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Although vegetation succession in the Piedmont of eastern North America favors closed-canopy forest in the absence of disturbance, historical evidence suggests upland vegetation of the region was, in near history, characterized by areas of heliophilic vegetation, such as prairies, savannas, and woodlands. While some work has been undertaken to characterize putative remnant communities at the local and subregional level, there has been no comprehensive, quantitative study to characterize the breadth of heliophilic vegetation commonly referred to as "Piedmont prairies" in the mid-Atlantic portion of the Piedmont, despite evidence that more than one community type is likely represented. We fill this gap by assessing Piedmont prairie communities in the present-day landscape using the best quantitative vegetation data currently available from the Carolina Vegetation Survey vegetation-environment database. We extracted records for 195 permanent vegetation plots representative of upland, terrestrial, open or semi-open vegetation in the Piedmont of the Carolinas and Virginia, a region coinciding with 17th- and 18th-century accounts of historical savannas. Through hierarchical clustering (flexible-β) and stride analysis (plotting the PARTANA ratio and silhouette width), we determined the optimal partition for our dataset to be 12 clusters. The R package optpart was used to move plots between clusters to further ensure plots are members of their best-fit cluster. Nonmetric multidimensional scaling ordination was used to visualize compositional trends in the dataset. We identified 12 major types of heliophilic vegetation that can be categorized into five larger groupings: Piedmont Oak-Hickory and Red Cedar Woodlands, Piedmont Glades, Piedmont Pine Woodlands, Piedmont Savannas and Grasslands, and Piedmont River Terrace Glades. [ABSTRACT FROM AUTHOR]

Narrative accounts and floristics suggest a broader historical distribution of Piedmont upland savannas and woodlands with a prairie-affinity flora than today, although dates of emergence, spatiotemporal extent, and historical dynamics remain unclear. To help address the question whether remnant prairie-affinity patches in the state represent at least historical, if not ancient, grasslands, we analyzed stable carbon isotopes from soil organic matter from two well-known localities hosting prairie-affinity heliophytes, both within the boundaries of historically mapped "Grande Savane". Soil cores for d13Corg analysis and radiocarbon dating were collected from five sites, hosting different present-day plant communities and spanning three soil orders. Recovered d13Corg values suggest historical grasslands, likely savanna-type with some fluctuations in cover, were present at both localities essentially continuously over the past 2000 years until the more recent canopy closure over the past century. These findings are consistent with historical narrative accounts, although significant additional sampling is needed to determine its spatiotemporal extent. While the general trend at our localities transitions from open to closed systems, pronounced fluctuations are apparent in all profiles, particularly between 1254-1468 CE. Precipitation does not appear predominantly responsible, but available climatic reconstructions are from an adjacent basin. The timing of the pronounced vegetation class fluctuations is intriguingly coincidental to the timing of Siouan occupancy and intertribal movements, suggesting a need for more vigorous interdisciplinary investigations. [ABSTRACT FROM AUTHOR]