A multi-scale view of plant diversity and hydrogeomorphology in Chesapeake Bay forested wetlands

Forested wetlands trap sediment, store floodwater, and host high plant diversity. Field surveys were conducted at 15 sites at upper, middle and lower locations on six river floodplains in the Chesapeake Bay Coastal Plain Region. Objectives of this study were to: (1) measure plant species richness, woody species diversity, and hydrogeomorphic conditions in floodplain forests; (2) relate plant diversity and composition to spatial, hydrologic, and substrate conditions; and (3) evaluate these relationships at four spatial scales (plot, site, river watershed, and regional).; Major findings include: (1) species richness and Tree diversity are significantly related to and explained by hydrogeomorphic variables; (2) relationships between plant diversity and spatial and hydrogeomorphic variables vary depending on spatial scale; and (3) spatial position along the longitudinal gradient strongly impacts plant diversity and hydrogeomorphic conditions.; Species richness, tree diversity, hydrologic values, and microtopographic relief increase with downstream position. Woody species diversity (Tree H ′) shows no relationship to hydroperiod, and species richness decreased (plot scale) or showed no relationship with hydroperiod. Overall, plot-scale relationships were the least significant. Plant patterns of diversity (species richness and Tree H′) were best described at the site scale. Predictor variables for site-scale plant diversity were downstream position, micro topographic range, and hydroperiod. Hydroperiod, and microtopographic relief were explained at the watershed scale. Support for top-down hierarchy theory (but not the intermediate disturbance hypothesis) is presented as a control on plant diversity at local sites and plots.; Regional scale analyses reveal significant differences between Eastern and Western Shore sites and alluvial and blackwater sites, but variograms indicate that none of the measured variables changed as a function of spatial position alone. Environmental policy decisions require improved ways to understand the mechanics of ecological systems, tools to interpret ecological phenomena, and methods to use in decision-making that can balance economic, ecologic, and societal tradeoffs in environmental policies. This research provides potential diagnostic, speculative, and conservation tools for planning and wetland policy efforts for the Chesapeake Bay Coastal Plain.