Deterministic and stochastic factors jointly drive plant community composition and diversity in isolated wetlands

Contemporary plant communities are simultaneously the reflection of current habitat conditions and historic processes. The observed patterns in the diversity, abundance, and composition of these communities are the result of the combination of stochastic and deterministic factors. Deterministic factors such as environmental filters often leverage a greater influence in wetlands, though this may not be the case with geographically isolated communities. We evaluated the influence of environmental factors on plant community composition and richness in the Eastern Highland Rim physiographic region of the Southeastern United States. Plant communities were sampled at 27 open wetland sites. We determined that water permanence, change in water depth, grazing, and site area were important predictors of plant species richness, community composition, and the degree of stochasticity driving plant community composition. There was a negative relationship between site area and richness, and species composition was weakly correlated with geographic distance between sites. There was greater stochasticity in species composition among sites when environmental characteristics differed. The apparent influence of stochastic factors at sites appears to be dependent upon the strength of environmental filters present. This suggests that the assembly of isolated wetland plant communities may be driven first by dispersal limitations and then subsequently by environmental constraints once propagules arrive. A strong environmental filter may limit the successful colonization of new species to a site which can prevent the introduction of non-native species but inhibit restoration efforts. This has important implications for the management and conservation of imperiled wetland ecosystems.