Red maple dominance and community homogenization in a disturbed forested wetland

Abstract

Homogenization of forest stands with generalist species is a hallmark of past disturbance and characterizes the Great Dismal Swamp (GDS), a forested wetland in the Atlantic Coastal Plain. Once a mosaic of wetland communities, disturbances (e.g., timber harvesting and ditching) have resulted in altered hydrologic regimes and forested communities. In response, hydrologic restoration and forest management aim to enhance community composition and function. To inform these efforts, we investigated forest communities and their associations with hydrologic regimes at 79 monitoring plots across GDS, where we collected data on vegetation composition and structure, hydrologic indicators, and soil properties. Our results demonstrate that red maple (Acer rubrum) is the dominant species across GDS, where red maple importance is negatively correlated with stand density, richness, and diversity. A hierarchical cluster analysis revealed four distinct community types: Swamp Tupelo-Maple (ST-M), Maple-Holly (M-H), Sweetgum-Maple (SG-M), and Maple (M). Despite ubiquitous presence of red maple in these communities, significant differences in tree composition and structure were found; however, this variation rarely extended to other growth forms. Although water level estimates (via model simulations and high-water marks) failed to explain vegetation differences, soil properties indicative of wetness regimes suggest that communities exist along a hydrologic gradient. The ST-M community likely exists on wetter sites, whereas SG-M communities occur at drier locations. More maple-dominated communities (M and M-H; 68% of plots) likely occur across broader hydrologic gradients, explaining their widespread occurrence. These findings point to potential drivers of forested communities, but additional characterization of hydrology coupled with continued vegetation monitoring are needed to adaptively conduct hydrologic restoration efforts.