Plant Functional Community Assembly in Grasslands and Wetlands I : Effects of Scale

Abstract

We sought to investigate how two aspects of scale (spatial extent of the species pool and grain size) influence how functional community assembly differs from random drift assembly. Theory suggests that community assembly should be increasingly random at smaller scales, but this has not been systematically investigated. We sampled plants at 18 locations along well-known moisture gradients from dry prairies to wet sedge meadows. At each location, three nested sample plots were established using three grain sizes (0.1 m^2, 1.0 m^2, 10 m^2). Four functional traits (two size traits and two leaf economics traits) were measured in every instance of each plant species. We used Monte Carlo simulations to estimate the standardized effect size of abundance-weighted mean and functional diversity using four species pool scales: regional (all species), within wet and dry habitats, within specific vegetation types, and within each stand. Weighted mean SES were consistent across both spatial extent and grain size. Spatial extent had strong, consistent effects on functional diversity. At large spatial extent, FD was strongly clustered, but it was either neutral or overdispersed at the smallest extent. Functional diversity SES were often stronger at larger grain sizes, but not in all cases.