Vegetation of Upper Coastal Plain depression wetlands: Environmental templates and wetland dynamics within a landscape framework

Abstract

Reference wetlands play an important role in efforts to protect wetlands and assess wetland condition. Because wetland vegetation integrates the influence of many ecological factors, a useful reference system would identify natural vegetation types and include models relating vegetation to important regional geomorphic, hydrologic, and geochemical properties. Across the U.S. Atlantic Coastal Plain, depression wetlands are a major hydrogeomorphic class with diverse characteristics. For 57 functional depression wetlands in the Upper Coastal Plain of South Carolina, we characterized the principal vegetation types and used a landscape framework to assess how local (wetland-level) factors and regional landscape settings potentially influence vegetation composition and dynamics. Wetland sites were stratified across three Upper Coastal Plain landscape settings that differ in soils, surface geology, topography, and land use. We sampled plant composition, measured relevant local variables, and analyzed historical transitions in vegetative cover types. Cluster analysis identified six vegetation types, ranging from open-water ponds and emergent marshes to closed forests. Significant vegetation-environment relationships suggested environmental "templates" for plant community development. Of all local factors examined, wetland hydrologic regime was most strongly correlated with vegetation type, but depression size, soil textural type, and disturbance history were also significant. Because hydrogeologic settings influence wetland features, local factors important to vegetation were partly predictable from landscape setting, and thus wetland types were distributed non-randomly across landscape settings. Analysis of long-term vegetation change indicated relative stability in some wetlands and succession in others. We developed a landscape-contingent model for vegetation dynamics, with hydroperiod and fire as major driving variables. The wetland classification, environmental templates, and dynamics model provide a reference framework to guide conservation priorities and suggest possible outcomes of restoration or management.

Ecological Outcomes and Evaluation of Success in Passively Restored Southeastern Depressional Wetlands

“…Annual hydroperiods (ponding durations) differ intrinsically among wetlands and also between years, becoming progressively shorter during droughts (Mulhouse et al 2005;Stroh et al 2008). What controls the inherent hydroperiod capacity of individual depressions is not fully understood, but likely factors include basin geomorphology, topographic position, and soil type (De Steven and Toner 2004).…”

“…The depressions were forested with vegetation that was hydrophytic (meeting wetland jurisdictional criteria; ACOE 1987) but dominated by facultative (FAC) tree species indicative of prior drainage (e.g., sweetgum, Liquidambar styraciflua; loblolly pine, Pinus taeda; water oak, Quercus nigra). Disturbed depressions with this forest composition are often shorthydroperiod basins with ponding (if any) mainly in the dormant season (De Steven and Toner 2004). The study sites were still draining from surface ditches when the study began (Barton et al 2008).…”

“…For example, if restored hydroperiod is not predictable, a desired vegetation type could be incompatible with a wetland's hydrologic capacity to support it. The issue is especially pertinent to depressional wetlands, whose plant communities are structured by seasonal hydroperiods that differ inherently with depression geomorphology and other factors (Kirkman et al 2000;De Steven and Toner 2004;Casey and Ewel 2006).…”

“…Accordingly, the 16 wetlands had been assigned randomly to approaches for achieving either of two "target" vegetation types (herbaceous or wet forest), and to alternative systems for managing upland forest buffers (unmanaged, or thinned and periodically burned). The targets and management options were based partly on state-change models for plant community types (aquatic, herbaceous, and forested) in Southeast depressional wetlands (Kirkman 1995;De Steven and Toner 2004). Of particular interest was whether hydrology restoration and forest removal alone could supply conditions favorable to establishing the herbaceous vegetation type.…”

Evaluating Cumulative Ecosystem Response to Restoration Projects in the Lower Columbia River and Estuary, 2009

“…Welcomme (2008) advocates the use of maximum area flooded over the course of a year as the best predictor of fish production, which for very large rivers such as the Amazon can be quantified using remote sensing methods. The coefficient of variation of mean monthly water depth over the 8-month growing season, which indicates the relative fluctuation of water levels and ponding duration, was a good predictor of vegetation type in coastal depressional wetlands (De Steven and Toner 2004). Methods range from the complex and expensive, e.g., hydrodynamic modeling (Silvestri et al 2004), to the simple, e.g., the number of months per year during which standing water is present, as observed during monthly visits to the site (Meyer et al 2008).…”