Data from: 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 diversity did not vary consistently along either gradient. This did
not conform to trait variation expected under the SDH and instead
suggested that environmental filters structure tree communities throughout
both gradients, without evidence for an increased role of competition in
less stressful environments. Phylogenetic diversity of communities was
principally driven by the ratio of angiosperms to gymnosperms and
therefore did not exhibit the pattern of variation along stress gradients
expected under the SDH. We conclude that the SDH is not a general paradigm
for all eastern North American tree communities, although it may operate
in certain contexts.