Widespread evidence exists for a positive relationship between biodiversity and ecosystem functioning (BEF), yet this evidence is based largely on measures of taxonomic diversity (richness), simple measures of functioning (biomass), and small-scale experiments that may not fully represent diversity-function relationships in natural systems. Important questions remain about how different measures of biodiversity, including those that incorporate functional trait and phylogenetic information, relate to aspects of ecosystem functioning and multi-functionality. Scaling up BEF relationships must also account for variation in functioning related to environmental conditions rather than diversity. These gaps in understanding limit the application of BEF theory to guiding conservation and restoration. In 29 prairies restored through seed sowing on former agricultural lands, we investigated how taxonomic, phylogenetic, or functional diversity, or environmental conditions, predicted six ecosystem functions and multi-functionality. We calculated taxonomic diversity based on plant community composition, functional diversity based on 10 measured traits, and phylogenetic diversity based on a phylogenetic tree of all species at our sites. We then used model selection to determine which diversity metric and/or set of environmental conditions best predicts individual functions and multi-functionality across our sites.
Among measures of diversity, phylogenetic diversity best predicted multi-functionality, with more phylogenetically diverse sites having greater levels of multi-functionality. Landscape context was also an important predictor of multi-functionality, with sites surrounded by forests and grasslands rather than agriculture and urbanization having higher levels of multi-functionality. Our ability to predict individual functions was variable and three of the six functions had no significant predictors. Functional diversity was positivity related to floral resource availability, with more floral resources being produced on more functionally diverse sites. Soil moisture was positively related to aboveground biomass production, with greater biomass production on wetter sites. Finally, taxonomic diversity was negatively related and site age positively related to decomposition rate, with the highest decomposition rates on older, less diverse sites. Together, these findings suggest that both diversity and environmental conditions play a role in shaping ecosystem functioning during restoration, and their importance is dependent on the function of interest. Moving forward, integrating taxonomic, functional, and phylogenetic diversity with environmental conditions while conducting and assessing restoration can aid in producing more predictable outcomes.