A Drawdown Flora in Virginia

ABSTRACT
Species composition and relative dominance (cover) were documented in an emergent macrophyte community on recently exposed sediment during an artificial drawdown of a large reservoir in the Coastal Plain of Virginia. Observations included nine county records (New Kent County), four of which were records for the Lower Peninsula of Virginia and are considered state rare species. Dominance calculations by distance class (five-meter increments from the original shoreline to the existing waterline) showed that certain species were locally dominant near the original shoreline (e.g., Fimbristylis autumnalis), whereas others, particularly the state rare species, were more prevalent near the drawdown waterline (e.g., Lipocarpha micrantha). These results suggest that the timing and magnitude of drawdown events may influence recruitment of the species observed in this study. These species appear to form seedbanks in the substrate of the reservoir for long periods of time, and are capable of rapid germination and regeneration (seed set) during short-lived, unpredictable drawdown conditions. Small seed size and other environmental factors accommodate a predisposition to this “temporal” niche. Based on this research and the work of others, we suggest that such species are part of a regional “drawdown flora.”