@article {KNZ001226,
	title = {Scale-dependent responses of plant biodiversity to nitrogen enrichment},
	journal = {Ecology},
	volume = {89},
	year = {2008},
	pages = {2165 -2171},
	abstract = {Experimental studies demonstrating that nitrogen (N) enrichment reduces plant diversity within individual plots have led to the conclusion that anthropogenic N enrichment is a threat to global biodiversity. These conclusions overlook the influence of spatial scale, however, as N enrichment may alter β diversity (i.e., how similar plots are in their species composition), which would likely alter the degree to which N-induced changes in diversity within localities translate to changes in diversity at larger scales that are relevant to policy and management. Currently, it is unclear how N enrichment affects biodiversity at scales larger than a small plot. We synthesized data from 18 N-enrichment experiments across North America to examine the effects of N enrichment on plant species diversity at three spatial scales: small (within plots), intermediate (among plots), and large (within and among plots). We found that N enrichment reduced plant diversity within plots by an average of 25\% (ranging from a reduction of 61\% to an increase of 5\%) and frequently enhanced β diversity. The extent to which N enrichment altered β diversity, however, varied substantially among sites (from a 22\% increase to an 18\% reduction) and was contingent on site productivity. Specifically, N enrichment enhanced β diversity at low-productivity sites but reduced β diversity at high-productivity sites. N-induced changes in β diversity generally reduced the extent of species loss at larger scales to an average of 22\% (ranging from a reduction of 54\% to an increase of 18\%). Our results demonstrate that N enrichment often reduces biodiversity at both local and regional scales, but that a focus on the effects of N enrichment on biodiversity at small spatial scales may often overestimate (and sometimes underestimate) declines in regional biodiversity by failing to recognize the effects of N on β diversity.},
	keywords = {LTER-KNZ},
	doi = {10.1890/07-0971.1},
	author = {Chalcraft, D.R. and Cox, S.B. and Clark, C.M. and E.E Cleland and K.N. Suding and Weiher, E. and Pennington, D.}
}
@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.}
}
