Plant Community Response to Hydrologic Restoration in the Great Dismal Swamp

ABSTRACT Peatlands in the mid-Atlantic outer coastal plain region contain obligate hydrophyte species which were harvested and replaced by facultative tree species. The Great Dismal Swamp was drained from the colonial era until 1974, when water levels were partially restored. In September 2013, further restoration consisting of two large weirs followed extensive peat-burning fires. This study evaluated depth-to-water-table and vegetation structure both prior to and following weir operation. Wells were installed and depth-to-water-table was recorded continuously from 2013 to 2015 within six of the 15 forested stands where vegetation species dominance was quantified for tree, shrub, herb, and vine strata. Following weir installation in 2013, water tables rose an average of 28.08 cm in 2014 and 32.69 cm in 2015, during the June–July peak of the growing season. Most water levels were too low to meet the federal regulatory indicator of wetland hydrology or the seasonally flooded, saturated hydrologic regime typical of peatlands. After restoration, species dominance and frequency, as well as metrics based on hydrophyte dominance and floristic quality in study plots, were unchanged. Ordinations detected no directional shift in plant community composition among pre- and post-weir periods. Although insufficient time may have passed for shifts in plant communities, additional increases in water level above those reported here appear necessary to restore a pre-disturbance hydrologic regime and plant community structure. However, above some threshold water level, planted trees will exhibit increased mortality and limit reestablishment.