Traditional methods of studying communities through richness and abundance struggle to identify general patterns across many ecosystems; however, recent focus on functional traits has clarified how species respond to environmental conditions. Functional traits determine ecosystem functions, such as primary productivity, so shifts in management activities that affect environmental conditions may alter functions via traits. Current assessments of functional diversity often rely on fixed trait values for species, excluding variation within species. We addressed this gap in functional ecology by examining functional diversity in restored tallgrass prairie plant communities. Restored communities differed in combinations of age, bison grazing, and prescribed fire. The functional traits plant height, leaf toughness, specific leaf area, leaf dry matter content, and plant type were measured for the ten most common species at each site and used to calculate functional richness, functional evenness, functional divergence, and functional dispersion using fixed and site-specific trait values. We examined how each functional diversity metric responded to environmental variables and how it predicted net primary productivity in each community.
Results/Conclusions
Functional evenness (FEve), a measure of evenness in species abundance through niche-space, was the only metric significantly affected by management strategies and restoration age for fixed trait values, while there were no significant effects on site-specific values. FEve increased with bison grazing, which may indicate that preferential grazing on grass species reduces grass dominance and increases evenness in species occupying other niche-space. FEve significantly decreased in older restorations, which have lower species richness in which communities lose functionally distinct species that fill gaps in niche-space. Bison grazing and prescribed fire interacted significantly with FEve, in which the increase in evenness by grazing was amplified in burn years. Combined management strategies may increase functional diversity and improve function. Lastly, net primary productivity, increased with FEve with marginal significance. Incorporating intraspecific variation into functional diversity metrics didn’t increase the predictive power of models for ecosystem function, indicating fixed trait values are suitable for functional diversity assessments in these communities. Environmental differences in these communities are driven primarily by management strategies, which may not produce strong abiotic gradients in which intraspecific variation could be greater. This study supports the use of fixed trait values for accurate assessments of functional diversity and ecosystem function.