@article {6292, title = {Drought-tolerant grassland species are generally more resistant to competition}, journal = {Journal of Ecology}, year = {In Press}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.14243}, url = {https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.14243}, author = {Mount, Hailey E. and M. D. Smith and Alan K. Knapp and Griffin-Nolan, R.J. and Collins, Scott L. and Atkins, David H. and Stears, Alice E. and Laughlin, Daniel C.} } @article {6165, title = {Stronger fertilization effects on aboveground versus belowground plant properties across nine U.S. grasslands}, journal = {Ecology}, volume = {104}, year = {2023}, pages = {e3891}, abstract = {

Increased nutrient inputs due to anthropogenic activity are expected to increase primary productivity across terrestrial ecosystems, but changes in allocation aboveground versus belowground with nutrient addition have different implications for soil carbon (C) storage. Thus, given that roots are major contributors to soil C storage, understanding belowground net primary productivity (BNPP) and biomass responses to changes in nutrient availability is essential to predicting carbon\–climate feedbacks in the context of interacting global environmental changes. To address this knowledge gap, we tested whether a decade of nitrogen (N) and phosphorus (P) fertilization consistently influenced aboveground and belowground biomass and productivity at nine grassland sites spanning a wide range of climatic and edaphic conditions in the continental United States. Fertilization effects were strong aboveground, with both N and P addition stimulating aboveground biomass at nearly all sites (by 30\% and 36\%, respectively, on average). P addition consistently increased root production (by 15\% on average), whereas other belowground responses to fertilization were more variable, ranging from positive to negative across sites. Site-specific responses to P were not predicted by the measured covariates. Atmospheric N deposition mediated the effect of N fertilization on root biomass and turnover. Specifically, atmospheric N deposition was positively correlated with root turnover rates, and this relationship was amplified with N addition. Nitrogen addition increased root biomass at sites with low N deposition but decreased it at sites with high N deposition. Overall, these results suggest that the effects of nutrient supply on belowground plant properties are context dependent, particularly with regard to background N supply rates, demonstrating that site conditions must be considered when predicting how grassland ecosystems will respond to increased nutrient loading from anthropogenic activity.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecy.3891}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.3891}, author = {Keller, Adrienne B. and Walter, Christopher A. and Blumenthal, Dana M. and Borer, Elizabeth T. and Collins, Scott L. and DeLancey, Lang C. and Fay, Philip A. and Hofmockel, Kirsten S. and Knops, Johannes M. H. and Leakey, Andrew D. B. and Mayes, Melanie A. and Seabloom, Eric W. and Hobbie, Sarah E.} } @article {6163, title = {Do trade-offs govern plant species{\textquoteright} responses to different global change treatments?}, journal = {Ecology}, volume = {103}, year = {2022}, pages = {e3626}, keywords = {LTER-KNZ}, issn = {0012-9658}, doi = {10.1002/ecy.3626}, url = {https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3626}, author = {Langley, J. Adam and Grman, Emily and K.R. Wilcox and M.L. Avolio and Kimberly J. Komatsu and Collins, Scott L. and Koerner, S.E. and M. D. Smith and Baldwin, Andrew H. and Bowman, William and Chiariello, Nona and Eskelinen, Anu and Harmens, Harry and Hovenden, Mark and Klanderud, Kari and McCulley, Rebecca L. and Onipchenko, Vladimir G. and Robinson, Clare H. and K.N. Suding} } @article {6133, title = {Linking changes in species composition and biomass in a globally distributed grassland experiment}, journal = {Ecology Letters}, volume = {25}, year = {2022}, pages = {2699-2712}, keywords = {LTER-KNZ}, doi = {10.1111/ele.14126}, url = {https://onlinelibrary.wiley.com/doi/10.1111/ele.14126}, author = {Ladouceur, Emma and Blowes, Shane A. and Chase, Jonathan M. and Clark, Adam T. and Garbowski, Magda and Alberti, Juan and Arnillas, Carlos Alberto and Bakker, Jonathan D. and Barrio, Isabel C. and Bharath, Siddharth and Borer, Elizabeth T. and Brudvig, Lars A. and Cadotte, Marc W. and Chen, Qingqing and Collins, Scott L. and Dickman, Christopher R. and Donohue, Ian and Du, Guozhen and Ebeling, Anne and Eisenhauer, Nico and Fay, Philip A. and Hagenah, Nicole and Hautier, Yann and Jentsch, Anke and J{\'o}nsd{\'o}ttir, Ingibj{\"o}rg S. and Kimberly J. Komatsu and MacDougall, Andrew and Martina, Jason P. and Moore, Joslin L. and Morgan, John W. and Peri, Pablo L. and Power, ~A. and Ren, Zhengwei and Risch, Anita C. and Roscher, Christiane and Schuchardt, ~A. and Seabloom, Eric W. and Stevens, Carly J. and Veen, G.F. (Ciska) and Virtanen, Risto and Wardle, Glenda M. and Wilfahrt, Peter A. and Harpole, W. Stanley} } @article {KNZ002043, title = {Fire frequency, state change and hysteresis in tallgrass prairie}, journal = {Ecology Letters}, volume = {24}, year = {2021}, pages = {636-647}, abstract = {

Hysteresis is a fundamental characteristic of alternative stable state theory, yet evidence of hysteresis is rare. In mesic grasslands, fire frequency regulates transition from grass- to shrub-dominated system states. It is uncertain, however, if increasing fire frequency can reverse shrub expansion, or if grass-shrub dynamics exhibit hysteresis. We implemented annual burning in two infrequently burned grasslands and ceased burning in two grasslands burned annually. With annual fires, grassland composition converged on that of long-term annually burned vegetation due to rapid recovery of grass cover, although shrubs persisted. When annual burning ceased, shrub cover increased, but community composition did not converge with a long-term infrequently burned reference site because of stochastic and lagged dispersal by shrubs, reflecting hysteresis. Our results demonstrated that annual burning can slow, but not reverse, shrub encroachment. In addition, reversing fire frequencies resulted in hysteresis because vegetation trajectories from grassland to shrubland differed from those of shrubland to grassland.

}, keywords = {LTER-KNZ}, doi = {10.1111/ele.13676}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/ele.13676}, author = {Collins, Scott L. and Nippert, J.B. and Blair, J. M. and J. M. Briggs and Blackmore, P. and Ratajczak, Zak} } @article {6003, title = {Why coordinated distributed experiments should go global}, journal = {BioScience}, volume = {71}, year = {2021}, pages = {918 - 927}, keywords = {LTER-KNZ}, doi = {10.1093/biosci/biab033}, url = {https://academic.oup.com/bioscience/article/71/9/918/6259352}, author = {Yahdjian, Laura and Sala, Osvaldo E and Pi{\~N}Eiro-Guerra, Juan Manuel and Alan K. Knapp and Collins, Scott L. and Phillips, Richard P and M. D. Smith} } @article {KNZ002010, title = {Soil heterogeneity increases plant diversity after twenty years of manipulation during grassland restoration}, journal = {Ecological Applications}, volume = {30}, year = {2020}, pages = {e02014}, abstract = {

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.

}, keywords = {LTER-KNZ}, author = {S.G. Baer and T. Adams and Scott, D.A. and John M. Blair and Scott. L. Collins} } @article {KNZ001943, title = {The combined effects of an extreme heatwave and wildfire on tallgrass prairie vegetation}, journal = {Journal of Vegetation Science}, volume = {30}, year = {2019}, pages = {687 - 697}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/jvs.12750}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12750}, author = {Z. Ratajczak and Churchill, Amber C. and Ladwig, Laura M. and Taylor, Jeff H. and Scott. L. Collins} } @article {KNZ001953, title = {A comprehensive approach to analyzing community dynamics using rank abundance curves}, journal = {Ecosphere}, volume = {10}, year = {2019}, pages = {e02881}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecs2.2881}, url = {https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecs2.2881}, author = {M.L. Avolio and Carroll, I. and Scott. L. Collins and Houseman, Gregory R. and Hallett, L.M. and Isbell, F.L. and Koerner, S.E. and Kimberly J. Komatsu and M.D. Smith and K.R. Wilcox} } @article {KNZ001965, title = {Global change effects on plant communities are magnified by time and the number of global change factors imposed}, journal = {Proceedings of the National Academy of Sciences}, volume = {116}, year = {2019}, pages = {17867-17873}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1073/pnas.1819027116}, url = {https://www.pnas.org/content/early/2019/08/14/1819027116}, author = {Kimberly J. Komatsu and M.L. Avolio and Lemoine, Nathan P. and Isbell, Forest and Grman, Emily and Houseman, Gregory R. and Koerner, Sally E. and Johnson, D.S. and K.R. Wilcox and Juha M. Alatalo and Anderson, J.P. and Aerts, R. and S.G. Baer and Baldwin, Andrew H. and Bates, J. and Beierkuhnlein, C. and Belote, R.T. and John M. Blair and Bloor, J.M.G. and Bohlen, P.J. and Edward W. Bork and Elizabeth H. Boughton and W.D. Bowman and Britton, Andrea J. and Cahill, James F. and Chaneton, Enrique J. and Chiariello, N.R. and Cheng, Jimin. and Scott. L. Collins and Cornelissen, J.H.C. and G. Du and Eskelinen, Anu and Firn, Jennifer and Foster, B. and Gough, L. and Gross, K. and Hallett, L.M. and Han, X. and Harmens, H. and Hovenden, M.J. and Jagerbrand, A. and Jentsch, A. and Kern, Christel and Klanderud, Kari and Alan K. Knapp and Kreyling, Juergen and Li, W. and Luo, Yiqi and McCulley, R.L. and McLaren, Jennie R. and Megonigal, Patrick and J.W. Morgan and Onipchenko, Vladimir and Pennings, S.C. and Prev{\'e}y, J.S. and Price, Jodi N. and P.B. Reich and Robinson, Clare H. and Russell, L.F. and Sala, O.E. and Seabloom, E.W. and M.D. Smith and Soudzilovskaia, Nadejda A. and Souza, Lara and K.N. Suding and Suttle, B.K. and Svejcar, T. and Tilman, David and Tognetti, P. and Turkington, R. and White, S. and Xu, Zhuwen and Yahdjian, L. and Yu, Q. and Zhang, Pengfei and Zhang, Yunhai} } @article {KNZ001983, title = {Shifts in plant functional composition following long-term drought in grasslands}, journal = {Journal of Ecology}, volume = {107}, year = {2019}, pages = {2133 - 2148}, abstract = {

\ 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.

}, keywords = {LTER-KNZ, ANPP, Climate change, community weighted traits, Drought, Functional diversity, plant functional traits}, doi = {10.1111/1365-2745.13252}, url = {https://besjournals.onlinelibrary.wiley.com/doi/10.1111/1365-2745.13252}, author = {Griffin-Nolan, Robert J. and D.M. Blumenthal and Scott. L. Collins and Farkas, Timothy E. and Hoffman, Ava M. and Mueller, Kevin E. and Ocheltree, Troy W. and M.D. Smith and Whitney, Kenneth D. and Alan K. Knapp}, editor = {Jones, Holly} } @article {KNZ001985, title = {Soil net nitrogen mineralisation across global grasslands}, journal = {Nature Communications}, volume = {10}, year = {2019}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1038/s41467-019-12948-2}, url = {http://www.nature.com/articles/s41467-019-12948-2}, author = {Risch, A.C. and Zimmermann, S. and Ochoa-Hueso, R. and sch{\"u}tz, M. and Frey, B. and Firn, J. L. and Fay, P. A. and Hagedorn, F. and E.T. Borer and Seabloom, E. W. and Harpole, W. S. and Knops, J. M. H. and McCulley, R. L. and Broadbent, A. A. D. and Stevens, C. J. and Silveira, M. L. and P. Adler and B{\'a}ez, S. and L.A. Biederman and John M. Blair and Brown, C. S. and Caldeira, M. C. and Scott. L. Collins and Daleo, P. and di Virgilio, A. and Ebeling, A. and Eisenhauer, N. and Esch, E. and Eskelinen, A. and Hagenah, N. and Hautier, Y. and Kirkman, K. P. and MacDougall, A. S. and Joslin L. Moore and Power, S. A. and Prober, S. M. and Roscher, C. and Sankaran, M. and Siebert, J. and Speziale, K. L. and Tognetti, P. M. and Virtanen, R. and Yahdjian, L. and Moser, B.} } @article {KNZ001888, title = {Change in dominance determines herbivore effects on plant biodiversity}, journal = {Nature Ecology and Evolution}, volume = {2}, year = {2018}, pages = {1925-1932}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {https://doi.org/10.1038/s41559-018-0696-y}, url = {https://www.nature.com/articles/s41559-018-0696-y$\#$article-info}, author = {Koerner, S.E. and M.D. Smith and Burkepile, D.E. and N.P. Hanan and M.L. Avolio and Scott. L. Collins and Alan K. Knapp and N.P. Lemoine and E.J. Forrestel and S. Eby and D.I. Thompson and G. Aguado-Santacruz and J.P. Anderson and Anderson, M. and A. Angassa and S. Bagchi and E.S. Bakker and Bastin, Gary and L.E. Baur and K.H. Beard and E.A. Beever and P.J. Bohlen and Elizabeth H. Boughton and Canestro, Don and Cesa, Ariela and Chaneton, Enrique and Cheng, Jimin and C.M. D{\textquoteright}Antonio and C. Deleglise and Fadiala. Demb{\'e}l{\'e} and Josh. Dorrough and David. J. Eldridge and Barbara. Fernandez-Going and Silvia. Fern{\'a}ndez-Lugo and Lauchlan. H. Fraser and Bill. Freedman and Gonzalo. Garc{\'\i}a-Salgado and Jacob. R. Goheen and Liang. Guo and Sean. Husheer and Moussa. Karemb{\'e} and Johannes. M. H. Knops and Tineke. Kraaij and Andrew. Kulmatiski and Minna-Maarit. Kyt{\"o}viita and Felipe. Lezama and Gregory. Loucougaray and Alejandro. Loydi, Dan G. Milchunas, and Dan.G. Milchunas, and Suzanne. J. Milton and J.W. Morgan and Claire. Moxham and Kyle. C. Nehring and Han. Olff and Todd. M. Palmer and Salvador. Rebollo and Corinna. Riginos and Anita. C. Risch and Marta Rueda and Mahesh. Sankaran and Takehiro. Sasaki and Kathryn. A. Schoenecker and Nick. L. Schultz and Martin. Sch{\"u}tz and Angelika. Schwabe and Frances. Siebert and Christian. Smit and Karen. A. Stahlheber and Christian. Storm and Dustin. J. Strong and Jishuai. Su and Yadugiri. V. Tiruvaimozhi and Claudia. Tyler and James. Val and Martijn. L. Vandegehuchte and Kari. E. Veblen and Lance. T. Vermeire and David. Ward and Jianshuang. Wu and Truman. P. Young and Qiang. Yu and Tamara. Jane. Zelikova} } @article {KNZ001886, title = {Drought consistently alters the composition of soil fungal and bacterial communities in grasslands from two continents}, journal = {Global Change Biology}, volume = {24}, year = {2018}, pages = {2818 - 2827}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.2018.24.issue-710.1111/gcb.14113}, url = {http://doi.wiley.com/10.1111/gcb.2018.24.issue-7}, author = {Ochoa-Hueso, Ra{\'u}l and Scott. L. Collins and Delgado-Baquerizo, Manuel and Hamonts, Kelly and Pockman, William T. and Sinsabaugh, Robert L. and M.D. Smith and Alan K. Knapp and Power, Sally A.} } @article {KNZ001885, title = {Legacy effects of a regional drought on aboveground net primary production in six central US grasslands}, journal = {Plant Ecology}, volume = {219}, year = {2018}, pages = {505 - 515}, abstract = {

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.

}, keywords = {LTER-KNZ}, issn = {1385-0237}, doi = {10.1007/s11258-018-0813-7}, url = {http://link.springer.com/10.1007/s11258-018-0813-7.pdf}, author = {Griffin-Nolan, Robert J. and Carroll, Charles J. W. and Denton, Elsie M. and Johnston, Melissa K. and Scott. L. Collins and M.D. Smith and Alan K. Knapp} } @article {KNZ001884, title = {Regional grassland productivity responses to precipitation during multiyear above- and below-average rainfall periods}, journal = {Global Change Biology}, volume = {24}, year = {2018}, pages = {1935 - 1951}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.2018.24.issue-510.1111/gcb.14024}, url = {https://www.ncbi.nlm.nih.gov/pubmed/29265568}, author = {Petrie, Matthew D. and Peters, Debra P. C. and Yao, Jin and John M. Blair and Burruss, Nathan D. and Scott. L. Collins and Derner, Justin D. and Gherardi, Laureano A. and Hendrickson, John R. and Sala, Osvaldo E. and Starks, Patrick J. and Steiner, Jean L.} } @article {KNZ001882, title = {Spatial heterogeneity in species composition constrains plant community responses to herbivory and fertilisation}, journal = {Ecology Letters}, volume = {21}, year = {2018}, pages = {1364 -1371}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/ele.13102}, url = {https://onlinelibrary.wiley.com/doi/pdf/10.1111/ele.13102}, author = {Hodapp, Dorothee and E.T. Borer and Harpole, W. Stanley and Lind, Eric M. and Seabloom, Eric W. and P. Adler and J. Alberti and Arnillas, Carlos A. and J.D. Bakker and L.A. Biederman and Cadotte, Marc and Cleland, Elsa E. and Scott. L. Collins and Fay, Philip A. and Firn, Jennifer and Hagenah, Nicole and Hautier, Yann and Iribarne, Oscar and Knops, Johannes M. H. and McCulley, Rebecca L. and MacDougall, Andrew and Joslin L. Moore and J.W. Morgan and Mortensen, Brent and Kimberly J. La Pierre and Risch, Anita C. and Sch{\"u}tz, Martin and Peri, Pablo and Stevens, Carly J. and Wright, Justin and Hillebrand, Helmut}, editor = {Gurevitch, Jessica} } @article {KNZ001811, title = {Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments}, journal = {Global Change Biology}, volume = {23}, year = {2017}, month = {4376-4385}, abstract = {

Climatic changes are altering Earth\&$\#$39;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.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.13706}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13706}, author = {K.R. Wilcox and Shi, Zheng and Gherardi, Laureano A. and Lemoine, Nathan P. and Koerner, Sally E. and Hoover, David L. and Bork, Edward and Byrne, Kerry M. and Cahill, James and Scott. L. Collins and Evans, Sarah and Gilgen, Anna K. and Holub, Petr and Jiang, Lifen and Alan K. Knapp and LeCain, Daniel and Liang, Junyi and Garcia-Palacios, Pablo and Pe{\~n}uelas, Josep and Pockman, William T. and M.D. Smith and Sun, Shanghua and White, Shannon R. and Yahdjian, Laura and Zhu, Kai and Luo, Yiqi} } @article {KNZ001842, title = {Asynchrony among local communities stabilises ecosystem function of metacommunities}, journal = {Ecology Letters}, year = {2017}, abstract = {

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.

}, keywords = {LTER-KNZ, Alpha diversity, alpha variability, beta diversity, Biodiversity, CoRRE data base, patchiness, Plant communities, Primary productivity, species synchrony}, doi = {10.1111/ele.12861}, url = {http://onlinelibrary.wiley.com/doi/10.1111/ele.12861/epdf}, author = {K.R. Wilcox and Tredennick, Andrew T. and Koerner, Sally E. and Grman, Emily and Hallett, Lauren M. and M.L. Avolio and Kimberly J. La Pierre and Houseman, Gregory R. and Isbell, Forest and Johnson, David Samuel and Juha M. Alatalo and Baldwin, Andrew H. and Edward W. Bork and Elizabeth H. Boughton and W.D. Bowman and Britton, Andrea J. and Cahill, James F. and Scott. L. Collins and G. Du and Eskelinen, Anu and Gough, Laura and Jentsch, Anke and Kern, Christel and Klanderud, Kari and Alan K. Knapp and Kreyling, Juergen and Luo, Yiqi and McLaren, Jennie R. and Megonigal, Patrick and Onipchenko, Vladimir and Prev{\'e}y, Janet and Price, Jodi N. and Robinson, Clare H. and Sala, Osvaldo E. and M.D. Smith and Soudzilovskaia, Nadejda A. and Souza, Lara and Tilman, David and White, Shannon R. and Xu, Zhuwen and Yahdjian, Laura and Yu, Qiang and Zhang, Pengfei and Zhang, Yunhai}, editor = {Gurevitch, Jessica} } @article {KNZ001794, title = {Changes in spatial variance during a grassland to shrubland state transition}, journal = {Journal Ecology}, volume = {105}, year = {2017}, pages = {750-760}, abstract = {
  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.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.12696}, url = {https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.12696}, author = {Z. Ratajczak and D{\textquoteright}Odorico, P.D. and Jesse B. Nippert and Scott. L. Collins and N. Brunsell and Ravi, S.} } @article {KNZ001808, title = {The interactive effects of press/pulse intensity and duration on regime shifts at multiple scales}, journal = {Ecological Monographs}, volume = {87}, year = {2017}, pages = {198-218}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1002/ecm.1249}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1002/ecm.1249}, author = {Z. Ratajczak and D{\textquoteright}Odorico, Paolo and Scott. L. Collins and B.T. Bestelmeyer and Isbell, F.L. and Jesse B. Nippert} } @article {KNZ001783, title = {Pushing precipitation to the extremes in distributed experiments: recommendations for simulating wet and dry years}, journal = {Global Change Biology}, volume = {23}, year = {2017}, pages = {1774-1782}, abstract = {

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\&$\#$39;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.

}, keywords = {LTER-KNZ}, doi = {10.1111/gcb.13504}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13504}, author = {Alan K. Knapp and M.L. Avolio and Beier, C. and Carroll, C.J.W. and Scott. L. Collins and Dukes, J.S. and Fraser, L.H. and Griffin-Nolan, R.J. and Hoover, D.L. and Jentsch, A. and Loik, M.E. and Phillips, R.P. and Post, A.K. and Sala, O.E. and Slette, I.J. and Yahdjian, L. and M.D. Smith} } @article {KNZ001830, title = {Species reordering, not changes in richness, drives long-term dynamics in grassland communities}, journal = {Ecology Letters}, volume = {20}, year = {2017}, pages = {1565}, chapter = {1556}, abstract = {

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.

}, keywords = {LTER-KNZ, Community dynamics, desert grassland, desert shrubland, fire; species reordering, Species richness, tallgrass prairie}, doi = {10.1111/ele.12864}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/ele.12864}, author = {Jones, Sydney K. and Ripplinger, Julie and Scott. L. Collins}, editor = {Coulson, Tim} } @article {KNZ001744, title = {Altered rainfall patterns increase forb abundance and richness in native tallgrass prairie}, journal = {Scientific Reports}, year = {2016}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1038/srep20120}, url = {https://www.nature.com/articles/srep20120}, author = {Jones, Sydney K. and Scott. L. Collins and John M. Blair and M.D. Smith and Alan K. Knapp} } @article {KNZ001745, title = {codyn: An R package of community dynamics metrics}, journal = {Methods in Ecology and Evolution}, volume = {7}, year = {2016}, pages = {1146{\textendash}1151}, abstract = {
  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.
}, keywords = {LTER-KNZ}, doi = {10.1111/2041-210X.12569}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.12569}, author = {Hallett, L.M. and Jones, S.K. and MacDonald, A.A.M. and Jones, M.B. and Flynn, D.F.B. and Ripplinger, J. and Slaughter, P. and Gries, C. and Scott. L. Collins} } @article {KNZ001743, title = {Environmental heterogeneity has a weak effect on diversity during community assembly in tallgrass prairie}, journal = {Ecological Monographs}, volume = {86}, year = {2016}, pages = {94 - 106}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/15-0888.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/15-0888.1}, author = {S.G. Baer and John M. Blair and Scott. L. Collins} } @article {KNZ001733, title = {Nutrient additions cause divergence of tallgrass prairie plant communities resulting in loss of ecosystem stability}, journal = {Journal of Ecology}, volume = {104}, year = {2016}, pages = {1478-1487}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.12610}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12610}, author = {Koerner, S.E. and M.L. Avolio and Kimberly J. La Pierre and K.R. Wilcox and M.D. Smith and Scott. L. Collins} } @article {KNZ001709, title = {The sensitivity of carbon exchanges in Great Plains grasslands to precipitation variability}, journal = {Journal of Geophysical Research: Biogeosciences}, volume = {121}, year = {2016}, pages = {280-294}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1002/2015JG003205}, url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JG003205}, author = {Petrie, M.D. and N. Brunsell and Vargas, R. and Scott. L. Collins and Flanagan, L.B. and Hanan, N.P. and Litvak, M.E. and Suyker, A.E.} } @article {KNZ001748, title = {Shared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands}, journal = {BioScience}, volume = {66}, year = {2016}, pages = {666 - 682}, type = {Journal Articles}, abstract = {

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.

}, keywords = {LTER-KNZ, Aboveground net primary productivity, fire, grassland, Grazing, plant community}, doi = {10.1093/biosci/biw077}, url = {https://academic.oup.com/bioscience/article/66/8/666/2464141}, author = {M.D. Smith and Alan K. Knapp and Scott. L. Collins and Burkepile, D.E. and Kirkman, K.P. and Koerner, S.E. and Thompson, D.I. and John M. Blair and Burns, C.E. and Eby, S. and Forrestel, E.J. and Fynn, R.W.S. and Govender, N. and Hagenah, N. and Hoover, D.L. and K.R. Wilcox} } @article {KNZ001698, title = {Anthropogenic nitrogen deposition predicts local grassland primary production worldwide}, journal = {Ecology}, volume = {96}, year = {2015}, pages = {1459 -1465}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {http://dx.doi.org/10.1890/14-1902.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/14-1902.1}, author = {Stevens, C.J. and Lind, E.M. and Hautier, Y. and Harpole, W.S. and E.T. Borer and Hobbie, S. and Seabloom, E.Q. and L. Ladwig and J.D. Bakker and Chu, C. and Scott. L. Collins and Davies, K.F. and Firn, J. and Hillebrand, H. and Kimberly J. La Pierre and MacDougall, A.S. and Melbourne, B.A. and McCulley, R.L. and J.W. Morgan and Orrock, J.L. and Prober, S.M. and A. Risch and Schultz, M. and Wragg, P.D.} } @article {KNZ001631, title = {Differential sensitivity to regional-scale drought in six central US grasslands}, journal = {Oecologia}, volume = {177}, year = {2015}, pages = {949 -957}, abstract = {

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.

}, keywords = {LTER-KNZ, Climate change, Functional diversity, Long-term ecological research, Precipitation, Primary production}, doi = {10.1007/s00442-015-3233-6}, url = {https://link.springer.com/article/10.1007\%2Fs00442-015-3233-6}, author = {Alan K. Knapp and Carroll, C.J.W. and Denton, E.M. and Kimberly J. La Pierre and Scott. L. Collins and M.D. Smith} } @article {KNZ001689, title = {Global environmental change and the nature of aboveground net primary productivity responses: insights from long-term experiments}, journal = {Oecologia}, volume = {177}, year = {2015}, month = {Jan-04-2015}, pages = {935 - 947}, abstract = {

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.

}, keywords = {LTER-KNZ, Aboveground productivity, Hierarchical response framework (HRF), Long-Term Ecological Research (LTER) Network, Nutrient addition, Precipitation manipulation}, issn = {0029-8549}, doi = {10.1007/s00442-015-3230-9}, url = {https://link.springer.com/article/10.1007\%2Fs00442-015-3230-9}, author = {M.D. Smith and Kimberly J. La Pierre and Scott. L. Collins and Alan K. Knapp and Gross, K.L. and Barrett, J.E. and Frey, S.D. and Gough, L. and Miller, R.J. and Morris, J.T. and Rustad, L.E. and Yarie, J.} } @article {KNZ001788, title = {Grassland productivity limited by multiple nutrients}, journal = {Nature Plants}, volume = {1}, year = {2015}, pages = {15080}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1038/nplants.2015.80}, url = {https://www.nature.com/articles/nplants201580}, author = {Fay, P.A. and Prober, S.M. and Harpole, W.S. and Knops, J.M.H. and J.D. Bakker and E.T. Borer and Lind, E.M. and MacDougall, A.S. and Seabloom, E.W. and Wragg, P.D. and P. Adler and D.M. Blumenthal and Buckley, Y.M. and Chu, C. and Cleland, E.E. and Scott. L. Collins and Davies, K.F. and G. Du and Feng, X. and Firn, J. and Gruner, D.S. and Hagenah, N. and Hautier, Y. and Heckman, R.W. and Jin, V.L. and Kirkman, K.P. and Klein, J. and L. Ladwig and Li, Q. and McCulley, R.L. and Melbourne, B.A. and Mitchell, C.E. and Joslin L. Moore and J.W. Morgan and A. Risch and sch{\"u}tz, M. and Stevens, C.J. and Wedin, D.A. and Yang, L.H.} } @article {KNZ001589, title = {Biotic mechanisms of community stability shift along a precipitation gradient}, journal = {Ecology}, volume = {95}, year = {2014}, pages = {1693 -1700}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/13-0895.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-0895.1}, author = {Hallett, L.M. and Hsu, J.S. and Cleland, E.E. and Scott. L. Collins and Dickson, T.L. and Farrer, E.C. and Gherardi, L.A. and Gross, K.L. and Hobbs, R.J. and Turnbull, L. and K.N. Suding} } @article {KNZ001667, title = {Changes in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above-ground productivity in a tallgrass prairie}, journal = {Journal of Ecology}, volume = {102}, year = {2014}, pages = {1649 -1660}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/1365-2745.12312}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12312}, author = {M.L. Avolio and Koerner, S.E. and Kimberly J. La Pierre and K.R. Wilcox and G.T. Wilson and M.D. Smith and Scott. L. Collins} } @article {KNZ001633, title = {Differential effects of extreme drought on production and respiration: Synthesis and modeling analysis}, journal = {Biogeosciences}, volume = {11}, year = {2014}, pages = {621 -633}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.5194/bg-11-621-2014}, url = {https://www.biogeosciences.net/11/621/2014/}, author = {Shi, Z. and Thomey, M.L. and Mowll, M. and Litvak, M.E. and N. Brunsell and Scott. L. Collins and Pockman, W.T. and M.D. Smith and Alan K. Knapp and Luo, Y.} } @article {KNZ001632, title = {Eutrophication weakens stabilizing effects of diversity in natural grasslands}, journal = {Nature}, volume = {508}, year = {2014}, pages = {521 -525}, abstract = {

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.

}, keywords = {LTER-KNZ, Biodiversity, Community ecology, Grassland ecology}, doi = {10.1038/nature13014}, url = {https://www.nature.com/articles/nature13014}, author = {Hautier, Y. and Seabloom, E.W. and E.T. Borer and P. Adler and Harpole, W.S. and Hillebrand, H. and Lind, E.M. and MacDougall, A.S. and Stevens, C.J. and J.D. Bakker and Buckley, Y.M. and Chu, C. and Scott. L. Collins and Daleo, P. and Damschen, E.I. and Davies, K.F. and Fay, P.A. and Firn, J. and Gruner, D.S. and Jin, V.L. and Klein, J.A. and Knops, J.M.H. and Kimberly J. La Pierre and Li, W. and McCulley, R.L. and Melbourne, B.A. and Joslin L. Moore and O{\textquoteright}Halloran, L.R. and Prober, S.M. and A. Risch and Sankaran, M. and Schuetz, M. and Hector, A.} } @article {KNZ001586, title = {Interactive effects of grazing, drought, and fire on grassland plant communities in North America and South Africa}, journal = {Ecology}, volume = {95}, year = {2014}, pages = {98 -109}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/13-0526.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-0526.1}, author = {Koerner, S.E. and Scott. L. Collins} } @article {KNZ001588, title = {Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa}, journal = {Oecologia}, volume = {175}, year = {2014}, pages = {293 -303}, abstract = {

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.

}, keywords = {LTER-KNZ, disturbance, fire, Grazing, Plant community richness, Species diversity}, doi = {10.1007/s00442-014-2895-9}, url = {https://link.springer.com/article/10.1007\%2Fs00442-014-2895-9}, author = {Eby, S. and Burkepile, D.E. and Fynn, R.W.S. and Burns, C.E. and Govender, N. and Hagenah, N. and Koerner, S.E. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Scott. L. Collins and Kirkman, K.P. and Alan K. Knapp and M.D. Smith} } @article {KNZ001590, title = {Plant community response to loss of large herbivores differs between North American and South African savanna grasslands}, journal = {Ecology}, volume = {95}, year = {2014}, pages = {808 -816}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/13-1828.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/13-1828.1}, author = {Koerner, S.E. and Burkepile, D.E. and Fynn, R.W.S. and Burns, C.E. and Eby, S. and Govender, N. and Hagenah, N. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Scott. L. Collins and Kirkman, K.P. and Alan K. Knapp and M.D. Smith} } @article {KNZ001532, title = {Rainfall variability has minimal effects on grassland recovery from repeated grazing}, journal = {Journal of Vegetation Science}, volume = {25}, year = {2014}, pages = {36 -44}, abstract = {

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.

}, keywords = {LTER-KNZ, Annual net primary production, Climate change, Clipping, disturbance, diversity, Grass{\textendash}forb interaction, Konza, Precipitation, Stem density}, doi = {10.1111/jvs.12065}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12065}, author = {Koerner, S.E. and Scott. L. Collins and John M. Blair and Alan K. Knapp and M.D. Smith} } @article {KNZ001587, title = {Responses to fire differ between South African and North American grassland communities}, journal = {Journal of Vegetation Science}, volume = {25}, year = {2014}, pages = {793 -804}, abstract = {

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.

}, keywords = {LTER-KNZ, Community ecology, Divergence, Fire frequency, Konza Prairie Biological Station, Mesic grassland, nitrogen, Nutrient addition, Richness, tallgrass prairie, Ukulinga Research Farm}, doi = {10.1111/jvs.12130}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12130}, author = {Kirkman, K. and Scott. L. Collins and M.D. Smith and Alan K. Knapp and Burkepile, D.E. and Burns, C.E. and Fynn, R.W.S. and Hagenah, N. and Koerner, S.E. and Matchett, K.J. and Thompson, D.I. and K.R. Wilcox and Wragg, P.D.} } @article {KNZ001626, title = {You are not always what we think you eat: selective assimilation across multiple whole-stream isotopic tracer studies}, journal = {Ecology}, volume = {95}, year = {2014}, pages = {2757 -2767}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/13-2276.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/13-2276.1}, author = {W. K. Dodds and Scott. L. Collins and Hamilton, S.K. and Tank, J.L. and Johnson, S. and Webster, J.R. and Simon, K.S. and M.R. Whiles and Rantala, H.M. and W.H. McDowell and Peterson, S.D. and Riis, T. and Crenshaw, C.L. and Thomas, S.A. and Kristensen, P.B. and Cheever, B.M. and Flecker, A.S. and Griffiths, N.A. and Crowl, T. and Rosi-Marshall, E.J. and El-Sabaawi, R. and Marti, E.} } @article {KNZ001538, title = {Coordinated distributed experiments: an emerging tool for testing global hypotheses in ecology and environmental science}, journal = {Frontiers in Ecology and the Environment}, volume = {11}, year = {2013}, pages = {147 -155}, abstract = {

There is a growing realization among scientists and policy makers that an increased understanding of today\&$\#$39;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.

}, keywords = {LTER-KNZ}, doi = {10.1890/110279}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/110279}, author = {Fraser, L.H. and Henry, H.A. and Carlyle, C.N. and White, S.R. and Beierkuhnlein, C. and Cahill, J.F. and Casper, B.B. and Cleland, E.E. and Scott. L. Collins and Dukes, J.S. and Alan K. Knapp and Lind, E. and Long, R. and Luo, Y. and P.B. Reich and M.D. Smith and Sternberg, M. and Turkington, R.} } @article {KNZ001540, title = {Sensitivity of grassland plant community composition to spatial vs. temporal variation in precipitation}, journal = {Ecology}, volume = {94}, year = {2013}, pages = {1687 -1696}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/12-1006.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/12-1006.1}, author = {Cleland, E.E. and Scott. L. Collins and Dickson, T.L. and Farrer, E.C. and Gross, K.L. and Gherardi, L.A. and Hallett, L.M. and Hobbs, R.J. and Hsu, J.S. and K.N. Suding and Turnbull, L.} } @article {KNZ001541, title = {Small-scale patch structure in North American and South African grasslands responds differently to grazing and fire}, journal = {Landscape Ecology}, volume = {28}, year = {2013}, pages = {1293 -1306}, abstract = {

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.

}, keywords = {LTER-KNZ, Dominance-diversity, Grass-forb interaction, heterogeneity, Konza Prairie, Kruger National Park, Semi-variance}, doi = {10.1007/s10980-013-9866-0}, url = {https://link.springer.com/article/10.1007\%2Fs10980-013-9866-0}, author = {Koerner, S.E. and Scott. L. Collins} } @article {KNZ001495, title = {Effects of fire, grazing and topographic variation on vegetation structure in tallgrass prairie}, journal = {Journal of Vegetation Science}, volume = {23}, year = {2012}, pages = {563 -575}, abstract = {

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.

}, keywords = {LTER-KNZ, disturbance, fire, grassland, Grazing, Plant community structure, Species diversity}, doi = {10.1111/j.1654-1103.2011.01369.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1654-1103.2011.01369.x}, author = {Scott. L. Collins and Calabrese, L.B.} } @article {KNZ001497, title = {Incorporating clonal growth form clarifies the role of plant height in response to nitrogen addition}, journal = {Oecologia}, volume = {169}, year = {2012}, pages = {1053 -1062}, abstract = {

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.

}, keywords = {LTER-KNZ, Clonal growth, Competition, grassland, Nitrogen addition, productivity}, doi = {10.1007/s00442-012-2264-5}, url = {https://link.springer.com/article/10.1007\%2Fs00442-012-2264-5}, author = {Gough, L. and Gross, K.L. and Cleland, E.E. and Clark, C.M. and Scott. L. Collins and Fargione, J.E. and Pennings, S.C. and K.N. Suding} } @article {KNZ001498, title = {Long-term ecological research in a human-dominated world}, journal = {BioScience}, volume = {62}, year = {2012}, pages = {342 -353}, abstract = {

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\&$\#$39;s most difficult environmental challenges. The network\&$\#$39;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.

}, keywords = {LTER-KNZ, coupled natural{\textendash}human systems, cyberinfrastructure, environmental education, environmental observatories, socioecological systems}, doi = {10.1525/bio.2012.62.4.6}, url = {https://academic.oup.com/bioscience/article/62/4/342/243601}, author = {Robertson, G.P. and Scott. L. Collins and D.R. Foster and Brokaw, N. and Ducklow, H.W. and Gragson, T.L. and Gries, C. and Hamilton, S.K. and McGuire, A.D. and Moore, J.C. and Stanley, E.H. and Waide, R.B. and Williams, M.W.} } @booklet {KNZ001539, title = {Long-term trends in ecological systems: a basis for understanding responses to global change. USDA Agriculture Research Service Publication, Technical Bulletin 1931. Washington, D.C}, year = {2012}, abstract = {

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.

}, keywords = {LTER-KNZ, atmospheric chemistry, Climate change, cross-site comparisons, disturbance, ecological response, ecology, ecosystem, EcoTrends, experimental forests, global change, human demography, human population growth, Long Term Ecological Research (LTER), long-term datasets, Precipitation, rangeland, rangeland research stations, surface water chemistry}, author = {Peters, D.P.C. and Laney, C.M. and Lugo, A.E. and Scott. L. Collins and Driscoll, C.T. and Groffman, P.M. and Grove, J.M. and Alan K. Knapp and Kratz, T.K. and Ohman, M.D. and Waide, R.B. and Yao, J.} } @article {KNZ001496, title = {Past, present, and future roles of long-term experiments in the LTER Network}, journal = {Bioscience}, volume = {62}, year = {2012}, pages = {377 -389}, abstract = {

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\&$\#$39;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.

}, keywords = {LTER-KNZ, Climate change, global change, long-term research, LTER Network, multifactor experiments}, doi = {10.1525/bio.2012.62.4.9}, url = {https://academic.oup.com/bioscience/article/62/4/377/243762}, author = {Alan K. Knapp and M.D. Smith and Hobbie, S.E. and Scott. L. Collins and Fahey, T.J. and Hansen, G.J.A. and Landis, D.A. and Kimberly J. La Pierre and Melillo, J.M. and Seastedt, T.R. and Shaver, G.R. and Webster, J.R.} } @article {KNZ001473, title = {Stability of tallgrass prairie during a 19-year increase in growing season precipitation}, journal = {Functional Ecology}, volume = {26}, year = {2012}, pages = {1450 - 1459}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2435.2012.01995.x}, url = {https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2435.2012.01995.x}, author = {Scott. L. Collins and Koerner, S.E. and Plaut, J.A. and Okie, J.G. and Brese, D. and Calabrese, L.B. and Carvajal, A. and Evanse, R.J. and Nonaka, E.} } @article {KNZ001524, title = {A test of two mechanisms proposed to optimize grassland aboveground primary productivity in response to grazing}, journal = {Journal of Plant Ecology}, volume = {5}, year = {2012}, pages = {357 -365}, abstract = {

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.

}, keywords = {LTER-KNZ, aboveground net primary production, fire, forbs, herbivores, savanna}, doi = {10.1093/jpe/rts020}, url = {https://academic.oup.com/jpe/article/5/4/357/908695}, author = {Alan K. Knapp and D.L. Hoover and John M. Blair and Buis, G. and Burkepile, D.E. and Chamberlain, A.J. and Scott. L. Collins and Fynn, R.W.S. and Kirkman, K.P. and M.D. Smith and Blake, D. and Govender , N. and O{\textquoteright}Neal, P. and Schreck, T. and Zinn, A.} } @article {KNZ001460, title = {Woody encroachment decreases diversity across North American grasslands and savannas}, journal = {Ecology}, volume = {93}, year = {2012}, pages = {697 -703}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/11-1199.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/11-1199.1}, author = {Z. Ratajczak and Jesse B. Nippert and Scott. L. Collins} } @article {KNZ001455, title = {Abundance of introduced species at home predicts abundance away in herbaceous communities}, journal = {Ecology Letters}, volume = {14}, year = {2011}, pages = {274 -281}, keywords = {LTER-KNZ}, doi = {10.1111/j.1461-0248.2010.01584.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2010.01584.x}, author = {Firn, J. and Joslin L. Moore and MacDougall, A.S. and E.T. Borer and Seabloom, E.W. and HilleRisLambers, J. and Harpole, W.S. and Cleland, E.E. and C.S. Brown and Knops, J.M.H. and Prober, S.M. and Pyke, D.A. and Farrell, K.A. and J.D. Bakker and O{\textquoteright}Halloran, L.R. and P. Adler and Scott. L. Collins and D{\textquoteright}Antonio, C.M. and Crawley, M.J. and Wolkovich, E.M. and Kimberly J. La Pierre and Melbourne, B.A. and Hautier, Y. and J.W. Morgan and Leakey, A.D.B. and Kay, A.D. and McCulley, R. and Davies, K.F. and Stevens, C.J. and Chu, C. and Holl, K.D. and Klein, J.A. and Fay, P.A. and Hagenah, N. and Kirkman, K.P. and Buckley, Y.M.} } @article {KNZ001454, title = {An integrated conceptual framework for long-term social-ecological research}, journal = {Frontiers in Ecology and the Environment}, volume = {9}, year = {2011}, pages = {351 -357}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/100068}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/100068}, author = {Scott. L. Collins and Carpenter, S.R. and Swinton, S.M. and Orenstein, D.E. and Childers, D.L. and Gragson, T.L. and Grimm, N.B. and Grove, J.M. and Harlan, S.L. and Kaye, J.P. and Alan K. Knapp and Kofinas, G.P. and Magnuson, J.J. and W.H. McDowell and Melack, J.M. and Ogden, L.A. and Robertson, G.R. and M.D. Smith and Whitmer, A.C.} } @article {KNZ001452, title = {Patterns of trait convergence and divergence among native and exotic species in herbaceous plant communities are not modified by nitrogen enrichment}, journal = {Journal of Ecology}, volume = {99}, year = {2011}, pages = {1327 -1338}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2745.2011.01860.x}, url = {https://www.jstor.org/stable/41333056?seq=1$\#$page_scan_tab_contents}, author = {Cleland, E.E. and Clark, C.M. and Scott. L. Collins and Fargione, J.E. and Gough, L. and Gross, K.L. and Pennings, S.C. and K.N. Suding} } @article {KNZ001448, title = {Productivity is a poor predictor of plant species richness}, journal = {Science}, volume = {333}, year = {2011}, pages = {1750 -1753}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1126/science.1204498}, url = {http://science.sciencemag.org/content/333/6050/1750}, author = {P. Adler and Seabloom, E.W. and E.T. Borer and Hillebrand, H. and Hautier, Y. and Hector, A. and Harpole, W.S. and O{\textquoteright}Halloran, L.R. and Grace, J.B. and Anderson, T.M. and J.D. Bakker and L.A. Biederman and C.S. Brown and Buckley, Y.M. and Calabrese, L.B. and Chu, C.J. and Cleland, E.E. and Scott. L. Collins and Cottingham, K.L. and Crawley, M.J. and Damschen, E.I. and Davies, K.F. and DeCrappeo, N.M. and Fay, P.A. and Firn, J. and Frater, P. and Gasarch, E.I. and Gruner, D.S. and Hagenah, N. and HilleRisLambers, J. and Humphries, H.C. and Jin, V.L. and Kay, A. and Kirkman, K.P. and Klein, J.A. and Knops, J.M.H. and Kimberly J. La Pierre and Lambrinos, J.G. and Li, W. and MacDougall, A.S. and McCulley, R.L. and Melbourne, B.A. and Mitchell, C.E. and Joslin L. Moore} } @article {KNZ001300, title = {Fire and grazing in a mesic tallgrass prairie: impacts on plant species and functional traits}, journal = {Ecology}, volume = {91}, year = {2010}, pages = {1651 -1659}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/09-0431.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/09-0431.1}, author = {Spasojevic, M.J. and Aicher, R.J. and Koch, G.R. and Marquardt, E.S. and Mirotchnick, N. and Troxler, T.G. and Scott. L. Collins} } @article {KNZ001259, title = {Controls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison}, journal = {Ecosystems}, volume = {12}, year = {2009}, pages = {982 -995}, abstract = {

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.

}, keywords = {LTER-KNZ, ANPP, fire, Grasslands, Grazing, nitrogen, Savannas}, doi = {10.1007/s10021-009-9273-1}, url = {https://link.springer.com/article/10.1007\%2Fs10021-009-9273-1}, author = {Buis, G.M. and John M. Blair and Burkepile, D.E. and Burns, C.E. and Chamberlain, A.J. and Chapman, P. and Scott. L. Collins and Fynn, R.W.S. and Govender, N. and Kirkman, K. and M.D. Smith and Alan K. Knapp} } @article {KNZ001252, title = {A framework for assessing ecosystem dynamics in response to chronic resource alterations induced by global change}, journal = {Ecology}, volume = {90}, year = {2009}, pages = {3279 -3289}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/08-1815.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/08-1815.1}, author = {M.D. Smith and Alan K. Knapp and Scott. L. Collins} } @article {KNZ001176, title = {Influence of grazing and fire frequency on small-scale plant community structure and resource variability in native tallgrass prairie}, journal = {Oikos}, volume = {117}, year = {2008}, pages = {859 -866}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.0030-1299.2008.16515.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.0030-1299.2008.16515.x}, author = {Veen, G.F. and John M. Blair and M.D. Smith and Scott. L. Collins} } @article {KNZ001181, title = {Rank clocks and plant community dynamics}, journal = {Ecology}, volume = {89}, year = {2008}, pages = {3534 -3541}, abstract = {Summarizing 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.}, keywords = {LTER-KNZ}, doi = {10.1890/07-1646.1}, author = {Scott. L. Collins and K.N. Suding and Cleland, E.E. and Batty, M. and Pennings, S.C. and Gross, K.L. and Grace, J.S. and Gough, L. and Fargione, J.E. and Clark, C.M.} } @article {KNZ001149, title = {Shrub encroachment in North American grasslands: Shifts in growth form dominance rapidly alters control of ecosystem carbon inputs}, journal = {Global Change Biology}, volume = {14}, year = {2008}, pages = {615 -623}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2486.2007.01512.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2486.2007.01512.x}, author = {Alan K. Knapp and J. M. Briggs and Scott. L. Collins and S.R. Archer and Bret-Harte, M.S. and Ewers, B.E. and Peters, D.P. and Young, D.R. and Shaver, G.R. and Pendall, E. and Cleary, M.B.} } @article {KNZ001180, title = {Species responses to nitrogen fertilization in herbaceous plant communities, and associated species traits}, journal = {Ecology}, volume = {89}, year = {2008}, pages = {1175 -}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1890/07-1104.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/07-1104.1}, author = {Cleland, E.E. and Clark, C.M. and Scott. L. Collins and Fargione, J.E. and Gough, L. and Gross, K.L. and Pennings, S.C. and W.D. Bowman and Robertson, G.P. and Simpson, J. and Tilman, D. and K.N. Suding} } @article {KNZ001094, title = {Environmental and plant community determinants ofspecies loss following nitrogen enrichment}, journal = {Ecology Letters}, volume = {10}, year = {2007}, pages = {596 -607}, abstract = {Global 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.}, keywords = {LTER-KNZ}, doi = {10.1111/j.1461-0248.2007.01053.x}, author = {Clark, C.M. and Cleland, E.E. and Scott. L. Collins and Fargione, J.E. and Gough, L. and Pennings, S.C. and K.N. Suding and Grace, J.B.} } @article {KNZ001136, title = {Microbial responses to nitrogen addition in three contrasting grassland ecosystems}, journal = {Oecologia}, volume = {154}, year = {2007}, pages = {349 -359}, abstract = {

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.

}, keywords = {LTER-KNZ, Extracellular enzyme activity, Soil carbon}, doi = {10.1007/s00442-007-0836-6}, author = {Lydia H. Zeglin and Stursova, M. and Sinsabaugh, R.L. and Scott. L. Collins} } @article {KNZ001092, title = {Stream insect occupancy-frequency patterns and metapopulation structure}, journal = {Oecologia}, volume = {151}, year = {2007}, pages = {313 -321}, abstract = {An 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{\textendash}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.}, keywords = {LTER-KNZ, aquatic insect, Core-satellite, Distribution, Sampling intensity, spatial scale}, doi = {10.1007/s00442-006-0596-8}, author = {Heatherly, T. and M.R. Whiles and D.J. Gibson and Scott. L. Collins and Huryn, A.D. and Jackson, J.K. and Palmer, M.A.} } @article {KNZ001031, title = {Scale-dependent interaction of fire andgrazing on community heterogeneity in tallgrass prairie}, journal = {Ecology}, volume = {87}, year = {2006}, pages = {2058 -2067}, abstract = {Natural 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{\textendash}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.}, keywords = {LTER-KNZ}, doi = {10.1890/0012-9658(2006)87[2058:SIOFAG]2.0.CO;2}, author = {Scott. L. Collins and M.D. Smith} } @article {KNZ00977, title = {Do individual plant speciesshow predictable responses to nitrogen addition across multipleexperiments?}, journal = {Oikos}, volume = {110}, year = {2005}, pages = {547 -555}, abstract = {A 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.}, keywords = {LTER-KNZ}, doi = {10.1111/j.0030-1299.2005.13792.x}, author = {Pennings, S.C. and Clark, C.M. and Cleland, E.E. and Scott. L. Collins and Gough, L. and Gross, K.L. and Milchunas, D.G. and K.N. Suding} } @article {KNZ00967, title = {Functional and abundance based mechanisms explain diversity loss due to nitrogen fertilization}, journal = {Proceedings of the National Academy of Sciences}, volume = {102}, year = {2005}, pages = {4387 -4392}, abstract = {Human 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.}, keywords = {LTER-KNZ}, doi = {10.1073/pnas.0408648102}, author = {K.N. Suding and Scott. L. Collins and Gough, L. and Clark, C.M. and Cleland, E.E. and Gross, K.L. and Milchunas, D.G. and Pennings, S.} } @article {KNZ00978, title = {Soil heterogeneity effects on tallgrass prairie community heterogeneity: anapplication of ecological theory to restoration ecology}, journal = {Restoration Ecology}, volume = {13}, year = {2005}, pages = {413 -424}, abstract = {Spatial 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.}, keywords = {LTER-KNZ, grassland, Panicum virgatum, restoration, soil heterogeneity, switchgrass, tallgrass prairie}, doi = {10.1111/j.1526-100X.2005.00051.x}, author = {S.G. Baer and Scott. L. Collins and John M. Blair and Fiedler, A. and Alan K. Knapp} } @article {KNZ00943, title = {Generality in ecology: testing North American grassland rules in South African savannas}, journal = {Frontiers in Ecology and the Environment}, volume = {9}, year = {2004}, pages = {483 -491}, abstract = {Ecology has emerged as a global science, and there is a pressing need to identify ecological rules {\textendash} 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.}, keywords = {LTER-KNZ}, doi = {10.1890/1540-9295(2004)002[0483:GIETNA]2.0.CO;2}, author = {Alan K. Knapp and M.D. Smith and Scott. L. Collins and Zambatis, N. and Peel, M. and Emery, S.M. and Wojdak, J. and Horner-Devine, M.C. and Biggs, H. and Kruger, J. and Andelman, S.J.} } @article {KNZ00840, title = {Needed: A unified infrastructure to support long-term scientific research on public lands}, journal = {Ecological Applications}, volume = {14}, year = {2004}, pages = {18 -21}, keywords = {LTER-KNZ}, doi = {10.1890/03-5106}, author = {Pringle, C.M. and Scott. L. Collins} } @article {KNZ00889, title = {Plant community responses to resource availability and heterogeneity during restoration}, journal = {Oecologia}, volume = {139}, year = {2004}, pages = {617 -629}, abstract = {Availability 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{\textquoteright} 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.}, keywords = {LTER-KNZ, diversity, grassland, nitrogen, tallgrass prairie}, doi = {10.1007/s00442-004-1541-3}, author = {S.G. Baer and John M. Blair and Scott. L. Collins and Alan K. Knapp} } @article {KNZ00839, title = {Disturbance dynamics and ecological response: the contribution of long-term ecological research}, journal = {BioScience}, volume = {53}, year = {2003}, pages = {46 -56}, abstract = {Long-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.}, keywords = {LTER-KNZ, biotic invasion, fire, heterogeneity, hurricane, scale}, doi = { 10.1641/0006-3568(2003)053[0046:DDAERT]2.0.CO;2}, author = {Turner, M.G. and Scott. L. Collins and Lugo, A.L. and Magnuson, J.J. and Rupp, T.S. and Swanson, F.J.} } @article {KNZ00863, title = {Productivity responses to altered rainfall patterns in a C4-dominated grassland}, journal = {Oecologia}, volume = {137}, year = {2003}, pages = {245 -251}, abstract = {Rainfall 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{\textendash}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.}, keywords = {LTER-KNZ, Climate change, Konza Prairie, Net primary productivity, Precipitation, soil moisture}, doi = {10.1007/s00442-003-1331-3}, author = {P. Fay and Carlisle, J.D. and Alan K. Knapp and John M. Blair and Scott. L. Collins} } @article {KNZ00822, title = {Soil resources regulate productivity and diversity in newly established tallgrass prairie}, journal = {Ecology}, volume = {84}, year = {2003}, pages = {724 -735}, abstract = {In 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.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1890/0012-9658(2003)084[0724:SRRPAD]2.0.CO;2}, author = {S.G. Baer and John M. Blair and Alan K. Knapp and Scott. L. Collins} } @article {KNZ005, title = {Altered rainfall patterns, gas exchange and growth in C3 and C4 grassland species}, journal = {International Journal of Plant Sciences}, volume = {163}, year = {2002}, pages = {549 -557}, keywords = {LTER-KNZ}, author = {Fay, P.A. and Carlisle, J.D. and Danner, B.T. and Lett, M.S. and McCarron, J.K. and Stewart, C. and Alan K. Knapp and John M. Blair and Scott. L. Collins} } @article {KNZ00821, title = {Effect of local and regional processes on plant species richness in tallgrass prairie}, journal = {Oikos}, volume = {99}, year = {2002}, pages = {571 -579}, abstract = {Historically, 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.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1034/j.1600-0706.2002.12112.x}, author = {Scott. L. Collins and Glenn, S.M. and J. M. Briggs} } @article {KNZ00827, title = {Rainfall variability, carbon cycling and plant species diversity in a mesic grassland}, journal = {Science}, volume = {298}, year = {2002}, pages = {2202 -2205}, abstract = {

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.

}, keywords = {LTER-KNZ}, doi = {10.1126/science.1076347}, url = {https://science.sciencemag.org/content/298/5601/2202}, author = {Alan K. Knapp and Fay, P.A. and John M. Blair and Scott. L. Collins and M.D. Smith and Carlisle, J.D. and Harper, C.W. and Danner, B.T. and Lett, M.S. and McCarron, J.K.} } @article {KNZ00864, title = {Carbon and water relations of juvenile Quercus species in tallgrass prairie}, journal = {Journal of Vegetation Science}, volume = {12}, year = {2001}, pages = {807 -816}, abstract = {In 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.}, keywords = {LTER-KNZ, Ecotone, Facilitation, forest expansion, Quercus, tallgrass prairie}, doi = {10.2307/3236868}, author = {Fay, P.A. and Carlisle, J.D. and Danner, B.T. and Lett, M.S. and McCarron, J.K. and Stewart, C. and Alan K. Knapp and John M. Blair and Scott. L. Collins} } @article {KNZ00760, title = {Ecological forecasts: an emerging imperative}, journal = {Science}, volume = {293}, year = {2001}, pages = {657 -660}, abstract = {Planning 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.}, keywords = {LTER-KNZ}, doi = {10.1126/science.293.5530.657}, author = {Clark, J.S. and Carpenter, S.R. and Barber, M. and Scott. L. Collins and Dobson, A. and Foley, J.A. and Lodge, D.M. and Pascual, M. and Pielke, R and Pizer, W. and Pringle, C. and Reid, W.V. and Rose, K.A. and Sala, O. and Schlesinger, W.H. and Wall, D.H. and Wear, D.} } @article {KNZ00791, title = {Feedback loops in ecological hierarchies following urine deposition in tallgrass prairie}, journal = {Ecology}, volume = {82}, year = {2001}, pages = {1319 -1329}, abstract = {Although 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.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1890/0012-9658(2001)082[1319:FLIEHF]2.0.CO;2}, author = {Steinauer, M. and Scott. L. Collins} } @proceedings {KNZ007, title = {Interactions between fire and invasive plants in temperate grasslands of North America}, year = {2001}, pages = {40 -65}, publisher = {Tall Timbers Research Station}, address = {Tallahassee, FL}, abstract = {A 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 diversity}, keywords = {LTER-KNZ, alien plants, exotic species, fire, Grasslands, invasive plants, prairie}, author = {Grace, J.B. and M.D. Smith and Grace, S.L. and Scott. L. Collins and Stohlgren, T.J.}, editor = {Galley, K. and Wilson, T.} } @article {KNZ00761, title = {Long-term research and the dynamics of bird populations and communities: an overview}, journal = {Auk}, volume = {118}, year = {2001}, pages = {583 -588}, keywords = {LTER-KNZ}, doi = {10.1642/0004-8038(2001)118[0583:LTRATD]2.0.CO;2}, author = {Scott. L. Collins} } @article {KNZ00762, title = {A method to determine rate and pattern of variability in ecological communities}, journal = {Oikos}, volume = {91}, year = {2001}, pages = {285 -293}, abstract = {It 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{\textendash}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.}, keywords = {LTER-KNZ}, doi = {10.1034/j.1600-0706.2000.910209.x}, author = {Scott. L. Collins and Michelli, F. and Hartt, L.} } @article {KNZ00858, title = {Altering rainfall timing and quantity in a mesic grassland ecosystem: Design and performance of rainfall manipulation shelters}, journal = {Ecosystems}, volume = {3}, year = {2000}, pages = {308 -319}, abstract = {Global 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{\textendash}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{\textendash}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.}, keywords = {LTER-KNZ, Climate change, floristic diversity, Grasslands, Konza Prairie, life histories, long-term research, Net primary production, precipitation patterns, rainout shelters, soil moisture}, doi = {10.1007/s100210000028}, author = {Fay, P.A. and Carlisle, J.D. and Alan K. Knapp and John M. Blair and Scott. L. Collins} } @article {KNZ00727, title = {Disturbance frequency and community stability in native tallgrass prairie}, journal = {The American Naturalist}, volume = {155}, year = {2000}, pages = {311 -325}, abstract = {Ecological 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{\textendash}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.}, keywords = {LTER-KNZ, Community dynamics, community stability, disturbance, fire, tallgrass prairie, temporal variability}, doi = {10.1086/303326}, author = {Scott. L. Collins} } @article {KNZ00720, title = {Ecosystems as functional units in nature}, journal = {Natural Resources and Environment}, volume = {14}, year = {2000}, pages = {150 -155}, keywords = {LTER-KNZ}, author = {John M. Blair and Scott. L. Collins and Alan K. Knapp} } @article {KNZ00734, title = {Fertilization effects of species density and primary productivity in herbaceous plant communities}, journal = {Oikos}, volume = {89}, year = {2000}, pages = {428 -439}, abstract = {Fertilization 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.}, keywords = {LTER-KNZ}, doi = {10.1034/j.1600-0706.2000.890302.x}, author = {Gough, L. and Osenberg, C.W. and Gross, K.L. and Scott. L. Collins} } @article {KNZ00689, title = {The core-satellite species hypothesis provides a theoretical basis for Grimes classification of dominant subordinate, and transient species}, journal = {Journal of Ecology}, volume = {87}, year = {1999}, pages = {1064 -1067}, keywords = {LTER-KNZ}, doi = {10.1046/j.1365-2745.1999.00424.x}, author = {D.J. Gibson and Ely, J.S. and Scott. L. Collins} } @article {KNZ00697, title = {The keystone role of bison in North American tallgrass prairie}, journal = {BioScience}, volume = {49}, year = {1999}, pages = {39 -50}, keywords = {LTER-KNZ}, url = {http://www.jstor.org/stable/10.1525/bisi.1999.49.1.39}, author = {Alan K. Knapp and John M. Blair and J. M. Briggs and Scott. L. Collins and D.C. Hartnett and Johnson, L.C. and Towne, E.G.} } @inbook {KNZ00649, title = {Animal populations and communities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {113 -139}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.W. Kaufman and Kaufman, G.A. and Fay, P.A. and Zimmerman, J.L. and Evans, E.W.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00661, title = {Belowground biology and processes}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {244 -264}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {C. W. Rice and Todd, T.C. and John M. Blair and Seastedt, T.R. and Ramundo, R.A. and G.T. Wilson}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00665, title = {Climate change, elevated CO2 and predictive modeling: Past and future climate change scenarios for the tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {283 -300}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland\%20dynamics\%20ch16.pdf}, author = {Seastedt, T.R. and Hayden, B.P. and Owensby, C.E. and Alan K. Knapp}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00633, title = {Disturbance, diversity and species interactions in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {140 -156}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and Steinauer, E.M.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00648, title = {Diversity of terrestrial macrofauna}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {101 -112}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.W. Kaufman and Fay, P.A. and Kaufman, G.A. and Zimmerman, J.L.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00632, title = {The dynamic tallgrass prairie: Synthesis and research opportunities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {301 -315}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and Alan K. Knapp and D.C. Hartnett and J. M. Briggs}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00639, title = {The flora of Konza Prairie: A historical review and contemporary patterns}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {69 -80}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Freeman, C.C.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00657, title = {Geomorphology of the Konza Prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {35 -47}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Oviatt, C.G.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @book {KNZ001010, title = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {364 -364}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00652, title = {Grasslands, Konza Prairie and long-term ecological Research}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {3 -15}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and Seastedt, T.R.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00642, title = {Hydrology and aquatic chemistry}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {159 -176}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Gray, L.J. and G. L. Macpherson and Koelliker, J.K. and W. K. Dodds}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00626, title = {A landscape perspective of patterns and processes in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {265 -279}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {J. M. Briggs and Nellis, M.D. and Turner, C.L. and Henebry, G.M. and Su, H.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @article {KNZ00631, title = {Modulation of diversity by grazing and mowing in native tallgrass prairie}, journal = {Science}, volume = {280}, year = {1998}, pages = {745 -747}, abstract = {Species 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.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1126/science.280.5364.745}, author = {Scott. L. Collins and Alan K. Knapp and J. M. Briggs and John M. Blair and Steinauer, E.M.} } @inbook {KNZ00651, title = {Patterns and controls of aboveground net primary production in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {193 -221}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and J. M. Briggs and John M. Blair and Turner, C.L.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00645, title = {Plant populations: Patterns and processes}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {81 -100}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.C. Hartnett and Fay, P.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00646, title = {Regional climate and the distribution of tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {19 -34}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland\%20dynamics\%20ch2.pdf}, author = {Hayden, B.P.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00660, title = {Soils and soil biota}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {48 -66}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Ransom, M.D. and C. W. Rice and Todd, T.C. and Wehmueller, W.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00643, title = {Structure and dynamics of aquatic communities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {177 -189}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Gray, L.J. and W. K. Dodds}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00620, title = {Terrestrial nutrient cycling in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-term Ecological Research}, year = {1998}, pages = {222 -243}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {John M. Blair and Seastedt, T.R. and C. W. Rice and Ramundo, R.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @article {KNZ00582, title = {Effects of organismal and distance scaling on analysis of species distribution and abundance}, journal = {Ecological Applications}, volume = {7}, year = {1997}, pages = {543 -551}, abstract = {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 asses organismal effects, we held spatial scale constant and we compared patterns of distribution and abundance among these taxonomic groups. Using long{\textemdash}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 {\textquotedblleft}region{\textquotedblright} 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.}, keywords = {LTER-KNZ}, doi = {10.1890/1051-0761(1997)007[0543:EOOADS]2.0.CO;2}, author = {Scott. L. Collins and Glenn, S.M.} } @article {KNZ00593, title = {Gradient models, gradient analysis and hierarchical structure in plant communities}, journal = {Oikos}, volume = {78}, year = {1997}, pages = {23 -30}, abstract = {Two 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.}, keywords = {LTER-KNZ}, doi = {10.2307/3545796}, author = {Hoagland, B.W. and Scott. L. Collins} } @article {KNZ00583, title = {Intermediate disturbance and its relationship to within-and between-patch structure}, journal = {New Zealand Journal of Ecology}, volume = {21}, year = {1997}, pages = {103 -110}, abstract = {The 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.}, keywords = {LTER-KNZ}, url = {http://www.jstor.org/stable/24054530}, author = {Scott. L. Collins and Glenn, S.M.} } @inbook {KNZ00614, title = {Landscape gradients and habitat structure in native grasslands of the central great plains}, booktitle = {Ecology and Conservation of Great Plains Vertebrates}, year = {1997}, pages = {3 -19}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {New York}, abstract = {Habitat 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 {\textquotedblleft}keystone engineers,{\textquotedblright} 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.}, keywords = {LTER-KNZ}, doi = {10.1007/978-1-4757-2703-6_1}, author = {Vinton, M.A. and Scott. L. Collins}, editor = {Knopf, F.L. and Samson, F.B.} } @inbook {KNZ00569, title = {Prairie ecology-the tallgrass prairie}, booktitle = {Prairie Conservation-Preserving North America{\textquoteright}s Most Endangered Ecosystem}, year = {1996}, pages = {39 -52}, publisher = {Island Press}, organization = {Island Press}, address = {Washington, DC}, keywords = {LTER-KNZ, tallgrass prairie}, url = {https://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\%20Steinauer}, author = {Steinauer, E.M. and Scott. L. Collins}, editor = {Knopf, F.L. and Samson, F.B.} } @inbook {KNZ00529, title = {Spatial and temporal patterns in functional diversity}, booktitle = {Biodiversity: A Biology Of Numbers and Difference}, year = {1996}, pages = {253 -280}, publisher = {Blackwell Science London}, organization = {Blackwell Science London}, keywords = {LTER-KNZ}, author = {Scott. L. Collins and Benning, T.L.}, editor = {Gaston, K.} } @article {KNZ00560, title = {Trophic interactions and plant species richness along a productivity gradient}, journal = {Oikos}, volume = {76}, year = {1996}, pages = {603 -607}, abstract = {We 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.}, keywords = {LTER-KNZ}, doi = {10.2307/3546357}, author = {Moen, J. and Scott. L. Collins} } @article {KNZ00518, title = {Effects of urine deposition on small\-scale patch structure in prairie vegetation}, journal = {Ecology}, volume = {76}, year = {1995}, pages = {1195 -1205}, abstract = {Large 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.}, keywords = {LTER-KNZ}, doi = {10.2307/1940926}, author = {Steinauer, E.M. and Scott. L. Collins} } @article {KNZ00482, title = {Experimental analysis of intermediate disturbance and initial floristic composition: decoupling cause and effect}, journal = {Ecology}, volume = {76}, year = {1995}, pages = {486 -492}, abstract = {The 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{\textemdash}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{\textemdash}causing event in these grasslands, where recovery following disturbance is a balance between immigration and extinction.}, keywords = {LTER-KNZ}, doi = {10.2307/1941207}, author = {Scott. L. Collins and Glenn, S.M. and D.J. Gibson} } @article {KNZ00473, title = {Fine-scale spatial organization of tallgrass prairie vegetation along a topographic gradient}, journal = {Folia Geobot.Phytotax, Praha}, volume = {30}, year = {1995}, pages = {169 -184}, abstract = {Fine-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{\texttimes}5 cm micro-quadrats on each topographic position. Spatial patterns of species and functional groups were analyzed by information theory models ofJuh{\'a}sz-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.}, keywords = {LTER-KNZ, diversity, Functional groups, Grassland community, information theory, Konza Prairie, Scaling, Spatial associations}, doi = {10.1007/BF02812096}, author = {Bartha, S. and Scott. L. Collins and Glenn, S.M. and Kertesz, M.} } @inbook {KNZ00483, title = {Grassland ecosystem and landscape dynamics}, booktitle = {The Changing Prairie}, year = {1995}, pages = {128 -156}, publisher = {Oxford University Press}, organization = {Oxford University Press}, keywords = {LTER-KNZ}, author = {Scott. L. Collins and Glenn, S.M.}, editor = {Anthony Joern and Keeler, K.K.} } @article {KNZ00481, title = {The measurement of stability in grasslands}, journal = {Trends in Ecology and Evolution}, volume = {10}, year = {1995}, pages = {95 -96}, keywords = {LTER-KNZ}, author = {Scott. L. Collins} } @article {KNZ00442, title = {Experimental manipulation of natural plant communities}, journal = {Trends in Ecology and Evolution}, volume = {9}, year = {1994}, pages = {94 -98}, abstract = {Attempts 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.}, keywords = {LTER-KNZ}, doi = {10.1016/0169-5347(94)90203-8}, author = {Gurevitch, J. and Scott. L. Collins} } @proceedings {KNZ00433, title = {Using remote sensing to determine heterogeneity in tallgrass prairie}, year = {1994}, pages = {113 -119}, keywords = {LTER-KNZ, tallgrass prairie}, author = {J. M. Briggs and Scott. L. Collins} } @article {KNZ00401, title = {Experimental analysis of patch dynamics in tallgrass prairie plant communities}, journal = {Journal of Vegetation Science}, volume = {4}, year = {1993}, pages = {157 -162}, abstract = {Previous 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 {\texttimes} 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.}, keywords = {LTER-KNZ, Grassland community, Patch structure, Removal experiment, Schizachyrium scoparium}, doi = {10.2307/3236100}, author = {Glenn, S.M. and Scott. L. Collins} } @article {KNZ00393, title = {The hierarchical continuum concept}, journal = {Journal of Vegetation Science}, volume = {4}, year = {1993}, pages = {149 -156}, abstract = {Two 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{\textquoteright}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{\textendash}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.}, keywords = {LTER-KNZ, community structure, Continuum model, Gradient analysis, Hierarchical structure}, doi = {10.2307/3236099}, author = {Scott. L. Collins and Glenn, S.M. and Roberts, D.W.} } @article {KNZ00386, title = {Mechanisms and processes in vegetation dynamics: Introduction}, journal = {Journal of Vegetation Science}, volume = {4}, year = {1993}, pages = {146 -148}, keywords = {LTER-KNZ}, doi = {10.1111/j.1654-1103.1993.tb01885.x}, author = {Agnew, A.D.Q. and Scott. L. Collins and Maarel, E.} } @article {KNZ00359, title = {Disturbances in tallgrass prairie: local versus regional effects on community heterogeneity}, journal = {Landscape Ecology}, volume = {7}, year = {1992}, pages = {243 -252}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1007/BF00131255}, author = {Glenn, S.M. and Scott. L. Collins and D.J. Gibson} } @article {KNZ00358, title = {Effects of scale and disturbance on rates of immigration and extinction of species in prairies}, journal = {Oikos}, volume = {63}, year = {1992}, pages = {273 -280}, abstract = {

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

}, keywords = {LTER-KNZ, fire}, doi = {http://www.jstor.org/stable/3545388}, author = {Glenn, S.M. and Scott. L. Collins} } @article {KNZ00351, title = {Fire frequency and community heterogeneity in tallgrass prairie vegetation}, journal = {Ecology}, volume = {73}, year = {1992}, pages = {2001 -2006}, abstract = {

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

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2307/1941450}, author = {Scott. L. Collins} } @article {KNZ00312, title = {Importance of spatial and temporal dynamics in species regional abundance and distribution}, journal = {Ecology}, volume = {72}, year = {1991}, pages = {654 -664}, keywords = {LTER-KNZ}, doi = {10.2307/2937205}, author = {Scott. L. Collins and Glenn, S.M.} } @inbook {KNZ00270, title = {Effects of fire on plant community structure in tallgrass prairie}, booktitle = {Fire in North America Tallgrass Prairies}, year = {1990}, pages = {81 -98}, publisher = {University of Oklahoma Press}, organization = {University of Oklahoma Press}, address = {Norman, OK}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and D.J. Gibson}, editor = {Scott. L. Collins and Wallace, L.L.} } @book {KNZ00271, title = {Fire in North American tallgrass prairie}, series = {Fire in North American tallgrass prairie}, year = {1990}, pages = {175 -}, publisher = {University of Oklahoma Press}, organization = {University of Oklahoma Press}, address = {Norman, OK}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and Wallace, L.L.}, editor = {Scott. L. Collins and Wallace, L.L.} } @article {KNZ00268, title = {A hierarchical analysis of species abundance patterns in grassland vegetation}, journal = {The American Midland Naturalist}, volume = {135}, year = {1990}, pages = {633 -648}, keywords = {LTER-KNZ}, doi = {http://www.jstor.org/stable/2462027}, author = {Scott. L. Collins and Glenn, S.M.} } @inbook {KNZ00295, title = {The influence of fire on belowground processes of tallgrass prairies}, booktitle = {Fire in North American Tallgrass Prairie}, year = {1990}, pages = {99 -117}, publisher = {University of Oklahoma Press}, organization = {University of Oklahoma Press}, address = {Norman, OK}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Seastedt, T.R. and Ramundo, R.A.}, editor = {Scott. L. Collins and Wallace, L.L.} } @inbook {KNZ00269, title = {Introduction: Fire as a natural distubance in tallgrass prairie ecosystems}, booktitle = {Fire in North America Tallgrass Prairies}, year = {1990}, pages = {3 -7}, publisher = {University of Oklahoma Press}, organization = {University of Oklahoma Press}, address = {Norman, OK}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins}, editor = {Scott. L. Collins and Wallace, L.L.} } @article {KNZ00279, title = {Patch structure in tallgrass prairies: dynamics of satellite species}, journal = {Oikos}, volume = {57}, year = {1990}, pages = {229 -236}, abstract = {

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

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2307/3565944}, author = {Glenn, S.M. and Scott. L. Collins} } @inbook {KNZ00287, title = {Small mammals and grassland fires}, booktitle = {Fire in North American Tallgrass Prairies}, year = {1990}, pages = {46 -80}, publisher = {University of Okalahoma Press}, organization = {University of Okalahoma Press}, address = {Norman, OK}, abstract = {

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

}, keywords = {LTER-KNZ, fire}, author = {D.W. Kaufman and Finck, E.J. and Kaufman, G.A.}, editor = {Scott. L. Collins and Wallace, L.L.} }