Using trait and phylogenetic diversity to evaluate the generality of the stress-dominance hypothesis in eastern North American tree communities

The stress-dominance hypothesis (SDH) is a model of community assembly predicting that the relative importance of environmental filtering increases and competition decreases along a gradient of increasing environmental stress. Tests of the SDH at limited spatial scales have thus far demonstrated equivocal support and no prior study has assessed the generality of the SDH at continental scales. We examined over 53 000 tree communities spanning the eastern United States to determine whether functional trait variation and phylogenetic diversity support the SDH for gradients of water and soil nutrient availability. This analysis incorporated two complementary datasets, those of the U.S. Forest Service Forest Inventory and Analysis National program and the Carolina Vegetation Survey, and was based on three ecologically important traits: leaf nitrogen, seed mass, and wood density. We found that mean trait values were weakly correlated with water and soil nutrient availability, but that trait d...