SPECIAL FEATURE: VEGETATION SURVEY Classification and description of alluvial plant communities of the Piedmont region, North Carolina, USA

Questions: What are the alluvial vegetation types of the North Carolina Piedmont? How is species composition related to site conditions? Location: Catawba, Yadkin-PeeDee, Cape Fear, Neuse and Tar-Pamlico River Basins, North Carolina Piedmont region, southeast USA. Methods: We recorded 194 alluvial vegetation plots. Vegetation types were derived using flexible b-hierarchical cluster analysis and random forests classifiers to reassign misclassified plots. We used canonical correspondence analysis to show the relationship between species composition and key environmental variables. Results: Twelve forested vegetation types and two herbaceous types were distinguished, nested within a hierarchical classification structure of five higherlevel groups. The five mega groups describe broad geomorphic‐floristic conditions, whereas the narrower vegetation types characterize finer-scale floristic variation. Floristic variation is related to stream order and soil chemistry (pH and Ca:Mg ratio), as well as soil texture variables (percentage sand and percentage clay). We present a summary of floristic composition and structure, environmental setting and geographic distribution for each of the 14 vegetation types. Conclusions: We suggest recognition of 14 alluvial vegetation types in the North Carolina Piedmont. In comparing our vegetation types with the community concepts currently recognized in the US National Vegetation Classification, some of our types fit well within recognized NVC associations, whereas others deviate sharply from established types, suggesting the need for reworking the currently recognized NVC alluvial type concepts.