02031nas a2200229 4500008004100000245011400041210006900155260002400224300001300248520129100261100002001552700001901572700001901591700001501610700001801625700001501643700002001658700001901678700001601697700002001713856006801733 2008 eng d00aEcological consequences of the replacement of native grassland by Juniperus virginiana and other woody plants0 aEcological consequences of the replacement of native grassland b bSpringer-Verlag, NY a156 -1693 a

Although grasslands have been altered by humans for thousands of years (Wedel 1961; Bond et al. 2003), the loss of grassland as a result of anthropogenic activities has increased dramatically over the past 150 years. When Europeans first settled the Midwest and Great Plains, the greatest threat to native grasslands was the conversion of the most highly productive of these ecosystems to row-crop agriculture (Samson and Knopf 1994). Later, with improvements in soil moisture management and irrigation technology, even low-productivity grasslands were plowed. Today, those remnants of the most productive grasslands that escaped the plow are threatened, as are most of Earth’s ecosystems, by a variety of global change phenomena (Vitousek et al. 1997), with the invasion and expansion of woody species into grasslands one of the greatest of these threats. The replacement of grasslands by shrubland, woodland, and forest is a concern not only in the United States but worldwide (Archer et al. 1988; Van Auken 2000; Roques et al. 2001; Silva et al. 2001). Species of woody plants that invade grasslands may include both native plants which previously existed as more minor components of the ecosystem as well as alien species (Bragg and Hulbert 1976; Harcombe et al. 1993).

1 aKnapp, Alan, K.1 aMcCarron, J.K.1 aSilletti, A.M.1 aHoch, G.A.1 aHeisler, J.L.1 aLett, M.S.1 aBlair, John, M.1 aBriggs, J., M.1 aSmith, M.D.1 aVan Auken, O.W. uhttps://link.springer.com/chapter/10.1007%2F978-0-387-34003-6_801955nas a2200253 4500008004100000245010600041210006900147300001300216490000700229520114300236653000901379653001501388653001201403653002201415653002101437100001901458700002001477700002001497700001801517700001501535700001501550700001901565856011701584 2005 eng d00aAn ecosystem in transition: causes and consequences of the conversion of mesic grassland to shrubland0 aecosystem in transition causes and consequences of the conversio a243 -2540 v553 aWoody plant expansion is one of the greatest contemporary threats to mesic grasslands of the central United States. In this article, we synthesize more than 20 years of research to elucidate the causes and consequences of the ongoing transition of C4-dominated grasslands to savanna-like ecosystems codominated by grasses and woody plants. This transition is contingent on fire-free intervals, which provide the opportunity for recruitment both of new individuals and of additional shrub and tree species into this grassland. Once shrubs establish, their cover increases regardless of fire frequency, and infrequent fires accelerate the spread of some shrub species. This process has resulted in a new dynamic state of shrub–grass coexistence in the mesic grasslands of North America. Important consequences of this shift in plant life-form abundance include alterations in plant productivity, species diversity, and carbon storage. Without drastic measures such as mechanical removal of shrubs, it is unlikely that management of fire and grazing regimes alone will be sufficient to restore historic grass dominance in these ecosystems.10afire10aGrasslands10aGrazing10atallgrass prairie10awoody vegetation1 aBriggs, J., M.1 aKnapp, Alan, K.1 aBlair, John, M.1 aHeisler, J.L.1 aHoch, G.A.1 aLett, M.S.1 aMcCarron, J.K. uhttp://knz.lternet.edu/content/ecosystem-transition-causes-and-consequences-conversion-mesic-grassland-shrubland03013nas a2200181 4500008004100000245010300041210006900144300001000213490000700223520236700230100001802597700001602615700001602631700002002647700002002667700001902687856012502706 2004 eng d00aBarley yellow dwarf disease in natural populations of dominant tallgrass prairie species in Kansas0 aBarley yellow dwarf disease in natural populations of dominant t a574 -0 v883 aThe grasses Sorghastrum nutans (Indian grass), Schizachyrium scoparium (little bluestem), Panicum virgatum (switchgrass), and Andropogon gerardii (big bluestem) are four of the most common plant species present in a tallgrass prairie (1). Infection with barley yellow dwarf virus (BYDV, family Luteoviridae) is of interest in these species because of the potential effects of the virus on tallgrass prairie plant communities and the potential for tallgrass prairie to function as a reservoir of the virus for infection in wheat or barley fields. In a previous inoculation experiment, an unidentified strain of BYDV transmitted by the aphid species Rhopalosiphum padi was reported to infect S. scoparium but none of the other three grass species (2). We sampled for the presence of five virus strains in at least 50 blooming plants of each grass species in a natural tallgrass prairie stand in August 2000. Samples were collected in watersheds that were designated 1B, 1D, K1A, 20B, and 20C at Konza Prairie Biological Station in the Flint Hills near Manhattan, KS. To detect the virus, we used enzyme-linked immunosorbent assay (ELISA) with antibodies purchased from Agdia (Elkhart, IN). For the PAV, MAV, RMV, and SGV strains, we used double-antibody sandwich ELISA with alkaline phosphatase label. For Cereal yellow dwarf virus (RPV), we used compound direct ELISA with alkaline phosphatase label. The scoring of ELISA results was based on comparison with infected and uninfected control plants of the same species. Symptoms of infection in the field were difficult to interpret visually, since plants in this natural environment often showed multiple symptoms of stress. None of the five strains were detected in 51 individuals of S. nutans. For 50 individuals of S. scoparium, the incidence of infection by the different strains was 4% for MAV, 0% for PAV, 2% for RMV, 0% for RPV, and 58% for SGV. For 51 individuals of P. virgatum, the incidence of infection was 31% for MAV, 0% for PAV, 0% for RMV, 0% for RPV, and 4% for SGV. For 64 individuals of A. gerardii, the incidence of infection was 59% for MAV, 0% for PAV, 0% for RMV, 0% for RPV, and 3% for SGV. The impact of BYDV on these tallgrass prairie species remains to be determined. The PAV strain is the most commonly reported strain in wheat in Kansas but was not recovered from these grass species.1 aGarrett, K.A.1 aDendy, S.P.1 aPower, A.G.1 aBlaisdell, G.K.1 aAlexander, H.M.1 aMcCarron, J.K. uhttp://knz.lternet.edu/content/barley-yellow-dwarf-disease-natural-populations-dominant-tallgrass-prairie-species-kansas02741nas a2200229 4500008004100000245010100041210006900142300001500211490000700226520198700233653000702220653000702227653002202234653000902256653001002265653002202275653003202297653002002329100001902349700002002368856012302388 2003 eng d00aC3 shrub expansion in a C4 grassland: positive post-fire responses in resources and shoot growth0 aC3 shrub expansion in a C4 grassland positive postfire responses a1496 -15010 v903 aChanges in land management and reductions in fire frequency have enabled woody species to increase in grasslands worldwide. Nevertheless, fire is rarely eliminated from grasslands, and for shrubs to survive, they must be able cope with fire and replace aboveground structures. Because new shoots may have more available solar radiation, greater root : shoot ratios, and thus more resources available belowground after fire compared to undisturbed shrub communities, we hypothesized that carbon, nutrient, and water relations may be enhanced in stems compared to those in an undisturbed grassland. However, this same post-fire resource pulse stimulates the grasses and may intensify competitive interactions between shrubs and grasses. To test these predictions, we measured seasonal patterns in net photosynthesis (A), predawn xylem pressure potentials (XPP), leaf nitrogen (N) content, and productivity of Cornus drummondii shoots from shrub patches (islands) of different sizes in mesic grasslands burned annually, burned infrequently, and protected from fire. Seasonal average A was 20% higher (P = 0.016) in burned than in unburned shrubs, regardless of island size. Shrubs in burned sites also produced shoots with higher leaf N than unburned shrubs, and N content was higher in leaves from small islands compared to large islands (P < 0.0001). Burning caused a decrease in late summer predawn XPP in small islands (−3.1 MPa), whereas burned large islands did not differ from unburned shrubs. Post-fire productivity of new shoots was significantly greater compared to shoots in unburned sites. These results indicate that a transient period of high resource availability after fire allows for increased growth and rapid recovery of grassland shrubs. Thus, although fire has a negative effect on aboveground biomass of shrubs, the post-fire increases in resource availability, which enhance growth in the dominant grasses, are also important for recovery of woody species.10aC310aC410aCornus drummondii10afire10ashrub10atallgrass prairie10atransient maxima hypothesis10awoody expansion1 aMcCarron, J.K.1 aKnapp, Alan, K. uhttp://knz.lternet.edu/content/c3-shrub-expansion-c4-grassland-positive-post-fire-responses-resources-and-shoot-growth00772nas a2200205 4500008004100000245010400041210006900145260004400214300001300258653002200271100001200293700002000305700002000325700001900345700001700364700001900381700001800400700002000418856012800438 2003 eng d00aRainfall timing, soil moisture dynamics, and plant responses in a mesic tallgrass prairie ecosystem0 aRainfall timing soil moisture dynamics and plant responses in a  aTucson, AZbUniversity of Arizona Press a147 -16310atallgrass prairie1 aFay, P.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCarlisle, J.D.1 aDanner, B.T.1 aMcCarron, J.K.1 aWeltzin, J.F.1 aMcPherson, G.R. uhttp://knz.lternet.edu/content/rainfall-timing-soil-moisture-dynamics-and-plant-responses-mesic-tallgrass-prairie-ecosystem02062nas a2200205 4500008004100000245007300041210006900114300001300183490000800196520140000204653001901604653002101623653001901644653001801663653002001681100001901701700002001720700002001740856009601760 2003 eng d00aSoil C and N responses to woody plant expansion in a mesic grassland0 aSoil C and N responses to woody plant expansion in a mesic grass a183 -1920 v2573 aChanges in land management and reductions in fire frequency have contributed to increased cover of woody species in grasslands worldwide. These shifts in plant community composition have the potential to alter ecosystem function, particularly through changes in soil processes and properties. In semi-arid grasslands, the invasion of shrubs and trees is often accompanied by increases in soil resources and more rapid N and C cycling. We assessed the effects of shrub encroachment in a mesic grassland in Kansas (USA) on soil CO2 flux, extractable inorganic N, and N mineralization beneath shrub communities (Cornus drummondii) and surrounding undisturbed grassland sites. In this study, a shift in plant community composition from grassland to shrubland resulted in a 16% decrease in annual soil CO2 flux(4.78 kg CO2 m−2 year−1 for shrub dominated sites versus 5.84 kg CO2 m−2 year−1 for grassland sites) with no differences in total soil C or N or inorganic N. There was considerable variability in N mineralization rates within sites, which resulted in no overall difference in cumulative N mineralized during this study (4.09 g N m−2 for grassland sites and 3.03 g N m−2 for shrub islands). These results indicate that shrub encroachment into mesic grasslands does not significantly alter N availability (at least initially), but does alter C cycling by decreasing soil CO2 flux.10aN availability10aN mineralization10ashrub invasion10asoil CO2 flux10asoil properties1 aMcCarron, J.K.1 aKnapp, Alan, K.1 aBlair, John, M. uhttp://knz.lternet.edu/content/soil-c-and-n-responses-woody-plant-expansion-mesic-grassland00700nas a2200205 4500008004100000245008600041210006900127300001300196490000800209100001400217700001900231700001700250700001500267700001900282700001600301700002000317700002000337700002400357856011300381 2002 eng d00aAltered rainfall patterns, gas exchange and growth in C3 and C4 grassland species0 aAltered rainfall patterns gas exchange and growth in C3 and C4 g a549 -5570 v1631 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/altered-rainfall-patterns-gas-exchange-and-growth-c3-and-c4-grassland-species00542nas a2200133 4500008004100000245007800041210006900119260004300188300001100231490002100242653002200263100001900285856010400304 2002 eng d00aEcological interactions between grasses and shrubs in a tallgrass prairie0 aEcological interactions between grasses and shrubs in a tallgras aManhattan, KSbKansas State University a1 -1110 vPhD Dissertation10atallgrass prairie1 aMcCarron, J.K. uhttp://knz.lternet.edu/content/ecological-interactions-between-grasses-and-shrubs-tallgrass-prairie01540nas a2200229 4500008004100000245009000041210006900131300001500200490000800215520084900223100002001072700001401092700002001106700002401126700001601150700001901166700001701185700001701202700001501219700001901234856005701253 2002 eng d00aRainfall variability, carbon cycling and plant species diversity in a mesic grassland0 aRainfall variability carbon cycling and plant species diversity  a2202 -22050 v2983 a

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

1 aKnapp, Alan, K.1 aFay, P.A.1 aBlair, John, M.1 aCollins, Scott., L.1 aSmith, M.D.1 aCarlisle, J.D.1 aHarper, C.W.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K. uhttps://science.sciencemag.org/content/298/5601/220201943nas a2200133 4500008004100000245009400041210006900135300001500204490000700219520148600226100001901712700002001731856005801751 2001 eng d00aC3 woody plant expansion in a C4 grassland: are grasses and shrubs functionally distinct?0 aC3 woody plant expansion in a C4 grassland are grasses and shrub a1818 -18230 v883 a

The expansion of C3 shrubs into C4-dominated tallgrass prairies represents a fundamental shift in growth-form dominance accompanied by changes in resource acquisition and use. We assessed these changes by comparing the ecophysiological traits of the dominant C4 grass Andropogon gerardii, with traits of three C3 invasive shrub species, Cornus drummondii, Prunus americana, and Rhus glabra. We tested the hypothesis that ecophysiological traits of the shrubs would be similar within this growth form but distinct from grasses and that these species would conform to the two-layer soil water model. Photosynthetic rates in R. glabra were similar to A. gerardii and higher than in the other two shrubs, while water use efficiency was markedly greater in A. gerardii. Among all species, midday xylem pressure potentials (XPP) were distinctly lower (70%) for P. americana, but were similar among the other species. Predawn XPP was related to soil water at shallow depths for A. gerardii (r2 = 0.59) and P. americana (r2 = 0.62), and to deeper soil moisture for R. glabra (r2 = 0.63); there was no relationship for C. drummondii at any soil depth. Thus, a simple two-layer soil water model for partitioning shrub/grass resource acquisition was not appropriate for this grassland. We conclude that these shrubs could not be considered functional equivalents from an ecophysiological perspective, nor were they, as a group, distinct from A. gerardii in resource acquisition and use

1 aMcCarron, J.K.1 aKnapp, Alan, K. uhttp://www.amjbot.org/cgi/content/abstract/88/10/181802614nas a2200277 4500008004100000245008000041210006900121300001300190490000700203520177300210653001201983653001701995653002102012653001202033653002202045100001402067700001902081700001702100700001502117700001902132700001602151700002002167700002002187700002402207856010502231 2001 eng d00aCarbon and water relations of juvenile Quercus species in tallgrass prairie0 aCarbon and water relations of juvenile Quercus species in tallgr a807 -8160 v123 aIn ecosystems where environments are extreme, such as deserts, adult plant species may facilitate the establishment and growth of seedlings and juveniles. Because high temperatures and evaporative demand characterize tall-grass prairies of the central United States (relative to forests), we predicted that the grassland-forest ecotone, by minimizing temperature extremes and moderating water stress, may function to facilitate the expansion of Quercus species into undisturbed tall-grass prairie. We assessed the carbon and water relations of juvenile Quercus macrocarpa and Q. muhlenbergii, the dominant tree species in gallery forests of northeast Kansas, in ecotone and prairie sites. To evaluate the potentially competitive effects of neighboring herbaceous biomass on these oaks, juveniles (< 0.5 m tall) of both species also were subjected to either: (1) removal of surrounding above-ground herbaceous biomass, or (2) control (prairie community intact) treatments. Herbaceous biomass removal had no significant effect on gas exchange or water relations in these oak species in either the prairie or the ecotone environment. Although the ecotone did alleviate some environmental extremes, photosynthetic rates and stomatal conductance were ca. 20 % higher (p < 0.05) in both oaks in prairie sites vs. the ecotone. Moreover, although leaf temperatures on average were higher in oaks in the prairie, high leaf temperatures in the ecotone had a greater negative effect on photosynthesis. These data suggest that the grassland-forest ecotone did not facilitate the growth of Quercus juveniles expanding into this grassland. Moreover, the carbon and water relations of juvenile oaks in the prairie appeared to be unaffected by the presence of the dominant C4 grasses.10aEcotone10aFacilitation10aforest expansion10aQuercus10atallgrass prairie1 aFay, P.A.1 aCarlisle, J.D.1 aDanner, B.T.1 aLett, M.S.1 aMcCarron, J.K.1 aStewart, C.1 aKnapp, Alan, K.1 aBlair, John, M.1 aCollins, Scott., L. uhttp://knz.lternet.edu/content/carbon-and-water-relations-juvenile-quercus-species-tallgrass-prairie