism invoked to explain decreased diversity under nutrient enrichment in old-field ecosystems and native grasslands (e.g., reduced light availability with increased production) was supported in the restored prairie by the positive relationship between ANPP and intercepted light, and a strong correlation between light availability and diversity. The effects of nutrient availability on plant community composition (diversity and richness) were due primarily to the responses of prairie species, as the productivity of early successional, nonprairie species was less than 1% of total ANPP after three years of establishment. These results show that the effects of resource availability on productivity and diversity are similar in young and mature grasslands, and that manipulation of a limiting nutrient during grassland establishment can influence floristic composition, with consequences for long-term patterns of diversity in restored ecosystems.10atallgrass prairie1 aBaer, S.G.1 aBlair, John, M.1 aKnapp, Alan, K.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/soil-resources-regulate-productivity-and-diversity-newly-established-tallgrass-prairie00700nas a2200205 4500008004100000245008600041210006900127300001300196490000800209100001400217700001900231700001700250700001500267700001900282700001600301700002000317700002000337700002400357856011300381 2002 eng d00aAltered rainfall patterns, gas exchange and growth in C3 and C4 grassland species0 aAltered rainfall patterns gas exchange and growth in C3 and C4 g a549 -5570 v1631 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/altered-rainfall-patterns-gas-exchange-and-growth-c3-and-c4-grassland-species02486nas a2200157 4500008004100000245009000041210006900131300001300200490000700213520191500220653002202135100002402157700001602181700001902197856011202216 2002 eng d00aEffect of local and regional processes on plant species richness in tallgrass prairie0 aEffect of local and regional processes on plant species richness a571 -5790 v993 aHistorically, diversity in a community was often believed to result primarily from local processes, but recent evidence suggests that regional diversity may strongly influence local diversity as well. We used experimental and observational vegetation data from Konza Prairie, Kansas, USA, to determine if: (1) there is a relationship between local and regional richness in tallgrass prairie vegetation; (2) local dominance reduces local species richness; and (3) reducing local dominance increases local and regional species richness. We found a positive relationship between regional and local richness; however, this relationship varied with grazing, topography and fire frequency. The decline in variance explained in the grazed vegetation, in particular, suggested that local processes associated with grazing pressure on the dominant grasses strongly influenced local species richness. Experimental removal of one of the dominant grasses, Andropogon scoparius, from replicate plots resulted in a significant increase in local species richness compared to adjacent reference plots. Overall all sites, species richness was higher in grazed (192 spp.) compared to ungrazed (158 spp.) areas. Across the Konza Prairie landscape, however, there were no significant differences in the frequency distribution of species occurrences, or in the relationship between the number of sites occupied and average abundance in grazed compared to ungrazed areas. Thus, local processes strongly influenced local richness in this tallgrass prairie, but local processes did not produce different landscape-scale patterns in species distribution and abundance. Because richness was enhanced at all spatial scales by reducing the abundance of dominant species, we suggest that species richness in tallgrass prairie results from feedbacks between, and interactions among, processes operating at multiple scales in space and time.10atallgrass prairie1 aCollins, Scott., L.1 aGlenn, S.M.1 aBriggs, J., M. uhttp://knz.lternet.edu/content/effect-local-and-regional-processes-plant-species-richness-tallgrass-prairie01540nas a2200229 4500008004100000245009000041210006900131300001500200490000800215520084900223100002001072700001401092700002001106700002401126700001601150700001901166700001701185700001701202700001501219700001901234856005701253 2002 eng d00aRainfall variability, carbon cycling and plant species diversity in a mesic grassland0 aRainfall variability carbon cycling and plant species diversity  a2202 -22050 v2983 a

Ecosystem responses to increased variability in rainfall, a prediction of general circulation models, were assessed in native grassland by reducing storm frequency and increasing rainfall quantity per storm during a 4-year experiment. More extreme rainfall patterns, without concurrent changes in total rainfall quantity, increased temporal variability in soil moisture and plant species diversity. However, carbon cycling processes such as soil CO2 flux, CO2 uptake by the dominant grasses, and aboveground net primary productivity (ANPP) were reduced, and ANPP was more responsive to soil moisture variability than to mean soil water content. Our results show that projected increases in rainfall variability can rapidly alter key carbon cycling processes and plant community composition, independent of changes in total precipitation.

1 aKnapp, Alan, K.1 aFay, P.A.1 aBlair, John, M.1 aCollins, Scott., L.1 aSmith, M.D.1 aCarlisle, J.D.1 aHarper, C.W.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K. uhttps://science.sciencemag.org/content/298/5601/220202614nas a2200277 4500008004100000245008000041210006900121300001300190490000700203520177300210653001201983653001701995653002102012653001202033653002202045100001402067700001902081700001702100700001502117700001902132700001602151700002002167700002002187700002402207856010502231 2001 eng d00aCarbon and water relations of juvenile Quercus species in tallgrass prairie0 aCarbon and water relations of juvenile Quercus species in tallgr a807 -8160 v123 aIn ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall-grass prairies of the central United States (relative to forests), we predicted that the grassland-forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall-grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above-ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 % higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland-forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C4 grasses.10aEcotone10aFacilitation10aforest expansion10aQuercus10atallgrass prairie1 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/carbon-and-water-relations-juvenile-quercus-species-tallgrass-prairie01482nas a2200313 4500008004100000245004900041210004800090300001300138490000800151520065800159100001600817700002000833700001500853700002400868700001500892700001600907700001600923700001600939700001400955700001400969700001600983700001500999700001501014700001301029700002201042700001501064700001301079856007601092 2001 eng d00aEcological forecasts: an emerging imperative0 aEcological forecasts an emerging imperative a657 -6600 v2933 aPlanning and decision-making can be improved by access to reliable forecasts of ecosystem state, ecosystem services, and natural capital. Availability of new data sets, together with progress in computation and statistics, will increase our ability to forecast ecosystem change. An agenda that would lead toward a capacity to produce, evaluate, and communicate forecasts of critical ecosystem services requires a process that engages scientists and decision-makers. Interdisciplinary linkages are necessary because of the climate and societal controls on ecosystems, the feedbacks involving social change, and the decision-making relevance of forecasts.1 aClark, J.S.1 aCarpenter, S.R.1 aBarber, M.1 aCollins, Scott., L.1 aDobson, A.1 aFoley, J.A.1 aLodge, D.M.1 aPascual, M.1 aPielke, R1 aPizer, W.1 aPringle, C.1 aReid, W.V.1 aRose, K.A.1 aSala, O.1 aSchlesinger, W.H.1 aWall, D.H.1 aWear, D. uhttp://knz.lternet.edu/content/ecological-forecasts-emerging-imperative02501nas a2200145 4500008004100000245009300041210006900134300001500203490000700218520194800225653002202173100001802195700002402213856011802237 2001 eng d00aFeedback loops in ecological hierarchies following urine deposition in tallgrass prairie0 aFeedback loops in ecological hierarchies following urine deposit a1319 -13290 v823 aAlthough theory predicts that large-scale factors will constrain small-scale interactions, the potential for small-scale events to impact large-scale patch structure is less clear. We examined experimentally the effects of urine deposition, a highly localized event, on small- and large-scale vegetation structure and spatial variation in tallgrass prairie. The response by vegetation to urine deposition may be mediated by grazing. Thus, we also determined the probability of urine patches serving as foci for grazing events by bison. Likelihood of bison grazing was much higher on vs. off urine patches, and grazed areas initiated on urine patches expanded well beyond the area of urine deposition. Abundance of four common graminoid species, and of all graminoids combined, increased on urine patches in ungrazed prairie, while the abundance of Andropogon gerardii and total graminoids decreased on urine patches in grazed prairie. The abundance of Aster ericoides, and all forbs combined, increased on urine patches in ungrazed, but not in grazed, prairie. Species richness and Shannon-Weiner diversity increased on urine patches in ungrazed prairie but were not affected by urine treatment in grazed prairie. Total spatial variance of graminoids increased relative to controls in response to urine treatment, grazing, and the combination of these treatments. For forbs, total variance increased marginally compared to controls only in response to urine treatment in ungrazed prairie. In combination, urine patches plus grazing produced unique large-scale patch structure compared to urine patches in ungrazed prairie. The most important impact of urine patches on community structure resulted from preferential grazing of urine patches by bison, which increases both the size and severity of the grazed area. Urine patches are thus an example of a small-scale perturbation that generates larger-scale patch structure in tallgrass prairie.10atallgrass prairie1 aSteinauer, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/feedback-loops-ecological-hierarchies-following-urine-deposition-tallgrass-prairie04557nas a2200265 4500008004100000245009100041210006900132260005100201300001100252520369800263653001703961653001903978653000903997653001504006653002004021653001204041100001604053700001604069700001604085700002404101700002004125700001504145700001504160856011604175 2001 eng d00aInteractions between fire and invasive plants in temperate grasslands of North America0 aInteractions between fire and invasive plants in temperate grass aTallahassee, FLbTall Timbers Research Station a40 -653 aA substantial number of invasive grasses, forbs and woody plants have invaded temperate grasslands in North America. Among the invading species are winter annuals, biennials, cool-season perennials, warm-season perennials, vines, shrubs, and trees. Many of these species have been deliberately introduced and widely planted; some are still used for range improvement, pastures, lawns, and as ornamentals, though many are listed as state or federal noxious weeds. Others have been greatly facilitated by widespread land disturbance. Historically, fire has been a major selective force in the evolution of temperate grasslands. Further, prescribed fire is commonly used as a method of ecological management for native grassland communities as well as in conjunction with restoration efforts. Within this context, it is important to understand how invasive species will interact with natural and prescribed fire regimes. In this paper, we consider what is known about how exotic species that invade temperate grasslands relate to fire. The primary issues addressed for each species are (1) Does fire appear to enhance colonization? (2) To what degree does fire affect the survival of plants? (3) Are plants that are burned able to regrow following fire and, if so, how rapidly can they recover? (4) How important is competition with native species to the response to fire? and (5) What effect does an invasive species have on the characteristics of the fire regime? For many species, results are preliminary, incomplete, or inconsistent among studies. For this reason, many of the conclusions drawn for individual species must be considered preliminary. Based on analyses of individual species, a conceptual framework is presented for considering how invasive plants may interact with fire when they invade an ecosystem. The major categories of influences are the native community, the fire regime, growth conditions for both invasive and native species, and influences that disturbances, human impacts, and landscape characteristics have had in the past and will have in the future. The examples considered in this paper provide support for a few, tentative generalizations. First, among our current worst invaders of temperate grasslands, adaptation to fire is quite variable. Some species are not well adapted to burning and can be easily eliminated; other species are better adapted but can still be eliminated if fire occurs during periods of particular vulnerability and/or at high frequency. There is a set of species that is extremely well adapted to fire and will not be eliminated through burning alone. Second, competitive interactions with native species play a crucial role in the success of nonnative invaders. In cases where differential burn responses between invasive and native species can be exploited, and adequate populations of native dominant species are present, fire can sometimes tip the competitive balance away from invasives. Third, there are a few invasive species that have exceptional attributes and for which there are no easy solutions. The ability of cheatgrass (Bromus tectorum) to enhance fire, the ability of Chinese tallow (Triadica sebifera) to suppress fire, and the ability of leafy spurge (Euphorbia esula) to resprout from repeated injury make the sespecies exceptional threats to native diversity. Finally, the available information for many invasive species is very incomplete, particularly with regard to how fire affects competitive interactions with the native community. There is much more we need to know if we are to consistently predict how invasive species will respond to fire and how burning can best be used to manage for natural diversity10aalien plants10aexotic species10afire10aGrasslands10ainvasive plants10aprairie1 aGrace, J.B.1 aSmith, M.D.1 aGrace, S.L.1 aCollins, Scott., L.1 aStohlgren, T.J.1 aGalley, K.1 aWilson, T. uhttp://knz.lternet.edu/content/interactions-between-fire-and-invasive-plants-temperate-grasslands-north-america00463nas a2200109 4500008004100000245008900041210006900130300001300199490000800212100002400220856010900244 2001 eng d00aLong-term research and the dynamics of bird populations and communities: an overview0 aLongterm research and the dynamics of bird populations and commu a583 -5880 v1181 aCollins, Scott., L. uhttp://knz.lternet.edu/content/long-term-research-and-dynamics-bird-populations-and-communities-overview01685nas a2200145 4500008004100000245008400041210006900125300001300194490000700207520116600214100002401380700001701404700001401421856010401435 2001 eng d00aA method to determine rate and pattern of variability in ecological communities0 amethod to determine rate and pattern of variability in ecologica a285 -2930 v913 aIt is well known that ecological communities are spatially and temporally dynamic. Quantifying temporal variability in ecological communities is challenging, however, especially for time-series data sets of less than 40 measurement intervals. In this paper, we describe a method to quantify temporal variability in multispecies communities over time frames of 10–40 measurement intervals. Our approach is a community-level extension of autocorrelation analysis, but we use Euclidean distance to measure similarity of community samples at increasing time lags rather than the correlation coefficient. Regressing Euclidean distances versus increasing time lags yields a measure of the rate and nature of community change over time. We demonstrate the method with empirical data sets from shortgrass steppe, old-field succession and zooplankton dynamics in lakes, and we investigate properties of the analysis using simulation models. Results indicate that time-lag analysis provides a useful quantitative measurement of the rate and pattern of temporal dynamics in communities over time frames that are too short for more traditional autocorrelation approaches.1 aCollins, Scott., L.1 aMichelli, F.1 aHartt, L. uhttp://knz.lternet.edu/content/method-determine-rate-and-pattern-variability-ecological-communities02886nas a2200289 4500008004100000245013100041210006900172300001300241490000600254520190600260653001902166653002402185653001502209653001802224653001902242653002302261653002702284653002702311653002102338653001802359100001402377700001902391700002002410700002002430700002402450856012202474 2000 eng d00aAltering rainfall timing and quantity in a mesic grassland ecosystem: Design and performance of rainfall manipulation shelters0 aAltering rainfall timing and quantity in a mesic grassland ecosy a308 -3190 v33 aGlobal climate change is predicted to alter growing season rainfall patterns, potentially reducing total amounts of growing season precipitation and redistributing rainfall into fewer but larger individual events. Such changes may affect numerous soil, plant, and ecosystem properties in grasslands and ultimately impact their productivity and biological diversity. Rainout shelters are useful tools for experimental manipulations of rainfall patterns, and permanent fixed-location shelters were established in 1997 to conduct the Rainfall Manipulation Plot study in a mesic tallgrass prairie ecosystem in northeastern Kansas. Twelve 9 x 14–m fixed-location rainfall manipulation shelters were constructed to impose factorial combinations of 30% reduced rainfall quantity and 50% greater interrainfall dry periods on 6 x 6–m plots, to examine how altered rainfall regimes may affect plant species composition, nutrient cycling, and above- and belowground plant growth dynamics. The shelters provided complete control of growing season rainfall patterns, whereas effects on photosynthetic photon flux density, nighttime net radiation, and soil temperature generally were comparable to other similar shelter designs. Soil and plant responses to the first growing season of rainfall manipulations (1998) suggested that the interval between rainfall events may be a primary driver in grassland ecosystem responses to altered rainfall patterns. Aboveground net primary productivity, soil CO2 flux, and flowering duration were reduced by the increased interrainfall intervals and were mostly unaffected by reduced rainfall quantity. The timing of rainfall events and resulting temporal patterns of soil moisture relative to critical times for microbial activity, biomass accumulation, plant life histories, and other ecological properties may regulate longer-term responses to altered rainfall patterns.10aClimate change10afloristic diversity10aGrasslands10aKonza Prairie10alife histories10along-term research10aNet primary production10aprecipitation patterns10arainout shelters10asoil moisture1 aFay, P.A.1 aCarlisle, J.D.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/altering-rainfall-timing-and-quantity-mesic-grassland-ecosystem-design-and-performance02942nas a2200193 4500008004100000245007800041210006900119300001300188490000800201520229000209653002302499653002402522653001602546653000902562653002202571653002502593100002402618856010602642 2000 eng d00aDisturbance frequency and community stability in native tallgrass prairie0 aDisturbance frequency and community stability in native tallgras a311 -3250 v1553 aEcological communities are spatially and temporally variable in response to a variety of biotic and abiotic forces. It is not always clear, however, if spatial and temporal variability leads to instability in communities. Instability may result from strong biotic interactions or from stochastic processes acting on small populations. I used 10–15 yr of annual data from the Konza Prairie Long‐Term Ecological Research site to examine whether plant, breeding bird, grasshopper, and small mammal communities in tallgrass prairie exhibit stability or directional change in response to different experimentally induced fire frequencies. Based on ordination and ANOVA, plant and grasshopper communities on annually burned sites differed significantly from plant and grasshopper communities on less frequently burned sites. Breeding birds and small mammals differed among sites as well, but these differences were not clearly related to disturbance frequency. A modified time series analysis indicated that plant communities were undergoing directional change (unstable) on all watersheds, regardless of fire frequency. Contrary to expectations, directional change was greatest on the annually burned sites and lowest on the infrequently burned sites. Unlike the plant communities, breeding bird, grasshopper, and small mammal communities were temporally stable, despite high‐compositional variability from 1 yr to the next. Stability among the consumer communities within these dynamic plant communities occurs because three‐dimensional vegetation structure does not change over time, despite changes in plant species composition. Evidence suggests that instability in the plant community results from strong biotic interactions among temporally persistent core species and stochastic dynamics among infrequent satellite species. Overall, community stability cannot be assessed if the pattern of temporal dynamics is unknown. Long‐term empirical studies of different taxa under different disturbance regimes are needed to determine over what time frames and spatial scales communities may be stable. Such studies are essential for the development of generalities regarding the relationship between disturbance frequency and community stability in terrestrial and aquatic systems.10aCommunity dynamics10acommunity stability10adisturbance10afire10atallgrass prairie10atemporal variability1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/disturbance-frequency-and-community-stability-native-tallgrass-prairie00419nas a2200133 4500008004100000245004500041210004500086300001300131490000700144100002000151700002400171700002000195856007000215 2000 eng d00aEcosystems as functional units in nature0 aEcosystems as functional units in nature a150 -1550 v141 aBlair, John, M.1 aCollins, Scott., L.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/ecosystems-functional-units-nature02456nas a2200157 4500008004100000245010200041210006900143300001300212490000700225520186600232100001402098700001902112700001602131700002402147856012702171 2000 eng d00aFertilization effects of species density and primary productivity in herbaceous plant communities0 aFertilization effects of species density and primary productivit a428 -4390 v893 aFertilization experiments in plant communities are often interpreted in the context of a hump-shaped relationship between species richness and productivity. We analyze results of fertilization experiments from seven terrestrial plant communities representing a productivity gradient (arctic and alpine tundra, two old-field habitats, desert, short- and tall-grass prairie) to determine if the response of species richness to experimentally increased productivity is consistent with the hump-shaped curve. In this analysis, we compared ratios of the mean response in nitrogen-fertilized plots to the mean in control plots for aboveground net primary productivity (ANPP) and species density (D; number of species per plot of fixed unit area). In general, ANPP increased and plant species density decreased following nitrogen addition, although considerable variation characterized the magnitude of response. We also analyzed a subset of the data limited to the longest running studies at each site (≥4 yr), and found that adding 9 to 13 g N m−2 yr−1 (the consistent amount used at all sites) increased ANPP in all communities by approximately 50% over control levels and reduced species density by approximately 30%. The magnitude of response of ANPP and species density to fertilization was independent of initial community productivity. There was as much variation in the magnitude of response among communities within sites as among sites, suggesting community-specific mechanisms of response. Based on these results, we argue that even long-term fertilization experiments are not good predictors of the relationship between species richness and productivity because they are relatively small-scale perturbations whereas the pattern of species richness over natural productivity gradients is influenced by long-term ecological and evolutionary processes.1 aGough, L.1 aOsenberg, C.W.1 aGross, K.L.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/fertilization-effects-species-density-and-primary-productivity-herbaceous-plant-communities00592nas a2200133 4500008004100000245014400041210006900185300001500254490000700269100001700276700001400293700002400307856012700331 1999 eng d00aThe core-satellite species hypothesis provides a theoretical basis for Grimes classification of dominant subordinate, and transient species0 acoresatellite species hypothesis provides a theoretical basis fo a1064 -10670 v871 aGibson, D.J.1 aEly, J.S.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/core-satellite-species-hypothesis-provides-theoretical-basis-grimes-classification-dominant00565nas a2200181 4500008004100000245006700041210006300108300001100171490000700182100002000189700002000209700001900229700002400248700001900272700001800291700001600309856005800325 1999 eng d00aThe keystone role of bison in North American tallgrass prairie0 akeystone role of bison in North American tallgrass prairie a39 -500 v491 aKnapp, Alan, K.1 aBlair, John, M.1 aBriggs, J., M.1 aCollins, Scott., L.1 aHartnett, D.C.1 aJohnson, L.C.1 aTowne, E.G. uhttp://www.jstor.org/stable/10.1525/bisi.1999.49.1.3900648nas a2200217 4500008004100000245003900041210003900080260003800119300001300157653002200170100001800192700001800210700001400228700002000242700001600262700002000278700001900298700001900317700002400336856007000360 1998 eng d00aAnimal populations and communities0 aAnimal populations and communities aNew YorkbOxford University Press a113 -13910atallgrass prairie1 aKaufman, D.W.1 aKaufman, G.A.1 aFay, P.A.1 aZimmerman, J.L.1 aEvans, E.W.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/animal-populations-and-communities00677nas a2200229 4500008004100000245003800041210003800079260003800117300001300155653002200168100001700190700001500207700002000222700001900242700001800261700001700279700002000296700001900316700001900335700002400354856006900378 1998 eng d00aBelowground biology and processes0 aBelowground biology and processes aNew YorkbOxford University Press a244 -26410atallgrass prairie1 aRice, C., W.1 aTodd, T.C.1 aBlair, John, M.1 aSeastedt, T.R.1 aRamundo, R.A.1 aWilson, G.T.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/belowground-biology-and-processes00779nas a2200205 4500008004100000245012500041210006900166260003800235300001300273653002200286100001900308700001700327700001800344700002000362700002000382700001900402700001900421700002400440856010900464 1998 eng d00aClimate change, elevated CO2 and predictive modeling: Past and future climate change scenarios for the tallgrass prairie0 aClimate change elevated CO2 and predictive modeling Past and fut aNew YorkbOxford University Press a283 -30010atallgrass prairie1 aSeastedt, T.R.1 aHayden, B.P.1 aOwensby, C.E.1 aKnapp, Alan, K.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland%20dynamics%20ch16.pdf00664nas a2200181 4500008004100000245007300041210006900114260003800183300001300221653002200234100002400256700002000280700002000300700001900320700001900339700002400358856010000382 1998 eng d00aDisturbance, diversity and species interactions in tallgrass prairie0 aDisturbance diversity and species interactions in tallgrass prai aNew YorkbOxford University Press a140 -15610atallgrass prairie1 aCollins, Scott., L.1 aSteinauer, E.M.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/disturbance-diversity-and-species-interactions-tallgrass-prairie00620nas a2200205 4500008004100000245004000041210004000081260003800121300001300159653002200172100001800194700001400212700001800226700002000244700002000264700001900284700001900303700002400322856006800346 1998 eng d00aDiversity of terrestrial macrofauna0 aDiversity of terrestrial macrofauna aNew YorkbOxford University Press a101 -11210atallgrass prairie1 aKaufman, D.W.1 aFay, P.A.1 aKaufman, G.A.1 aZimmerman, J.L.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/diversity-terrestrial-macrofauna00721nas a2200205 4500008004100000245007200041210006700113260003800180300001300218653002200231100002400253700002000277700001900297700001900316700002000335700001900355700001900374700002400393856009800417 1998 eng d00aThe dynamic tallgrass prairie: Synthesis and research opportunities0 adynamic tallgrass prairie Synthesis and research opportunities aNew YorkbOxford University Press a301 -31510atallgrass prairie1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aHartnett, D.C.1 aBriggs, J., M.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/dynamic-tallgrass-prairie-synthesis-and-research-opportunities00628nas a2200169 4500008004100000245007800041210006900119260003800188300001100226653002200237100001800259700002000277700001900297700001900316700002400335856009900359 1998 eng d00aThe flora of Konza Prairie: A historical review and contemporary patterns0 aflora of Konza Prairie A historical review and contemporary patt aNew YorkbOxford University Press a69 -8010atallgrass prairie1 aFreeman, C.C.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/flora-konza-prairie-historical-review-and-contemporary-patterns00522nas a2200169 4500008004100000245003900041210003900080260003800119300001100157653002200168100001700190700002000207700001900227700001900246700002400265856006300289 1998 eng d00aGeomorphology of the Konza Prairie0 aGeomorphology of the Konza Prairie aNew YorkbOxford University Press a35 -4710atallgrass prairie1 aOviatt, C.G.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/geomorphology-konza-prairie00600nam a2200157 4500008004100000245007500041210006900116260003800185300001300223653002200236100002000258700001900278700001900297700002400316856010200340 1998 eng d00aGrassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie0 aGrassland Dynamics LongTerm Ecological Research in Tallgrass Pra aNew YorkbOxford University Press a364 -36410atallgrass prairie1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/grassland-dynamics-long-term-ecological-research-tallgrass-prairie00634nas a2200181 4500008004100000245006400041210006200105260003800167300001000205653002200215100002000237700001900257700002000276700001900296700001900315700002400334856009400358 1998 eng d00aGrasslands, Konza Prairie and long-term ecological Research0 aGrasslands Konza Prairie and longterm ecological Research aNew YorkbOxford University Press a3 -1510atallgrass prairie1 aKnapp, Alan, K.1 aSeastedt, T.R.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/grasslands-konza-prairie-and-long-term-ecological-research00617nas a2200205 4500008004100000245003600041210003600077260003800113300001300151653002200164100001500186700002300201700002000224700001800244700002000262700001900282700001900301700002400320856006700344 1998 eng d00aHydrology and aquatic chemistry0 aHydrology and aquatic chemistry aNew YorkbOxford University Press a159 -17610atallgrass prairie1 aGray, L.J.1 aMacpherson, G., L.1 aKoelliker, J.K.1 aDodds, W., K.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/hydrology-and-aquatic-chemistry00738nas a2200217 4500008004100000245007500041210006900116260003800185300001300223653002200236100001900258700001700277700001700294700001800311700001100329700002000340700001900360700001900379700002400398856009800422 1998 eng d00aA landscape perspective of patterns and processes in tallgrass prairie0 alandscape perspective of patterns and processes in tallgrass pra aNew YorkbOxford University Press a265 -27910atallgrass prairie1 aBriggs, J., M.1 aNellis, M.D.1 aTurner, C.L.1 aHenebry, G.M.1 aSu, H.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/landscape-perspective-patterns-and-processes-tallgrass-prairie01416nas a2200181 4500008004100000245007800041210006900119300001300188490000800201520080000209653002201009100002401031700002001055700001901075700002001094700002001114856010001134 1998 eng d00aModulation of diversity by grazing and mowing in native tallgrass prairie0 aModulation of diversity by grazing and mowing in native tallgras a745 -7470 v2803 aSpecies diversity has declined in ecosystems worldwide as a result of habitat fragmentation, eutrophication, and land-use change. If such decline is to be halted ecological mechanisms that restore or maintain biodiversity are needed. Two long-term field experiments were performed in native grassland to assess the effects of fire, nitrogen addition, and grazing or mowing on plant species diversity. In one experiment, richness declined on burned and fertilized treatments, whereas mowing maintained diversity under these conditions. In the second experiment, loss of species diversity due to frequent burning was reversed by bison, a keystone herbivore in North American grasslands. Thus, mowing or the reestablishment of grazing in anthropogenically stressed grasslands enhanced biodiversity.10atallgrass prairie1 aCollins, Scott., L.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aBlair, John, M.1 aSteinauer, E.M. uhttp://knz.lternet.edu/content/modulation-diversity-grazing-and-mowing-native-tallgrass-prairie00742nas a2200205 4500008004100000245008500041210006900126260003800195300001300233653002200246100002000268700001900288700002000307700001700327700002000344700001900364700001900383700002400402856011000426 1998 eng d00aPatterns and controls of aboveground net primary production in tallgrass prairie0 aPatterns and controls of aboveground net primary production in t aNew YorkbOxford University Press a193 -22110atallgrass prairie1 aKnapp, Alan, K.1 aBriggs, J., M.1 aBlair, John, M.1 aTurner, C.L.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/patterns-and-controls-aboveground-net-primary-production-tallgrass-prairie00577nas a2200181 4500008004100000245004600041210004500087260003800132300001200170653002200182100001900204700001400223700002000237700001900257700001900276700002400295856007600319 1998 eng d00aPlant populations: Patterns and processes0 aPlant populations Patterns and processes aNew YorkbOxford University Press a81 -10010atallgrass prairie1 aHartnett, D.C.1 aFay, P.A.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/plant-populations-patterns-and-processes00615nas a2200169 4500008004100000245006300041210006300104260003800167300001100205653002200216100001700238700002000255700001900275700001900294700002400313856010800337 1998 eng d00aRegional climate and the distribution of tallgrass prairie0 aRegional climate and the distribution of tallgrass prairie aNew YorkbOxford University Press a19 -3410atallgrass prairie1 aHayden, B.P.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland%20dynamics%20ch2.pdf00576nas a2200205 4500008004100000245002500041210002500066260003800091300001100129653002200140100001700162700001700179700001500196700002100211700002000232700001900252700001900271700002400290856005600314 1998 eng d00aSoils and soil biota0 aSoils and soil biota aNew YorkbOxford University Press a48 -6610atallgrass prairie1 aRansom, M.D.1 aRice, C., W.1 aTodd, T.C.1 aWehmueller, W.A.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/soils-and-soil-biota00589nas a2200181 4500008004100000245005000041210005000091260003800141300001300179653002200192100001500214700001800229700002000247700001900267700001900286700002400305856007800329 1998 eng d00aStructure and dynamics of aquatic communities0 aStructure and dynamics of aquatic communities aNew YorkbOxford University Press a177 -18910atallgrass prairie1 aGray, L.J.1 aDodds, W., K.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/structure-and-dynamics-aquatic-communities00666nas a2200205 4500008004100000245005400041210005400095260003800149300001300187653002200200100002000222700001900242700001700261700001800278700002000296700001900316700001900335700002400354856008200378 1998 eng d00aTerrestrial nutrient cycling in tallgrass prairie0 aTerrestrial nutrient cycling in tallgrass prairie aNew YorkbOxford University Press a222 -24310atallgrass prairie1 aBlair, John, M.1 aSeastedt, T.R.1 aRice, C., W.1 aRamundo, R.A.1 aKnapp, Alan, K.1 aBriggs, J., M.1 aHartnett, D.C.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/terrestrial-nutrient-cycling-tallgrass-prairie04795nas a2200133 4500008004100000245009700041210006900138300001300207490000600220520427600226100002404502700001604526856011904542 1997 eng d00aEffects of organismal and distance scaling on analysis of species distribution and abundance0 aEffects of organismal and distance scaling on analysis of specie a543 -5510 v73 aAs communities and populations become increasingly fragmented, much theoretical and some empirical research has focused on the dynamics of metapopulations. Many metapopulation models describe dynamics among populations in a region, yet the scale of the region to which different models apply often is undefined. Because the spatial scale is undefined, testing predictions and assumptions of these models is problematic. Our goal is to present two scaling concepts relevant to these models, distance scaling and organismal scaling, and to apply these scaling notions to patterns of species distribution. To determine distance effects, we analyzed patterns of distribution of four taxonomic groups in tallgrass prairie (grasshoppers, small mammals, vascular plants, and breeding birds) at two spatial scales. To asses organismal effects, we held spatial scale constant and we compared patterns of distribution and abundance among these taxonomic groups. Using long—term data from Konza Prairie, Kansas, there were significant differences in the pattern of distribution of grasshoppers, small mammals, vascular plants, and breeding birds within a single spatial scale. The number of core species (species occupying >90% of the sites in a region) of plants and birds was less than the number of satellite species (those occupying <10% of the sites in a region). The opposite was true for grasshoppers and small mammals. All four distribution patterns were significantly nonrandom, but only grasshoppers and small mammals were significantly bimodal at this scale. Plants and birds were unimodal. The patterns of distribution within these taxonomic groups at two spatial scales were significantly different as well. In all cases, the percentage of species in the core group declined, and the percentage of species in the satellite group increased as spatial scale increased. These results demonstrate the difficulty of testing theoretical models with only one taxonomic group at a single spatial scale. One should not accept or reject a model until the spatial domains of organismal and distance scaling have been properly evaluated. As communities and populations become increasingly fragmented, much theoretical and some empirical research has focused on the dynamics of metapopulations. Many metapopulation models describe dynamics among populations in a region, yet the scale of the “region” to which different models apply often is undefined. Because the spatial scale is undefined, testing predictions and assumptions of these models is problematic. Our goal is to present two scaling concepts relevant to these models, distance scaling and organismal scaling, and to apply these scaling notions to patterns of species distribution. To determine distance effects, we analyzed patterns of distribution of four taxonomic groups in tallgrass prairie (grasshoppers, small mammals, vascular plants, and breeding birds) at two spatial scales. To assess organismal effects, we held spatial scale constant and we compared patterns of distribution and abundance among these taxonomic groups. Using long-term data from Konza Prairie, Kansas, there were significant differences in the pattern of distribution of grasshoppers, small mammals, vascular plants, and breeding birds within a single spatial scale. The number of core species (species occupying >90% of the sites in a region) of plants and birds was less than the number of satellite species (those occupying <10% of the sites in a region). The opposite was true for grasshoppers and small mammals. All four distribution patterns were significantly non-random, but only grasshoppers and small mammals were significantly bimodal at this scale. Plants and birds were unimodal. The patterns of distribution within these taxonomic groups at two spatial scales were significantly different as well. In all cases, the percentage of species in the core group declined, and the percentage of species in the satellite group increased as spatial scale increased. These results demonstrate the difficulty of testing theoretical models with only one taxonomic group at a single spatial scale. One should not accept or reject a model until the spatial domains of organismal and distance scaling have been properly evaluated.1 aCollins, Scott., L.1 aGlenn, S.M. uhttp://knz.lternet.edu/content/effects-organismal-and-distance-scaling-analysis-species-distribution-and-abundance02212nas a2200133 4500008004100000245008700041210006900128300001100197490000700208520170600215100001901921700002401940856011401964 1997 eng d00aGradient models, gradient analysis and hierarchical structure in plant communities0 aGradient models gradient analysis and hierarchical structure in  a23 -300 v783 aTwo general models of plant community structure, the community-unit and the continuum, have dominated the thinking of American community ecologists. Hypotheses derived from these and other models of plant community structure rarely have been tested, however. Traditionally, analyses of gradient structure have focused primarily on whether or not the boundaries of species response curves are clustered, which does not provide a complete picture of gradient structure. In this study, we statistically analyzed three characteristics of plant community structure along gradients (1) pattern of boundaries of species distributions, (2) pattern of modes of species response curves, and (3) whether or not species distributions exhibit hierarchical structure. In combination, these characteristics yield eight different models of vegetation structure along gradients. To determine if vegetation corresponds to any of these models, we sampled species composition using belt transects of contiguous quadrats in a total of 42 wetland sites in Minnesota and the southern Great Plains, USA. Boundaries of species distributions were clustered in 10 of 42 cases, modes of species response curves were clustered in 19 of 42 cases, and species distributions exhibited hierarchical structure in all 42 cases. Results varied between sites. Overall, four models of community structure were supported. None of the sites sampled supported the models often associated with the continuum or the community-unit. These results confirmed the need to explore alternative models of gradient structure, and suggested that more than one model of vegetation structure may be needed to represent community structure along gradients.1 aHoagland, B.W.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/gradient-models-gradient-analysis-and-hierarchical-structure-plant-communities01376nas a2200133 4500008004100000245008800041210006900129300001300198490000700211520094300218100002401161700001601185856004101201 1997 eng d00aIntermediate disturbance and its relationship to within-and between-patch structure0 aIntermediate disturbance and its relationship to withinand betwe a103 -1100 v213 aThe intermediate disturbance hypothesis has been the focus of considerable analysis in terrestrial and aquatic systems. This model predicts that species diversity will be highest at intermediate frequencies of disturbance. Despite numerous theoretical and empirical analyses, the utility of the model is still the subject of intense debate. Rather than developing restrictive time and space constraints on application, we suggest that the model may best be used as a generalizable framework for testing hypotheses in both aquatic and terrestrial systems. In addition, we believe that the model may be applied to both within- and between-patch scales. Finally, we propose an empirical model in which disturbance is an extinction causing event, and post-disturbance succession is modeled based on the dynamics of immigration and extinction. Such a model can incorporate a variety of patterns in species diversity in response to disturbance.1 aCollins, Scott., L.1 aGlenn, S.M. uhttp://www.jstor.org/stable/2405453001366nas a2200157 4500008004100000245009500041210006900136260003000205300001000235520077300245100001701018700002401035700001601059700001701075856011601092 1997 eng d00aLandscape gradients and habitat structure in native grasslands of the central great plains0 aLandscape gradients and habitat structure in native grasslands o aNew YorkbSpringer-Verlag a3 -193 aHabitat variables have a powerful influence on the distribution and abundance of organisms, and many organisms directly affect the physical structure of their local environment. These interactions produce a complex feedback system that drives community dynamics. This scenario is particularly true in grasslands where the effects of “keystone engineers,” such as the North American bison (Bison bison), have a tremendous influence on ecosystem structure and function (Collins and Benning 1996). This interplay between organisms and habitat structure in grasslands occurs within a climatic regime that varies dramatically from one year to the next. In addition, the relative influence of different habitat variables changes at different spatial and temporal scales.1 aVinton, M.A.1 aCollins, Scott., L.1 aKnopf, F.L.1 aSamson, F.B. uhttp://knz.lternet.edu/content/landscape-gradients-and-habitat-structure-native-grasslands-central-great-plains00685nas a2200157 4500008004100000245004200041210004100083260003300124300001100157653002200168100002000190700002400210700001600234700001700250856026000267 1996 eng d00aPrairie ecology-the tallgrass prairie0 aPrairie ecologythe tallgrass prairie aWashington, DCbIsland Press a39 -5210atallgrass prairie1 aSteinauer, E.M.1 aCollins, Scott., L.1 aKnopf, F.L.1 aSamson, F.B. uhttps://books.google.com/books?hl=en&lr=&id=ZlHRjU2EDLQC&oi=fnd&pg=PA39&dq=%22Prairie%2Becology-the%2Btallgrass%2Bprairie%22+Steinauer&ots=7TE04D0yxT&sig=B4UaGusICyHJqjiwWNTFkCdrE_0#v=onepage&q=%22Prairie%2Becology-the%2Btallgrass%2Bprairie%22%20Steinauer00476nas a2200133 4500008004100000245005800041210005800099260002900157300001300186100002400199700001800223700001500241856008600256 1996 eng d00aSpatial and temporal patterns in functional diversity0 aSpatial and temporal patterns in functional diversity bBlackwell Science London a253 -2801 aCollins, Scott., L.1 aBenning, T.L.1 aGaston, K. uhttp://knz.lternet.edu/content/spatial-and-temporal-patterns-functional-diversity01399nas a2200133 4500008004100000245008200041210006900123300001300192490000700205520090500212100001301117700002401130856011101154 1996 eng d00aTrophic interactions and plant species richness along a productivity gradient0 aTrophic interactions and plant species richness along a producti a603 -6070 v763 aWe analyzed the interactive effects of trophic structure and disturbance on species diversity of plant communities along a productivity gradient by merging the intermediate disturbance hypothesis with a simple three-trophic-level predator-prey model. In two-trophic-level systems, i.e. without carnivores, the model produces a unimodal, hump-shaped pattern of species richness, which is consistent with patterns predicted from other models. If carnivores are included, trophic cascades produce a bimodal pattern of species richness over the productivity gradient. We have found no appropriate data sets in the literature with which to assess the validity of our model. We thus offer the model as an alternative hypothesis to be tested regarding plant species richness in productivity gradients, and as a reminder of the importance of trophic structure for patterns and processes in plant communities.1 aMoen, J.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/trophic-interactions-and-plant-species-richness-along-productivity-gradient01837nas a2200133 4500008004100000245008600041210006900127300001500196490000700211520133400218100002001552700002401572856010701596 1995 eng d00aEffects of urine deposition on small\-scale patch structure in prairie vegetation0 aEffects of urine deposition on smallscale patch structure in pra a1195 -12050 v763 aLarge grazing mammals contribute to the species diversity of grasslands via direct and indirect effects of defoliation and urine deposition. We examined the influence of one and two applications of simulated bovine urine on vegetation structure on (1) tallgrass prairie burned either every 2 or 4 yr at Konza Prairie Research Natural Area (KPRNA), Kansas, and (2) unburned sandhills prairie at the Niobrara Valley Preserve, Nebraska. We also examined the influence of urine and the clipping of graminoids on an annually burned site at KPRNA. Plant abundance in general increased on urine patches but the response appeared dependent on litter accumulation. C"4 grasses increased at the annual burn and Niobrara sites where litter levels were low. C"3 forbs increased at the 2- and 4-yr burn sites where litter levels were high. Urine treatment significantly affected community composition at all but the 2-yr burn site. Alpha-diversity decreased on urine patches at the annual and 4-yr burn sites but increased on urine patches at the Niobrara site. Beta-diversity increased on urine patches at the annual burn and Niobrara site but decreased on urine patches at the 4-yr burn site. The clipping of graminoids at the annual burn site reduced both @a- and @b-diversity and graminoid abundance while forb abundance was not affected.1 aSteinauer, E.M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/effects-urine-deposition-small-scale-patch-structure-prairie-vegetation02542nas a2200145 4500008004100000245011700041210006900158300001300227490000700240520196500247100002402212700001602236700001702252856012702269 1995 eng d00aExperimental analysis of intermediate disturbance and initial floristic composition: decoupling cause and effect0 aExperimental analysis of intermediate disturbance and initial fl a486 -4920 v763 aThe intermediate disturbance hypothesis predicts that richness will be highest in communities with moderate levels of disturbance and at intermediate time spans following disturbance. This model was proposed as a nonequilibrium explanation of species richness in tropical forests and coral reefs. A second model of succession, initial floristic composition, states that nearly all species, including late seral species, are present at the start of succession. This leads to the prediction that richness should be highest immediately following disturbance. We tested these predictions using plant species composition data from two long—term field experiments in North American tallgrass prairie vegetation. In contrast to one prediction of the intermediate disturbance hypothesis, there was a significant monotonic decline in species richness with increasing disturbance frequency, with no evidence of an optimum, in both field experiments. Species composition on an annually burned site was a subset of that of infrequently burned sites. The average number of species per quadrat and the number of grass, forb, and annual species were lowest on annually burned sites compared to unburned sites and sites burned once every 4 yr. The second prediction of the intermediate disturbance hypothesis, however, was supported. Richness reached a maximum at an intermediate time interval since the last disturbance. This contradicts the prediction from the initial floristic composition model of succession. These results also suggest that the two predictions of the intermediate disturbance hypothesis are independent and unrelated. We propose that this may be explained by uncoupling the effects of disturbance as a single, relatively discrete event from system response to disturbance. From this perspective, disturbance becomes an extinction—causing event in these grasslands, where recovery following disturbance is a balance between immigration and extinction.1 aCollins, Scott., L.1 aGlenn, S.M.1 aGibson, D.J. uhttp://knz.lternet.edu/content/experimental-analysis-intermediate-disturbance-and-initial-floristic-composition-decoupling02895nas a2200241 4500008004100000245009700041210006900138300001300207490000700220520209400227653001402321653002202335653002402357653002302381653001802404653001202422653002502434100001502459700002402474700001602498700001602514856012302530 1995 eng d00aFine-scale spatial organization of tallgrass prairie vegetation along a topographic gradient0 aFinescale spatial organization of tallgrass prairie vegetation a a169 -1840 v303 aFine-scale spatial patterns of native tallgrass prairie vegetation were studied on Konza Prairie, Kansas, USA. Three sites, upland, slope, and lowland, were sampled in an ungrazed watershed. Presence of vascular plant species was recorded in two 25.6 m long transects of contiguous 5×5 cm micro-quadrats on each topographic position. Spatial patterns of species and functional groups were analyzed by information theory models ofJuhász-Nagy. Within-community variability of coexistence was expressed by the diversity and spatial dependence of local species combinations. Considerable diversity in the local coexistence of species was found on each site. Upland and hillside communities were richer and more diverse in species combinations than lowland. Spatial scale effected coexistence relationships. The maxima of information theory estimates varied between 15 and 30 cm. There was no trend in the variation of characteristic scales along the topographical gradient. Above 10 m, all sites tended to be homogeneous. The analysis of spatial associations revealed that variability in the local coexistence of species was strongly constrained in all topographic positions. Overall spatial association of species was the lowest on lowland. The characteristic scales of maximum association were between 1.2 m and 3 m at all sites. The maxima of information theory estimates for the functional group-based data appeared at smaller plot sizes than for the species based analyses. Only weak spatial associations were detected among the functional groups indicating that individuals of functional groups coexist well at small scales, and form combinations close to random expectations. The length of transects did not effect the relative associations. Strong positive correlations were found between the number of components (species or functional groups) and the maxima, of information theory models suggesting that richness is a good predictor of within-community coexistence relations. However, there was no relationship between richness and the characteristic scales of community patterns.10adiversity10aFunctional groups10aGrassland community10ainformation theory10aKonza Prairie10aScaling10aSpatial associations1 aBartha, S.1 aCollins, Scott., L.1 aGlenn, S.M.1 aKertesz, M. uhttp://knz.lternet.edu/content/fine-scale-spatial-organization-tallgrass-prairie-vegetation-along-topographic-gradient00476nas a2200145 4500008004100000245004700041210004700088260002800135300001300163100002400176700001600200700001900216700001700235856007800252 1995 eng d00aGrassland ecosystem and landscape dynamics0 aGrassland ecosystem and landscape dynamics bOxford University Press a128 -1561 aCollins, Scott., L.1 aGlenn, S.M.1 aJoern, Anthony1 aKeeler, K.K. uhttp://knz.lternet.edu/content/grassland-ecosystem-and-landscape-dynamics00351nas a2200109 4500008004100000245004700041210004300088300001100131490000700142100002400149856006800173 1995 eng d00aThe measurement of stability in grasslands0 ameasurement of stability in grasslands a95 -960 v101 aCollins, Scott., L. uhttp://knz.lternet.edu/content/measurement-stability-grasslands00982nas a2200133 4500008004100000245005900041210005900100300001100159490000600170520054300176100001800719700002400737856008700761 1994 eng d00aExperimental manipulation of natural plant communities0 aExperimental manipulation of natural plant communities a94 -980 v93 aAttempts to elucidate the factors controlling the structure of plant communities have relied increasingly on field experiments. This is a powerful approach for testing theoretical predictions that offers important advantages over observational and comparative studies. However, field experiments suffer from intrinsic difficulties as well as more-easily remediable limitations. Recent progress has been made by new approaches including the use of multifactor experiments, and the development and dissemination of better statistical tools.1 aGurevitch, J.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/experimental-manipulation-natural-plant-communities00481nas a2200121 4500008004100000245007300041210006900114300001300183653002200196100001900218700002400237856009800261 1994 eng d00aUsing remote sensing to determine heterogeneity in tallgrass prairie0 aUsing remote sensing to determine heterogeneity in tallgrass pra a113 -11910atallgrass prairie1 aBriggs, J., M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/using-remote-sensing-determine-heterogeneity-tallgrass-prairie02501nas a2200181 4500008004100000245008300041210006900124300001300193490000600206520186400212653002402076653002002100653002302120653002802143100001602171700002402187856010802211 1993 eng d00aExperimental analysis of patch dynamics in tallgrass prairie plant communities0 aExperimental analysis of patch dynamics in tallgrass prairie pla a157 -1620 v43 aPrevious research has indicated that patch structure at small spatial scales (<100m2) in tallgrass prairies was defined by a diverse array of infrequent species because dominant species occurred in all samples at this scale. Also, patch structure was not significantly different from that derived from random species associations. Based on these results, we hypothesized that remo val of a dominant species would have no effect on patch structure in these prairies. We tested this hypothesis by removing a dominant grass, Schizachyrium scoparium (Poaceae), from half of each of four 10 m × 10 m study blocks, and comparing differences in patch structure between control and removal halves before and after removal. The minimum resolution in our study was 1 m2. Patches of similar species composition were defined by cluster analysis of presence/absence data and cover data. Patch sizes ranged from 1 to 34 m2. Following the removal of S. scoparium there was an overall increase in the number of species in the removal half of each block compared to pre-treatment levels. However, the number of patch types and number of spatially mapped groups, based on presence/absence or cover data, did not change between control and removal plots after the removal of S. scoparium. This supports the hypothesis that removal of a large, dominant species would have no effect on patch structure at this scale of resolution in these prairies. Thus, patch structure, as defined here, is an emergent property in these grasslands that is not predictable from changes in species composition. This property of stochastic patch structure results from interactions of processes operating at scales both larger and smaller than our scale of resolution. Stochastic models may provide a reasonable approach to modelling small-scale patch dynamics in tallgrass prairie communities.10aGrassland community10aPatch structure10aRemoval experiment10aSchizachyrium scoparium1 aGlenn, S.M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/experimental-analysis-patch-dynamics-tallgrass-prairie-plant-communities02275nas a2200193 4500008004100000245003900041210003500080300001300115490000600128520173000134653002401864653002001888653002201908653002701930100002401957700001601981700001801997856006602015 1993 eng d00aThe hierarchical continuum concept0 ahierarchical continuum concept a149 -1560 v43 aTwo general models have been proposed to explain the structure of the plant community: the community-unit model of Clements and the continuum model of Whittaker and Curtis, the latter based on Gleason's individualistic distribution of species. It is generally assumed that most ecologists now accept the continuum model. Empirical evidence suggests, however, that the continuum in its current form does not fully describe the observed patterns of vegetation along environmental gradients. In this paper, we introduce the hierarchical continuum as a general concept to represent dynamic community structure along regional spatial gradients. The hierarchical continuum is derived from a combination of the individualistic distribution of species, hierarchical assemblage structure, and the core-satellite species hypothesis. The hierarchical continuum concept predicts that the distribution of species across sites in a region will be polymodal, which reflects hierarchical structure, and that the distribution and abundance of species within and between sites will be spatially and temporally dynamic. Regional distribution of plant species in North American tallgrass prairie, southeastern flood-plain hardwood forests, northern upland hardwood forests, and boreal forests were either bimodal or polymodal as predicted by the hierarchical continuum concept. Species in tallgrass prairie were spatially and temporally dynamic with an average turnover of 8–9 species per 50 m2 yr1. In addition, the hierarchical continuum concept predicts the potential for fractal (self-similar) patterns of community structure, and provides a framework for testable hypotheses concerning species distributions along environmental gradients.10acommunity structure10aContinuum model10aGradient analysis10aHierarchical structure1 aCollins, Scott., L.1 aGlenn, S.M.1 aRoberts, D.W. uhttp://knz.lternet.edu/content/hierarchical-continuum-concept00475nas a2200133 4500008004100000245006600041210006500107300001300172490000600185100001800191700002400209700001500233856009300248 1993 eng d00aMechanisms and processes in vegetation dynamics: Introduction0 aMechanisms and processes in vegetation dynamics Introduction a146 -1480 v41 aAgnew, A.D.Q.1 aCollins, Scott., L.1 aMaarel, E. uhttp://knz.lternet.edu/content/mechanisms-and-processes-vegetation-dynamics-introduction00570nas a2200145 4500008004100000245009600041210006900137300001300206490000600219653002200225100001600247700002400263700001700287856012000304 1992 eng d00aDisturbances in tallgrass prairie: local versus regional effects on community heterogeneity0 aDisturbances in tallgrass prairie local versus regional effects  a243 -2520 v710atallgrass prairie1 aGlenn, S.M.1 aCollins, Scott., L.1 aGibson, D.J. uhttp://knz.lternet.edu/content/disturbances-tallgrass-prairie-local-versus-regional-effects-community-heterogeneity02072nas a2200145 4500008004100000245009900041210006900140300001300209490000700222520153300229653000901762100001601771700002401787856011501811 1992 eng d00aEffects of scale and disturbance on rates of immigration and extinction of species in prairies0 aEffects of scale and disturbance on rates of immigration and ext a273 -2800 v633 a

Relationships between local annual immigration and extinction rate of plant species and total species richness were determined from long-term data in permanent plots in tallgrass and shortgrass prairies in Kansas. Combining plots resulted in higher equilibrium numbers of species as predicted from immigration and extinction rates. Immigration and extinction rates also increased with scale. Extinction rates are higher because the regional scale supports more rare species which, in turn, have high probabilities of extinction. We also tested the hypothesis that extinction rates would be higher on burned versus unburned grasslands, and that immigration rates would be higher on grazed versus ungrazed grasslands. Extinction rates were positively correlated with the number of species at a site, and this relationship was not altered by burning or grazing. Immigration rates were variable, but were sometimes positively correlated with growing season precipitation. Immigration rates decreased in years sites were burned. Therefore, after fire, the number of species going locally extinct was still dependent on earlier species richness, but the number of species added to the site was reduced. Variances in immigration and extinction rates were high, therefore, confident predictions regarding the effects of burning or grazing regimes on species richness could not be made. Variance in rates of immigration and extinction results in a range of values within which the equilibrium number of species fluctuates randomly

10afire1 aGlenn, S.M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/effects-scale-and-disturbance-rates-immigration-and-extinction-species-prairies03048nas a2200133 4500008004100000245007900041210006900120300001500189490000700204520255000211653002202761100002402783856010702807 1992 eng d00aFire frequency and community heterogeneity in tallgrass prairie vegetation0 aFire frequency and community heterogeneity in tallgrass prairie  a2001 -20060 v733 a

Few studies have directly addressed the effects of disturbance on spatial and temporal heterogeneity. Spatial hererogeneity is the degree of dissimilarity in species composition from one point to another in a community, wheras temporal heterogeneity is compositional change within a site over time. The purposes of this study were to determine 1) if a quadratic relationship exists between within-site heterogenity and disturbance frequency as predicted by the intermediated disturbance hypothesis (IDH), 2)if disturbed and undistubed sites have similar heterogeneity as implied by the disturbance heterogeneity hypothesis (DHM), and whether or not these results differed with scale, and 3)if there is a relationship between spatial and temporal heterogeneity as implied by the DHM. Analyses were based on plant species composition data collected over 9 yr in quadrats permanently located in experimental management units subjected to different burning frequencies at Konza Prairie Research Natual Area, Kansas, USA. The relationship between disturbance frequency and within-site heterogeneity was opposie that predicted by the IDH. Heterogeneity was lowest at intermediate disturbance frequencies. Heterogeneity in anually burned prairie was lower than in unburned prairie and prairies burned once every 4 yr in contrast to predictions of the DHM. However, this relationship did not hold at larger spatial scales. There was a positive relationship between disturbance frequency and within-site heterogenity was opposite that predicted by the IDH. Heterogenity was lowest at intermediate disturbance frequencies. Heterogeneity in annually burned prairie was lower than in unburned prairie and prairies burned once every year in contrast to predictions of the DHM. However, this relationship did not hold at larger spatial scales. There was a positive relationship between within-site spatial and temporal heterogeneity on annually burned sites, sites burned once every 4 yr, and nearly so on sites burned every other year. Within-site heterogeneity was negatively correlated with cover of Andropogon gerardii, and positively correlated with total richness and species diversity. Studies of variation, in addition to averages, will increase our ability to predict patterns of species distribution and abundance within and between communities in response to disturbance. Key words: Andropogon gerardii, fire, grassland vegetation, intermediate disturbance hypothesis, Konza Prairie, spatial heterogeneity, species density, species diversity

10atallgrass prairie1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/fire-frequency-and-community-heterogeneity-tallgrass-prairie-vegetation00507nas a2200121 4500008004100000245009500041210006900136300001300205490000700218100002400225700001600249856012000265 1991 eng d00aImportance of spatial and temporal dynamics in species regional abundance and distribution0 aImportance of spatial and temporal dynamics in species regional  a654 -6640 v721 aCollins, Scott., L.1 aGlenn, S.M. uhttp://knz.lternet.edu/content/importance-spatial-and-temporal-dynamics-species-regional-abundance-and-distribution00591nas a2200157 4500008004100000245007000041210006900111260004500180300001100225653002200236100002400258700001700282700002400299700001800323856009200341 1990 eng d00aEffects of fire on plant community structure in tallgrass prairie0 aEffects of fire on plant community structure in tallgrass prairi aNorman, OKbUniversity of Oklahoma Press a81 -9810atallgrass prairie1 aCollins, Scott., L.1 aGibson, D.J.1 aCollins, Scott., L.1 aWallace, L.L. uhttp://knz.lternet.edu/content/effects-fire-plant-community-structure-tallgrass-prairie00523nam a2200157 4500008004100000245004500041210004500086260004500131300001000176653002200186100002400208700001800232700002400250700001800274856007300292 1990 eng d00aFire in North American tallgrass prairie0 aFire in North American tallgrass prairie aNorman, OKbUniversity of Oklahoma Press a175 -10atallgrass prairie1 aCollins, Scott., L.1 aWallace, L.L.1 aCollins, Scott., L.1 aWallace, L.L. uhttp://knz.lternet.edu/content/fire-north-american-tallgrass-prairie00480nas a2200121 4500008004100000245008200041210006900123300001300192490000800205100002400213700001600237856010500253 1990 eng d00aA hierarchical analysis of species abundance patterns in grassland vegetation0 ahierarchical analysis of species abundance patterns in grassland a633 -6480 v1351 aCollins, Scott., L.1 aGlenn, S.M. uhttp://knz.lternet.edu/content/hierarchical-analysis-species-abundance-patterns-grassland-vegetation00590nas a2200157 4500008004100000245007300041210006900114260004500183300001200228653002200240100001900262700001800281700002400299700001800323856009100341 1990 eng d00aThe influence of fire on belowground processes of tallgrass prairies0 ainfluence of fire on belowground processes of tallgrass prairies aNorman, OKbUniversity of Oklahoma Press a99 -11710atallgrass prairie1 aSeastedt, T.R.1 aRamundo, R.A.1 aCollins, Scott., L.1 aWallace, L.L. uhttp://knz.lternet.edu/content/influence-fire-belowground-processes-tallgrass-prairies00578nas a2200145 4500008004100000245007900041210006900120260004500189300000900234653002200243100002400265700002400289700001800313856010100331 1990 eng d00aIntroduction: Fire as a natural distubance in tallgrass prairie ecosystems0 aIntroduction Fire as a natural distubance in tallgrass prairie e aNorman, OKbUniversity of Oklahoma Press a3 -710atallgrass prairie1 aCollins, Scott., L.1 aCollins, Scott., L.1 aWallace, L.L. uhttp://knz.lternet.edu/content/introduction-fire-natural-distubance-tallgrass-prairie-ecosystems02160nas a2200145 4500008004100000245007300041210006900114300001300183490000700196520165200203653002201855100001601877700002401893856009701917 1990 eng d00aPatch structure in tallgrass prairies: dynamics of satellite species0 aPatch structure in tallgrass prairies dynamics of satellite spec a229 -2360 v573 a

Space in tallgrass prairie communities is dominated by a few core species. A large number of less abundant, satellite species occupy the remaining space. These satellite species define vegetation patches that vary withinn and between growing seasons. In order to determine if patch structure was random we established five permanent 100-m2 blocks in undisturbed tallgrass prairie in Oklahoma and Kansas. Presence of core and satellite species in each m2 was sampled over one or two growing seasons. Patch types were defined by cluster analysis. Characteristics of patch structure included number of patch types, patch type diversity, patch composition, number of spatial groups, group size, and fractal dimension of the spatial groups. We generated simulated data sets with random species associations, in which we quantified patch structure. Actual patch structure, defined mainly by satellite species, was not significanly different from simulated patch structure, except that simulated patches were more fragmented. Therefore, processes that affect species associations may not be important controls of patch structure of satellite species within the spatial and temporal scale of this analysis. Because there was some degree of spatial autocorrelation in patch structure, dispersal processes may have significant effects on patch structure at this scale. In order to understand grassland community dynamics, we propose that satellite species should be modelled using stochastic models constrained by core species dynamics. This approach may be applicable to any community with major components operating at different hierarchical levels

10atallgrass prairie1 aGlenn, S.M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/patch-structure-tallgrass-prairies-dynamics-satellite-species01365nas a2200181 4500008004100000245003800041210003800079260004600117300001100163520083700174653000901011100001801020700001601038700001801054700002401072700001801096856006901114 1990 eng d00aSmall mammals and grassland fires0 aSmall mammals and grassland fires aNorman, OKbUniversity of Okalahoma Press a46 -803 a

For study of fire effects, the general null hypothesis is that fire will have no impact on the population density of individual animal species. Any species that fails to change numerically due to fire would be classified as a fire-neutral species. Alternatively, a population that could exhibit either a positive or negative numerical response to fire. Such species we classify as fire-positive or fire-negative species, respectively. Most early work on animals and fire was aimed at describing these general population responses. However, understanding the structure and function of grasslands demands that we know patterns of population changes from prefire through a multiyear, post-fire period, rather than simply ascertaining whether species are fire- positve, fire-negative, or fire-neutral over a short postfire period

10afire1 aKaufman, D.W.1 aFinck, E.J.1 aKaufman, G.A.1 aCollins, Scott., L.1 aWallace, L.L. uhttp://knz.lternet.edu/content/small-mammals-and-grassland-fires