Understanding local and regional plant diversity: Species pools, species saturation, and the multi-scalar effects of plant productivity

The different patterns of plant species diversity that occur at local to regional scales are examined across the southeastern United States. The relationship between the species pool (large-scale community diversity) and local species richness is reviewed to clarify the species pool concept and set the stage for the analyses that follow. Techniques for estimating the species pool are demonstrated using mapped ranges, county records, co-occurrence patterns, and the environmental preferences for woody species in the southeastern United States. Species pool estimates for sites across the region are then compared to the recorded plant species richness at those sites. Species pools constructed from ecological information better predict the patterns of community assembly than pools built from phytosociological data. Local versus regional richness assessments and the productivity-diversity relationship have been the subject of much debate. Local versus regional relationships are investigated for signs of community saturation and resistance to plant invasions. Community saturation is not found to be a major structuring force, but the dynamic between local and regional richness and species invasion is linked to disturbance frequency. The generality of the productivity-diversity relationship is assessed across ecologically-distinct plant communities and by using various methods for estimating plant productivity. Productivity-diversity relationships are shown to vary with respect to how local and landscape assessments of productivity are linked to richness at different scales. Collectively, this dissertation draws upon new and old techniques to link ecological processes with plant diversity patterns across the southeastern United States. Plant species diversity is revealed to be a multi-scalar phenomenon that cannot be fully addressed by local interactions alone. A set of tools and guidelines is provided to help researchers study complex relationships involving plant diversity dynamics at various scales.