Tree plantings in depression wetland restorations show mixed success (South Carolina)
Studies of bottomland forest restoration in the southeastern United States indicate that success can be improved by protecting planted tree seedlings from herbivores and controlling competing vegetation. Reforesting “isolated” depressional wetlands may present different challenges: growing-season ponding may expose seedlings to flooding stress, and competition control may be undesirable because developing herbaceous cover is often a restoration goal in these wetlands. We evaluated a low-effort approach for reforesting degraded Coastal Plain depressions with wetland tree species. In eight wetlands that were restored by clearing out successional vegetation and plugging drainage ditches, we planted seedlings of swamp tupelo (Nyssa biflora) and baldcypress (Taxodium distichum) in alternating rows at 15-ft (5-m) spacing. Heights at planting averaged 22 inches (0.5 m) and 41 inches (1 m), respectively. After four years, survival averaged 79 percent for baldcypress, but only 23 percent for tupelo. Most tupelos died during the first two years, likely from a combination of flooding followed by drought stress and competition from emergent vegetation. After four years, average height of baldcypress was 55–98 inches (140–250 cm), while tupelo averaged 28–70 inches (70–170 cm). Baldcypress was successfully established with little effort, whereas the tupelo appeared more sensitive to ponding conditions. Existing guidelines for bottomland forest restoration recommend a minimum tree seedling height of 18 inches (46 cm). However, in depressional wetlands that are ponded during the growing season, using taller seedlings or preferentially planting into shallow-water zones may improve survival.