Piedmont Alluvial Vegetation: Classification, Geographic Variation, and Restoration

Riparian ecosystems are home to diverse and highly productive plant communities, long known to be among the more species-rich terrestrial communities. However, few pristine riparian systems remain, particularly in North America. Due to their ecological significance and their current imperiled status, there is substantial interest in conservation and restoration of riparian habitat in the Southeastern United States. Successful conservation and restoration require detailed information regarding the composition and structure of natural floodplain plant communities, in addition to an understanding of the environmental drivers associated with compositional variation. While southeastern alluvial vegetation has been well-studied, most studies have focused on the larger rivers of the Coastal Plain region, rather than the relatively smaller streams of the topographically more complex inland Piedmont. In fact, there is relatively little documentation or understanding of Piedmont bottomland vegetation in North Carolina or elsewhere on the Southeastern Piedmont.;This dissertation advances our understanding of Piedmont alluvial vegetation, by documenting and describing vegetation patterns and environmental drivers in this system. This work provides the vital information that is necessary both for successful management of alluvial habitat and for restoration of degraded alluvial vegetation. As part of this work, I sampled high-quality alluvial vegetation in five North Carolina river basins: the Catawba, Yadkin-Pee Dee, Cape Fear, Neuse, and Tar-Pamlico. As a first step towards advancing our understanding of these systems, I developed a vegetation classification of the Piedmont alluvial plant communities in North Carolina. I expect this classification will provide guidance for revising Piedmont alluvial plant community concepts currently recognized in the U.S. National Vegetation Classification. I also explored the spatial distribution of plant species richness across the Piedmont riparian landscape and examined compositional variation in a metacommunity context, quantifying the relative influence of niche-processes and dispersal-processes in shaping riparian plant community composition. I found that niche-processes are dominant in this system, with environmental variables explaining more variation in community composition than spatial structure. Finally, I developed an approach for using quantitative vegetation descriptions to develop reference information for riparian restoration efforts. Because these communities are strongly structured by environmental variables, I was able to develop a matching tool to link restoration sites to described vegetation types based on environmental similarity. In all, I expect the work described in this dissertation to improve management and restoration outcomes for alluvial plant communities in the North Carolina Piedmont.