Patterns and Processes of Species Diversity in Fragmented Northern Hardwood Forests.

Twenty-four upland hardwood forests were examined to determine the influence of plant dispersal and environmental heterogeneity on the composition and richness of species in the forest understory. Patterns in the dispersal attributes of established plants were evaluated in relation to associated plant traits, micro-habitats on the forest floor, and measured or inferred gradients in the availability of moisture, nutrients and light. Plant attributes that maximally explained differences in species richness were mode of dispersal, habitat affinity, life form, shade tolerance, and moisture affinity. Environmental variables that maximally explained species richness were stand structure. soil moisture and soil parent material. Species richness was strongly influenced by sugar maple abundance and declined sharply on mesic, calcium-rich soils. In this study, modes of dispersal were strongly correlated with plant traits and habitat factors that govern germination, establishment and persistence. The contribution of dispersal and environmental processes to species richness could not be distinguished, statistically