TY - JOUR T1 - Accounting for herbaceous communities in process‐based models will advance our understanding of “grassy” ecosystems JF - Global Change Biology Y1 - 2023 A1 - K.R. Wilcox A1 - Chen, Anping A1 - M.L. Avolio A1 - Butler, Ethan E. A1 - S.L Collins A1 - Fisher, Rosie A1 - Keenan, Trevor A1 - Kiang, Nancy Y. A1 - Alan K. Knapp A1 - Koerner, S.E. A1 - Kueppers, Lara A1 - Liang, Guopeng A1 - Lieungh, Eva A1 - Loik, Michael A1 - Luo, Yiqi A1 - Poulter, Ben A1 - Reich, Peter A1 - Renwick, Katherine A1 - M. D. Smith A1 - Walker, Anthony A1 - Weng, Ensheng A1 - Komatsu, K.J. VL - 29 UR - https://onlinelibrary.wiley.com/doi/10.1111/gcb.16950 IS - 23 ER - TY - JOUR T1 - Assessing carbon storage capacity and saturation across six central US grasslands using data–model integration JF - Biogeosciences Y1 - 2023 A1 - K.R. Wilcox A1 - S.L Collins A1 - Alan K. Knapp A1 - Pockman, William A1 - Shi, Zheng A1 - M. D. Smith A1 - Luo, Yiqi VL - 20 UR - https://bg.copernicus.org/articles/20/2707/2023/ IS - 13 ER - TY - JOUR T1 - Do trade‐offs govern plant species’ responses to different global change treatments? JF - Ecology Y1 - 2022 A1 - Langley, J. Adam A1 - Grman, Emily A1 - K.R. Wilcox A1 - M.L. Avolio A1 - Kimberly J. Komatsu A1 - Collins, Scott L. A1 - Koerner, S.E. A1 - M. D. Smith A1 - Baldwin, Andrew H. A1 - Bowman, William A1 - Chiariello, Nona A1 - Eskelinen, Anu A1 - Harmens, Harry A1 - Hovenden, Mark A1 - Klanderud, Kari A1 - McCulley, Rebecca L. A1 - Onipchenko, Vladimir G. A1 - Robinson, Clare H. A1 - K.N. Suding VL - 103 UR - https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.3626 IS - 6 JO - Ecology ER - TY - JOUR T1 - Making sense of multivariate community responses in global change experiments JF - Ecosphere Y1 - 2022 A1 - M.L. Avolio A1 - Kimberly J. Komatsu A1 - Koerner, S.E. A1 - Grman, Emily A1 - Isbell, Forest A1 - Johnson, David S. A1 - K.R. Wilcox A1 - Alatalo, Juha M. A1 - Baldwin, Andrew H. A1 - Beierkuhnlein, Carl A1 - Britton, Andrea J. A1 - Foster, Bryan L. A1 - Harmens, Harry A1 - Kern, Christel C. A1 - Li, Wei A1 - McLaren, Jennie R. A1 - Reich, Peter B. A1 - Souza, Lara A1 - Yu, Qiang A1 - Zhang, Yunhai VL - 13 UR - https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecs2.4249 IS - 10 ER - TY - JOUR T1 - N and P constrain C in ecosystems under climate change: role of nutrient redistribution, accumulation, and stoichiometry JF - Ecological Applications Y1 - 2022 A1 - Rastetter, E.B. A1 - Kwiakowski, B.L. A1 - Kicklighter, D.W. A1 - Barker Plotkin, A. A1 - Genet, H. A1 - Jesse B. Nippert A1 - O'Keefe, K. A1 - Perakis, S.R. A1 - Porder, S. A1 - Roley, S.S. A1 - Reuss, R.W. A1 - Thompson, J.R. A1 - Wieder, W.R. A1 - K.R. Wilcox A1 - Yanai, R.D. VL - 32 UR - https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/eap.2684 IS - 8 ER - TY - JOUR T1 - Mass ratio effects underlie ecosystem responses to environmental change JF - Journal of Ecology Y1 - 2020 A1 - M.D. Smith A1 - Koerner, S.E. A1 - Alan K. Knapp A1 - M.L. Avolio A1 - Chaves, F.A. A1 - Denton, E.M. A1 - Dietrich, J. A1 - Gibson, D.J. A1 - Gray, J. A1 - Hoffman, A.M. A1 - Hoover, D.L. A1 - Kimberly J. Komatsu A1 - Silletti, A. A1 - K.R. Wilcox A1 - Yu, Q. A1 - John M. Blair AB -

1. Random species loss has been shown experimentally to reduce ecosystem function, sometimes more than other anthropogenic environmental changes. Yet, controversy surrounds the importance of this finding for natural systems where species loss is non‐random.
2. We compiled data from 16 multi‐year experiments located at a single native tallgrass prairie site. These experiments included responses to 11 anthropogenic environmental changes, as well as non‐random biodiversity loss either the removal of uncommon/rare plant species or the most common (dominant) species.
3. As predicted by the mass ratio hypothesis, loss of a dominant species had large impacts on productivity that were comparable to other anthropogenic drivers. In contrast, the loss of uncommon/rare species had small effects on productivity despite having the largest effects on species richness.
4. The anthropogenic drivers that had the largest effects on productivity nitrogen, irrigation, and fire experienced not only loss of species but also significant changes in the abundance and identity of dominant species.
5. Synthesis. These results suggest that mass ratio effects, rather than species loss per se, are an important determinant of ecosystem function with environmental change.

VL - 108 UR - https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2745.13330 IS - 3 ER - TY - JOUR T1 - A comprehensive approach to analyzing community dynamics using rank abundance curves JF - Ecosphere Y1 - 2019 A1 - M.L. Avolio A1 - Carroll, I. A1 - Scott. L. Collins A1 - Houseman, Gregory R. A1 - Hallett, L.M. A1 - Isbell, F.L. A1 - Koerner, S.E. A1 - Kimberly J. Komatsu A1 - M.D. Smith A1 - K.R. Wilcox AB -

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.

VL - 10 UR - https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecs2.2881 IS - 10 ER - TY - JOUR T1 - Global change effects on plant communities are magnified by time and the number of global change factors imposed JF - Proceedings of the National Academy of Sciences Y1 - 2019 A1 - Kimberly J. Komatsu A1 - M.L. Avolio A1 - Lemoine, Nathan P. A1 - Isbell, Forest A1 - Grman, Emily A1 - Houseman, Gregory R. A1 - Koerner, Sally E. A1 - Johnson, D.S. A1 - K.R. Wilcox A1 - Juha M. Alatalo A1 - Anderson, J.P. A1 - Aerts, R. A1 - S.G. Baer A1 - Baldwin, Andrew H. A1 - Bates, J. A1 - Beierkuhnlein, C. A1 - Belote, R.T. A1 - John M. Blair A1 - Bloor, J.M.G. A1 - Bohlen, P.J. A1 - Edward W. Bork A1 - Elizabeth H. Boughton A1 - W.D. Bowman A1 - Britton, Andrea J. A1 - Cahill, James F. A1 - Chaneton, Enrique J. A1 - Chiariello, N.R. A1 - Cheng, Jimin. A1 - Scott. L. Collins A1 - Cornelissen, J.H.C. A1 - G. Du A1 - Eskelinen, Anu A1 - Firn, Jennifer A1 - Foster, B. A1 - Gough, L. A1 - Gross, K. A1 - Hallett, L.M. A1 - Han, X. A1 - Harmens, H. A1 - Hovenden, M.J. A1 - Jagerbrand, A. A1 - Jentsch, A. A1 - Kern, Christel A1 - Klanderud, Kari A1 - Alan K. Knapp A1 - Kreyling, Juergen A1 - Li, W. A1 - Luo, Yiqi A1 - McCulley, R.L. A1 - McLaren, Jennie R. A1 - Megonigal, Patrick A1 - J.W. Morgan A1 - Onipchenko, Vladimir A1 - Pennings, S.C. A1 - Prevéy, J.S. A1 - Price, Jodi N. A1 - P.B. Reich A1 - Robinson, Clare H. A1 - Russell, L.F. A1 - Sala, O.E. A1 - Seabloom, E.W. A1 - M.D. Smith A1 - Soudzilovskaia, Nadejda A. A1 - Souza, Lara A1 - K.N. Suding A1 - Suttle, B.K. A1 - Svejcar, T. A1 - Tilman, David A1 - Tognetti, P. A1 - Turkington, R. A1 - White, S. A1 - Xu, Zhuwen A1 - Yahdjian, L. A1 - Yu, Q. A1 - Zhang, Pengfei A1 - Zhang, Yunhai AB -

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.

VL - 116 UR - https://www.pnas.org/content/early/2019/08/14/1819027116 IS - 36 ER - TY - JOUR T1 - Ambient changes exceed treatment effects on plant species abundance in long-term global change experiments JF - Glob Chang Biol Y1 - 2018 A1 - Langley, A. A1 - Chapman, S.K. A1 - Kimberly J. La Pierre A1 - M.L. Avolio A1 - W.D. Bowman A1 - Johnson, D. A1 - Isbell, F. A1 - K.R. Wilcox A1 - Foster, B. A1 - Hovenden, M. A1 - Alan K. Knapp A1 - Koerner, S.E. A1 - Lortie, C. A1 - Megonigal, J. A1 - Newton, P. A1 - Reich, B. A1 - M.D. Smith A1 - Suttle, B.K. A1 - Tilman, D. KW - elevated CO2 KW - nitrogen KW - Phosphorus KW - plant community KW - Warming KW - water AB -

The responses of species to environmental changes will determine future community composition and ecosystem function. Many syntheses of global change experiments examine the magnitude of treatment effect sizes, but we lack an understanding of how plant responses to treatments compare to ongoing changes in the unmanipulated (ambient or background) system. We used a database of long-term global change studies manipulating CO2 , nutrients, water, and temperature to answer three questions: (a) How do changes in plant species abundance in ambient plots relate to those in treated plots? (b) How does the magnitude of ambient change in species-level abundance over time relate to responsiveness to global change treatments? (c) Does the direction of species-level responses to global change treatments differ from the direction of ambient change? We estimated temporal trends in plant abundance for 791 plant species in ambient and treated plots across 16 long-term global change experiments yielding 2,116 experiment-species-treatment combinations. Surprisingly, for most species (57%) the magnitude of ambient change was greater than the magnitude of treatment effects. However, the direction of ambient change, whether a species was increasing or decreasing in abundance under ambient conditions, had no bearing on the direction of treatment effects. Although ambient communities are inherently dynamic, there is now widespread evidence that anthropogenic drivers are directionally altering plant communities in many ecosystems. Thus, global change treatment effects must be interpreted in the context of plant species trajectories that are likely driven by ongoing environmental changes.

VL - 24 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14442 IS - 12 ER - TY - JOUR T1 - Asymmetric responses of primary productivity to altered precipitation simulated by ecosystem models across three long-term grassland sites JF - Biogeosciences Y1 - 2018 A1 - Wu, Donghai A1 - Ciais, Philippe A1 - Viovy, Nicolas A1 - Alan K. Knapp A1 - K.R. Wilcox A1 - Michael Bahn A1 - M.D. Smith A1 - Vicca, Sara A1 - Fatichi, Simone A1 - Zscheischler, Jakob A1 - He, Yue A1 - Li, Xiangyi A1 - Ito, Akihiko A1 - Arneth, Almut A1 - Harper, Anna A1 - Ukkola, Anna A1 - Paschalis, Athanasios A1 - Poulter, Benjamin A1 - Peng, Changhui A1 - Ricciuto, Daniel A1 - Reinthaler, David A1 - Chen, Guangsheng A1 - Tian, Hanqin A1 - Genet, élène A1 - Mao, Jiafu A1 - Ingrisch, Johannes A1 - Nabel, Julia E. S. M. A1 - Pongratz, Julia A1 - Lena R. Boysen A1 - Kautz, Markus A1 - Schmitt, Michael A1 - Meir, Patrick A1 - Zhu, Qiuan A1 - R. Hasibeder A1 - Sippel, Sebastian A1 - Dangal, Shree R. S. A1 - Sitch, Stephen A1 - Shi, Xiaoying A1 - Wang, Yingping A1 - Luo, Yiqi A1 - Liu, Yongwen A1 - Piao, Shilong AB -

Field measurements of aboveground net primary productivity (ANPP) in temperate grasslands suggest that both positive and negative asymmetric responses to changes in precipitation (P) may occur. Under normal range of precipitation variability, wet years typically result in ANPP gains being larger than ANPP declines in dry years (positive asymmetry), whereas increases in ANPP are lower in magnitude in extreme wet years compared to reductions during extreme drought (negative asymmetry). Whether the current generation of ecosystem models with a coupled carbon–water system in grasslands are capable of simulating these asymmetric ANPP responses is an unresolved question. In this study, we evaluated the simulated responses of temperate grassland primary productivity to scenarios of altered precipitation with 14 ecosystem models at three sites: Shortgrass steppe (SGS), Konza Prairie (KNZ) and Stubai Valley meadow (STU), spanning a rainfall gradient from dry to moist. We found that (1) the spatial slopes derived from modeled primary productivity and precipitation across sites were steeper than the temporal slopes obtained from inter-annual variations, which was consistent with empirical data; (2) the asymmetry of the responses of modeled primary productivity under normal inter-annual precipitation variability differed among models, and the mean of the model ensemble suggested a negative asymmetry across the three sites, which was contrary to empirical evidence based on filed observations; (3) the mean sensitivity of modeled productivity to rainfall suggested greater negative response with reduced precipitation than positive response to an increased precipitation under extreme conditions at the three sites; and (4) gross primary productivity (GPP), net primary productivity (NPP), aboveground NPP (ANPP) and belowground NPP (BNPP) all showed concave-down nonlinear responses to altered precipitation in all the models, but with different curvatures and mean values. Our results indicated that most models overestimate the negative drought effects and/or underestimate the positive effects of increased precipitation on primary productivity under normal climate conditions, highlighting the need for improving eco-hydrological processes in those models in the future.

VL - 15 UR - https://www.biogeosciences.net/15/3421/2018/ IS - 11 ER - TY - JOUR T1 - Assessing community and ecosystem sensitivity to climate change - toward a more comparative approach JF - Journal of Vegetation Science Y1 - 2017 A1 - M.D. Smith A1 - K.R. Wilcox A1 - Power, Sally A. A1 - Tissue, David T. A1 - Alan K. Knapp AB -

Plant communities can vary widely in their sensitivity to changing precipitation regimes, as reported by Byrne et al., Mulhouse et al. and Sternberg et al. in this issue of Journal of Vegetation Science. But to understand why communities differ in their sensitivity, we argue that clearly defined metrics of sensitivity and coordinated research approaches are needed to elucidate mechanisms.

VL - 28 UR - https://onlinelibrary.wiley.com/doi/full/10.1111/jvs.12524 IS - 2 ER - TY - JOUR T1 - Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments JF - Global Change Biology Y1 - 2017 A1 - K.R. Wilcox A1 - Shi, Zheng A1 - Gherardi, Laureano A. A1 - Lemoine, Nathan P. A1 - Koerner, Sally E. A1 - Hoover, David L. A1 - Bork, Edward A1 - Byrne, Kerry M. A1 - Cahill, James A1 - Scott. L. Collins A1 - Evans, Sarah A1 - Gilgen, Anna K. A1 - Holub, Petr A1 - Jiang, Lifen A1 - Alan K. Knapp A1 - LeCain, Daniel A1 - Liang, Junyi A1 - Garcia-Palacios, Pablo A1 - Peñuelas, Josep A1 - Pockman, William T. A1 - M.D. Smith A1 - Sun, Shanghua A1 - White, Shannon R. A1 - Yahdjian, Laura A1 - Zhu, Kai A1 - Luo, Yiqi AB -

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

VL - 23 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.13706 IS - 10 JO - Glob Change Biol ER - TY - JOUR T1 - Asynchrony among local communities stabilises ecosystem function of metacommunities JF - Ecology Letters Y1 - 2017 A1 - K.R. Wilcox A1 - Tredennick, Andrew T. A1 - Koerner, Sally E. A1 - Grman, Emily A1 - Hallett, Lauren M. A1 - M.L. Avolio A1 - Kimberly J. La Pierre A1 - Houseman, Gregory R. A1 - Isbell, Forest A1 - Johnson, David Samuel A1 - Juha M. Alatalo A1 - Baldwin, Andrew H. A1 - Edward W. Bork A1 - Elizabeth H. Boughton A1 - W.D. Bowman A1 - Britton, Andrea J. A1 - Cahill, James F. A1 - Scott. L. Collins A1 - G. Du A1 - Eskelinen, Anu A1 - Gough, Laura A1 - Jentsch, Anke A1 - Kern, Christel A1 - Klanderud, Kari A1 - Alan K. Knapp A1 - Kreyling, Juergen A1 - Luo, Yiqi A1 - McLaren, Jennie R. A1 - Megonigal, Patrick A1 - Onipchenko, Vladimir A1 - Prevéy, Janet A1 - Price, Jodi N. A1 - Robinson, Clare H. A1 - Sala, Osvaldo E. A1 - M.D. Smith A1 - Soudzilovskaia, Nadejda A. A1 - Souza, Lara A1 - Tilman, David A1 - White, Shannon R. A1 - Xu, Zhuwen A1 - Yahdjian, Laura A1 - Yu, Qiang A1 - Zhang, Pengfei A1 - Zhang, Yunhai ED - Gurevitch, Jessica KW - Alpha diversity KW - alpha variability KW - beta diversity KW - Biodiversity KW - CoRRE data base KW - patchiness KW - Plant communities KW - Primary productivity KW - species synchrony AB -

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.

UR - http://onlinelibrary.wiley.com/doi/10.1111/ele.12861/epdf ER - TY - JOUR T1 - Does ecosystem sensitivity to precipitation at the site-level conform to regional-scale predictions? JF - Ecology Y1 - 2016 A1 - K.R. Wilcox A1 - John M. Blair A1 - M.D. Smith A1 - Alan K. Knapp AB -

Central to understanding global C cycle dynamics is the functional relationship between precipitation and net primary production (NPP). At large spatial (regional) scales, the responsiveness of aboveground NPP (ANPP) to inter-annual variation in annual precipitation (AP; ANPPsensitivity) is inversely related to site-level ANPP, coinciding with turnover of plant communities along precipitation gradients. Within ecosystems experiencing chronic alterations in water availability, plant community change will also occur with unknown consequences for ANPPsensitivity. To examine the role plant community shifts may play in determining alterations in site-level ANPPsensitivity, we experimentally increased precipitation by ~35% for two decades in a native Central US grassland. Consistent with regional models, ANPPsensitivity decreased initially as water availability and ANPP increased. However, ANPPsensitivity shifted back to ambient levels when mesic species increased in abundance in the plant community. Similarly, in grassland sites with distinct mesic and xeric plant communities and corresponding 50% differences in ANPP, ANPPsensitivity did not differ over almost three decades. We conclude that responses in ANPPsensitivity to chronic alterations in water availability within an ecosystem may not conform to regional AP-ANPP patterns, despite expected changes in ANPP and plant communities. The result is unanticipated functional resistance to climate change at the site scale.

VL - 97 UR - https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/15-1437.1 ER - TY - JOUR T1 - Nutrient additions cause divergence of tallgrass prairie plant communities resulting in loss of ecosystem stability JF - Journal of Ecology Y1 - 2016 A1 - Koerner, S.E. A1 - M.L. Avolio A1 - Kimberly J. La Pierre A1 - K.R. Wilcox A1 - M.D. Smith A1 - Scott. L. Collins AB -

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.

VL - 104 UR - https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12610 ER - TY - JOUR T1 - Shared drivers but divergent ecological responses: Insights from long-term experiments in mesic savanna grasslands JF - BioScience Y1 - 2016 A1 - M.D. Smith A1 - Alan K. Knapp A1 - Scott. L. Collins A1 - Burkepile, D.E. A1 - Kirkman, K.P. A1 - Koerner, S.E. A1 - Thompson, D.I. A1 - John M. Blair A1 - Burns, C.E. A1 - Eby, S. A1 - Forrestel, E.J. A1 - Fynn, R.W.S. A1 - Govender, N. A1 - Hagenah, N. A1 - Hoover, D.L. A1 - K.R. Wilcox KW - Aboveground net primary productivity KW - fire KW - grassland KW - Grazing KW - plant community AB -

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.

VL - 66 UR - https://academic.oup.com/bioscience/article/66/8/666/2464141 IS - 8 JO - BioScience ER - TY - JOUR T1 - Stability of grassland soil C and N pools despite 25 years of an extreme climatic and disturbance regime JF - Journal of Geophysical Research: Biogeosciences Y1 - 2016 A1 - K.R. Wilcox A1 - John M. Blair A1 - Alan K. Knapp AB -

Global changes are altering many important drivers of ecosystem functioning, with precipitation amount and disturbance frequency being especially important. Carbon (C) and nitrogen (N) pools are key contemporary attributes of ecosystems that can also influence future C uptake via plant growth. Thus, understanding the impacts of altered precipitation amounts (through controls of primary production inputs) and disturbance regimes (through losses of C and N in biomass) is important to project how ecosystem services will respond to future global changes. A major difficulty inherent within this task is that drivers of ecosystem function and processes often interact, resulting in novel ecosystem responses. To examine how changes in precipitation affect grassland ecosystem responses under a frequent disturbance regime (annual fire), we assessed the biogeochemical and ecological consequences of more than two decades of irrigation in an annually burned mesic grassland in the central United States. In this experiment, precipitation amount was increased by 31% relative to ambient and 1 in 3 years were statistically extreme relative to the long-term historical record. Despite evidence that irrigation decreased root:shoot ratios and increased rates of N cycling—each expected to reduce soil C and N with annual burning—we detected no changes in these biogeochemical pools. This surprising biogeochemical resistance highlights the need to explore additional mechanisms within long-term experiments concerning the consequences of global change impacts on ecosystems.

VL - 121 UR - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016JG003370 IS - 7 ER - TY - THES T1 - Assessing grassland sensitivity to global change Y1 - 2015 A1 - K.R. Wilcox PB - Colorado State University CY - Fort Collins, CO VL - PhD. Dissertation UR - https://mountainscholar.org/handle/10217/167147 ER - TY - JOUR T1 - Characterizing differences in precipitation regimes of extreme wet and dry years: Implications for climate change experiments JF - Global Change Biology Y1 - 2015 A1 - Alan K. Knapp A1 - D.L. Hoover A1 - K.R. Wilcox A1 - M.L. Avolio A1 - Koerner, S.E. A1 - Kimberly J. La Pierre A1 - Loik, M.E. A1 - Luo, Y. A1 - Sala, O.E. A1 - M.D. Smith KW - rainfall patterns AB -

Climate change is intensifying the hydrologic cycle and is expected to increase the frequency of extreme wet and dry years. Beyond precipitation amount, extreme wet and dry years may differ in other ways, such as the number of precipitation events, event size, and the time between events. We assessed 1614 long-term (100 year) precipitation records from around the world to identify key attributes of precipitation regimes, besides amount, that distinguish statistically extreme wet from extreme dry years. In general, in regions where mean annual precipitation (MAP) exceeded 1000 mm, precipitation amounts in extreme wet and dry years differed from average years by ~40% and 30%, respectively. The magnitude of these deviations increased to >60% for dry years and to >150% for wet years in arid regions (MAP<500 mm). Extreme wet years were primarily distinguished from average and extreme dry years by the presence of multiple extreme (large) daily precipitation events (events >99th percentile of all events); these occurred twice as often in extreme wet years compared to average years. In contrast, these large precipitation events were rare in extreme dry years. Less important for distinguishing extreme wet from dry years were mean event size and frequency, or the number of dry days between events. However, extreme dry years were distinguished from average years by an increase in the number of dry days between events. These precipitation regime attributes consistently differed between extreme wet and dry years across 12 major terrestrial ecoregions from around the world, from deserts to the tropics. Thus, we recommend that climate change experiments and model simulations incorporate these differences in key precipitation regime attributes, as well as amount into treatments. This will allow experiments to more realistically simulate extreme precipitation years and more accurately assess the ecological consequences.

VL - 21 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.12888 ER - TY - JOUR T1 - Contrasting above- and belowground sensitivity of three Great Plains grasslands to altered rainfall regimes JF - Global Change Biology Y1 - 2015 A1 - K.R. Wilcox A1 - Von Fischer, J.C. A1 - Muscha, J.M. A1 - Petersen, M.K. A1 - Alan K. Knapp AB -

Intensification of the global hydrological cycle with atmospheric warming is expected to increase interannual variation in precipitation amount and the frequency of extreme precipitation events. Although studies in grasslands have shown sensitivity of aboveground net primary productivity (ANPP) to both precipitation amount and event size, we lack equivalent knowledge for responses of belowground net primary productivity (BNPP) and NPP. We conducted a 2-year experiment in three US Great Plains grasslands – the C4-dominated shortgrass prairie (SGP; low ANPP) and tallgrass prairie (TGP; high ANPP), and the C3-dominated northern mixed grass prairie (NMP; intermediate ANPP) – to test three predictions: (i) both ANPP and BNPP responses to increased precipitation amount would vary inversely with mean annual precipitation (MAP) and site productivity; (ii) increased numbers of extreme rainfall events during high-rainfall years would affect high and low MAP sites differently; and (iii) responses belowground would mirror those aboveground. We increased growing season precipitation by as much as 50% by augmenting natural rainfall via (i) many (11–13) small or (ii) fewer (3–5) large watering events, with the latter coinciding with naturally occurring large storms. Both ANPP and BNPP increased with water addition in the two C4 grasslands, with greater ANPP sensitivity in TGP, but greater BNPP and NPP sensitivity in SGP. ANPP and BNPP did not respond to any rainfall manipulations in the C3-dominated NMP. Consistent with previous studies, fewer larger (extreme) rainfall events increased ANPP relative to many small events in SGP, but event size had no effect in TGP. Neither system responded consistently above- and belowground to event size; consequently, total NPP was insensitive to event size. The diversity of responses observed in these three grassland types underscores the challenge of predicting responses relevant to C cycling to forecast changes in precipitation regimes even within relatively homogeneous biomes such as grasslands.

VL - 21 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.12673 ER - TY - JOUR T1 - Stoichiometric homeostasis predicts plant species dominance, temporal stability and responses to global change JF - Ecology Y1 - 2015 A1 - Yu, Q. A1 - K.R. Wilcox A1 - Kimberly J. La Pierre A1 - Alan K. Knapp A1 - Han, X. A1 - M.D. Smith AB -

Why some species are consistently more abundant than others, and predicting how species will respond to global change, are fundamental questions in ecology. Long-term observations indicate that plant species with high stoichiometric homeostasis for nitrogen (HN), i.e., the ability to decouple foliar N levels from variation in soil N availability, were more common and stable through time than low HN species in a central US grassland. However, with 9-yrs of nitrogen addition, species with high HN decreased in abundance, while those with low HN increased in abundance. In contrast, in climate change experiments simulating a range of forecast hydrologic changes - extreme drought (2-yrs), increased rainfall variability (14-yrs), and chronic increases in rainfall (21-yrs) - plant species with the highest HN were least responsive to changes in soil water availability. These results suggest that HN may be predictive of plant species success and stability, and how plant species and ecosystems will respond to global-change driven alterations in resource availability.

VL - 96 UR - https://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/14-1897.1 IS - 9 ER - TY - JOUR T1 - Changes in plant community composition, not diversity, during a decade of nitrogen and phosphorus additions drive above-ground productivity in a tallgrass prairie JF - Journal of Ecology Y1 - 2014 A1 - M.L. Avolio A1 - Koerner, S.E. A1 - Kimberly J. La Pierre A1 - K.R. Wilcox A1 - G.T. Wilson A1 - M.D. Smith A1 - Scott. L. Collins AB -

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.

VL - 102 UR - https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2745.12312 ER - TY - JOUR T1 - Loss of a large grazer impacts savanna grassland plant communities similarly in North America and South Africa JF - Oecologia Y1 - 2014 A1 - Eby, S. A1 - Burkepile, D.E. A1 - Fynn, R.W.S. A1 - Burns, C.E. A1 - Govender, N. A1 - Hagenah, N. A1 - Koerner, S.E. A1 - Matchett, K.J. A1 - Thompson, D.I. A1 - K.R. Wilcox A1 - Scott. L. Collins A1 - Kirkman, K.P. A1 - Alan K. Knapp A1 - M.D. Smith KW - disturbance KW - fire KW - Grazing KW - Plant community richness KW - Species diversity AB -

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.

VL - 175 UR - https://link.springer.com/article/10.1007%2Fs00442-014-2895-9 ER - TY - JOUR T1 - Plant community response to loss of large herbivores differs between North American and South African savanna grasslands JF - Ecology Y1 - 2014 A1 - Koerner, S.E. A1 - Burkepile, D.E. A1 - Fynn, R.W.S. A1 - Burns, C.E. A1 - Eby, S. A1 - Govender, N. A1 - Hagenah, N. A1 - Matchett, K.J. A1 - Thompson, D.I. A1 - K.R. Wilcox A1 - Scott. L. Collins A1 - Kirkman, K.P. A1 - Alan K. Knapp A1 - M.D. Smith AB -

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.

VL - 95 UR - https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/13-1828.1 ER - TY - JOUR T1 - Responses to fire differ between South African and North American grassland communities JF - Journal of Vegetation Science Y1 - 2014 A1 - Kirkman, K. A1 - Scott. L. Collins A1 - M.D. Smith A1 - Alan K. Knapp A1 - Burkepile, D.E. A1 - Burns, C.E. A1 - Fynn, R.W.S. A1 - Hagenah, N. A1 - Koerner, S.E. A1 - Matchett, K.J. A1 - Thompson, D.I. A1 - K.R. Wilcox A1 - Wragg, P.D. KW - Community ecology KW - Divergence KW - Fire frequency KW - Konza Prairie Biological Station KW - Mesic grassland KW - nitrogen KW - Nutrient addition KW - Richness KW - tallgrass prairie KW - Ukulinga Research Farm AB -

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.

VL - 25 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12130 ER -