The past few decades have seen an accumulation of evidence that plot-scale species diversity and the abundance of particular species increase ecosystem functioning. Far less is known about other aspects of diversity, such as beta diversity (spatial variation in community composition). Though single functions have typically been the focus of study, ecosystems simultaneously perform many functions. Predicting multifunctionality represents a goal and challenge for ecologists and land managers seeking to obtain a diversity of benefits from ecosystems. Multifunctionality also depends on diversity, in part because different species perform different functions owing to variation in their traits. We hypothesized that beta diversity would increase ecosystem multifunctionality because spatial variation in the species composing the community should give rise to spatial variation in the ecosystem functions performed by the community; over larger spatial scales this should result in greater performance of the suite of functions. This should be true for taxonomic beta diversity (spatial variation in species identity) and should be even more apparent for functional beta diversity (spatial variation in traits of the community). We tested this hypothesis by measuring among-plot beta diversity in plant communities, ten plant traits, and seven ecosystem functions in 29 restored prairies in southwest Michigan.
Results/Conclusions
We found that ecosystem multifunctionality (the average of seven functions) increased with taxonomic beta diversity, but only when we controlled for the abundance of the dominant species (big bluestem, Andropogon gerardii). Functional beta diversity contributed to multifunctionality independently of big bluestem abundance. Prairies with either high big bluestem abundance or high beta diversity had the highest multifunctionality. No prairies had both abundant big bluestem and high beta diversity, likely because big bluestem competitively suppresses the subdominant species that contribute to beta diversity. We found that big bluestem and beta diversity supported multifunctionality differently, by contributing to different individual functions: big bluestem enhanced aboveground productivity and decomposition, taxonomic beta diversity enhanced the cover and diversity of floral resources for pollinators, and functional beta diversity enhanced floral resource diversity and seed removal. When controlling for beta diversity and big bluestem abundance, plot-scale species richness had no effect on multifunctionality, although it did influence individual functions including aboveground productivity, decomposition, and floral resources. These results indicate that beta diversity (functional and taxonomic) and dominant species abundance increase ecosystem multifunctionality, but they do so by contributing to unique ecosystem functions and thus create a variety of types of multifunctionality in different sites.