Vegetation changes and land-use legacies of depression wetlands of the western coastal plain of South Carolina: 1951–1992

Abstract

We examined historical patterns of land use of depression wetlands (Carolina bay and bay-like wetlands) to determine if a relationship between vegetative successional changes over a 41-year period and previous human disturbances (primarily agricultural) could be established. Land cover was interpreted from 1951 (black and white) and 1992 (false color infrared) aerial photography of the Savannah River Site (a 780 km 2 federal nuclear facility in which wetlands have been relatively undisturbed since 1951). Patterns of change from one land cover to another were detected by constructing a series of frequency tables. About one fourth of the 299 wetlands identified were either pasture or cultivated in 1951, and the majority had been ditched for drainage. Agriculturally disturbed wetlands primarily became mixed hardwood/pine or were converted to pine plantations by 1992; however, no successional differences between wetlands that were cultivated versus pasture were detectable. The type of land use of many of the depression wetlands prior to 1951 probably was determined by physical characteristics of the wetlands (e.g., topographic position, size, and hydrologic features). Thus, in many cases, separation of recovery trajectories from other successional pathways, initial hydrogeomorphic differences, and/or continued human influences is not possible in this study. However, from this change-detection study, we recognize that many of the currently protected depression wetlands at SRS were disturbed by agricultural practices or were impacted by hydrologic alterations prior to t951, implying considerable resilience in the recovery toward a functioning wetland condition if hydrologic regimes are restored. A significant finding of this study is the relative stability of herb-dominated bays, which indicates that this vegetation type is not necessarily a successional continuum toward an eventual hardwood forest, at least in the temporal scale of the study. Thus, we suggest that management prescriptions for the restoration/conservation of herb-dominated wetlands should incorporate concepts of temporal stability within a framework of cyclical hydrologic and vegetation changes.

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

“…Agricultural land use ended when the SRS was established in 1951, and the farmed uplands were reforested to southern pines. Altered wetland depressions reverted by natural succession to various vegetation types, depending upon the extent to which remnant ditches ceased to drain and ponding regimes recovered (Kirkman et al 1996). The regional climate is humid subtropical, with mean annual rainfall of 1,200 mm, a long growing season, and periodic multi-year droughts.…”

SRS Ecology Environmental Information Document

“…Shields et al (1982) reported that approximately 199 Carolina bays exist on SRS, and Mackey et al (1985) indicated that wetlands cover more than 21% of the site. More recently, Kirkman et al (1996) increased that count to 299 Carolina bays and bay-like depressional wetlands. The primary wetland cover types summarized in are bottomland hardwood forest, cypress-tupelo swamp forest, scrub-shrub areas, emergent marsh, and open water.…”

“…The identification number, name, location, wetland surface area, and habitat type of each bay are presented in Locations and Areas of Ponds and Carolina bays at the Savannah River Plant (Shields et al 1982). A more recent survey by Kirkman et al (1996) identified 299 Carolina bays and bay-like wetlands on SRS (Figure 5-23). …”

“…A project to restore degraded Carolina bays on SRS was undertaken to serve as the initial "deposit" in The Bank. Over 300 Carolina bays or bay-like depression wetlands occur on the SRS, of which an estimated two-thirds were ditched or disturbed prior to federal occupation of the Site (Kirkman et al 1996). Historical impacts to the Carolina bays at SRS were primarily associated with agricultural activities.…”

The Carolina Bay Restoration Project - Final Report 2000-2006.

“…Based on information and techniques gained from previous research on Carolina bay wetlands (USDOE 1997, Singer 2001, a project to restore degraded Carolina bays on the SRS was undertaken to serve as the initial "deposit" in The Bank. There are 343 Carolina bays or bay-like depression wetlands on the SRS, of which an estimated two-thirds were ditched or disturbed prior to federal occupation of the Site (Kirkman et al, 1996;. These isolated wetlands range from small ephemeral depressions to large semipermanent ponds of 10-50 hectares in size.…”