Ditching, drainage, and conversion to agriculture or other uses caused the historical loss or deterioration of many depressional wetlands. In addition, some regulatory protections against converting these "isolated" systems have been removed. Therefore, conserving intact depressions and restoring degraded sites are issues that concern land managers, wildlife biologists, and citizens interested in preserving native habitats. Restoring degraded wetlands to more natural functioning can enhance multiple ecosystem services on the landscape. In addition to providing biological diversity and wildlife habitat, these wetlands can function in water storage and water-quality improvement.

Hydrology (the behavior of water in a system), soils, and plants help to define a wetland. It can take a long time to change soil characteristics, but altering hydrology by ditching can cause rapid change because many wetland species cannot survive in a drained area. This makes reestablishing natural water levels critical for restoring a wetland. Diane De Steven, research ecologist at the SRS Center for Bottomland Hardwoods Research in Stoneville, MS, is working with other researchers at the Savannah River Site, SC, to find ways to restore depressional wetlands and to manage the process in a cost-effective manner. One of these is the Carolina Bay Restoration and Banking Project, which is coordinated by University of Kentucky forest hydrologist Chris Barton, a former member of the SRS Center for Forested Wetlands Research in Charleston, SC. "We took on quite a large experimental project," says De Steven. "We attempted to rehabilitate 16 drained wetland sites simultaneously by clearing out successional vegetation and blocking the drainage ditches. We've followed their progress for 5 years now, and it's taken a lot of work by many dedicated people."

De Steven's research focuses on ways to establish appropriate wetland plants in the restored depressions. She began the work while stationed at the Charleston unit, and she collaborates with partners from the Savannah River Ecology Laboratory and the University of Kentucky. In addition to hydrology, water quality, and plant studies, other research teams (including one led by SRS wildlife biologist John Kilgo) are looking at how different animal groups are responding to the restorations.

De Steven's research team asked whether bringing back wetland plant species to the restored sites could be accomplished simply through the natural processes of germination from seed banks and seed dispersal, or whether supplemental plantings are needed. "If hydrologic conditions recover well and wetland plants can establish naturally, then some costs of restoration could be reduced," she points out. Researchers found that the experimental wetlands quickly developed a good cover of herbaceous wetland plants that germinated from the seed banks; however, some key species weren't found in the seed banks and didn't colonize naturally, so the team did additional experiments to show that selected wetland tree and grass species could be planted successfully.

De Steven cautions that their findings may not apply to all situations where depressional wetlands have been degraded. "We believe that these restoration sites were reasonably successful because, even though they had been drained in the past, they are located within managed forests with other nearby wetland habitats to act as seed sources. If you were trying to restore drained depressions on farmlands, it's possible that the seed banks might not have suitable wetland plant species. In that case you would certainly have to plant, assuming that you could restore favorable hydrology."

The project encountered some unexpected challenges. "The year we started the restorations, the whole region was heading into a severe drought that lasted several years. That was unlucky for getting natural hydrology established quickly, but we learned other things from seeing how the wetlands responded."

For more information:
Diane De Steven at 662–686–3602 or ddesteven@fs.fed.us.