Variation in Forest Canopy Composition of Riparian Networks from Headwaters to Large River Floodplains in the Southeast Coastal Plain, USA

Data on canopy trees (stems ≥ 15 cm DBH) in riparian wetlands, spanning from headwaters to large river floodplains, were used to test whether forest canopy composition differed among hydrogeomorphic (HGM) riverine subclasses and among physiographic sub-regions (Major Land Resource Areas; MLRA) within a given HGM subclass. Riverine stands (n = 225) were sampled in four MLRA regions of the Southeastern U.S. Atlantic and Gulf Coastal Plain Physiographic Provinces. Composition data were analyzed using Non-metric Multidimensional Scaling and Multiple-Response Permutation Procedures to evaluate differences among HGM subclasses and MLRA regions. Analyses showed that canopy composition differed among three a priori subclasses related to Strahler stream order: headwater complex (along 1st-3rd order streams), mid-gradient floodplain (4th-6th order), and low-gradient floodplain (> 6th order). Further, composition also differed by MLRA region within each subclass. Thus, not only was species composition related to riverine hydrogeomorphology across a wide physiographic area, but differences in composition within HGM subclasses were also related to sub-region. These data could be useful in defining floristic reference standards when evaluating floodplain condition in southeastern USA Coastal Plain stream networks.