@article {KNZ002036, title = {Temporal variability in production is not consistently affected by global change drivers across herbaceous-dominated ecosystems}, journal = {Oecologia}, volume = {194}, year = {2020}, pages = {735{\textendash}744}, keywords = {LTER-KNZ}, author = {Avolio, M.L. and Wilcox, K.R. and La Pierre, K.J. and Lemoine, N. and Bowman, W.D. and Collins, S.L. and Knapp, A.K. and Koerner, S.E. and Smith, M.D. and Baer, S.G. and Gross, K.L. and Isbell, F. and McLaren, J. and Reich, P.B. and Suding, K.N. and Suttle, K.B. and Tilman, D. and Xu, Z. and Yu, Q.} } @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 {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 {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 {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 {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.} }