Abstract
Functional traits influence plant distributions along broad environmental gradients leading species to occupy communities where their traits enable them to successfully establish and compete for resources. Trait differences are also expected to influence plant distributions and diversity at finer spatial scales within communities. However, relatively few empirical studies have examined the extent to which interspecific trait variation predicts local species-environment distributions. We surveyed herbaceous plants within a heterogeneous acid bedrock glade in south-central Wisconsin to elucidate how traits influence local plant distributions and diversity. Using quadrat-scale environmental covariates (soil depth, canopy openness, and neighborhood tree phenology) and species functional trait means (SLA, vegetative height, and seed mass), we modeled variation in local species distributions as well as plant diversity across 361 quadrats distributed evenly in a 1 ha study plot. Functional traits predictably mediated individualistic species distributions along local gradients in soil depth and canopy openness as well as differential plant responses to variation in canopy leaf phenology. Small-seeded herbs occurred in shallow soil microsites while the prevalence of large-statured plants increased with canopy openness. Local species richness and functional trait dispersion were greatest in microsites near canopy gaps where sun-adapted and shade-adapted plant species co-occur and in microsites surrounded by later-leafing trees. Interspecific trait differences influence local species distributions and shape spatial patterns of diversity within heterogeneous plant communities like bedrock glades. The parallels between local plant distributions within this heterogeneous community and regional plant distributions across the landscape suggest trait-mediated ecological sorting influences plant distributions along environmental gradients similarly across spatial scales.
