@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 {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 {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 {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 {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 {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 {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 {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 {KNZ00735, title = {Patterns of species density and productivity at different spatial scales in herbaceous plant communities}, journal = {Oikos}, volume = {89}, year = {2000}, pages = {417 -427}, abstract = {A major challenge in evaluating patterns of species richness and productivity involves acquiring data to examine these relationships empirically across a range of ecologically significant spatial scales. In this paper, we use data from herb-dominated plant communities at six Long-Term Ecological Research (LTER) sites to examine how the relationship between plant species density and above-ground net primary productivity (ANPP) differs when the spatial scale of analysis is changed. We quantified this relationship at different spatial scales in which we varied the focus and extent of analysis: (1) among fields within communities, (2) among fields within biomes or biogeographic regions, and (3) among communities within biomes or biogeographic regions. We used species density (D=number of species per m2) as our measure of diversity to have a comparable index across all sites and scales. Although we expected unimodal relationships at all spatial scales, we found that spatial scale influenced the form of the relationship. At the scale of fields within different grassland communities, we detected a significant relationship at only one site (Minnesota old-fields), and it was negative linear. When we expanded the extent of analyses to biogeographic regions (grasslands or North America), we found significant unimodal relationships in both cases. However, when we combined data to examine patterns among community types within different biogeographic regions (grassland, alpine tundra, arctic tundra, or North America), we did not detect significant relationships between species density and ANPP for any region. The results of our analyses demonstrate that the spatial scale of analysis {\textendash} how data are aggregated and patterns examined {\textendash} can influence the form of the relationship between species density and productivity. It also demonstrates the need for data sets from a broad spectrum of sites sampled over a range of scales for examining challenging and controversial ecological hypotheses.}, keywords = {LTER-KNZ}, doi = {10.1034/j.1600-0706.2000.890301.x}, author = {Gross, K.L. and M.R. Whiles and Gough, L. and Inouye, R. and Cox, S.B.} }