Box 6.4 Bottomland Hardwood Wetland Restoration In The Mississippi Drainage
At the time of European settlement, approximately 80 million hectares of forested wetlands existed in the conterminous United States. By the mid-1970s, this area had been reduced to about 24.4 million hectares (Gosselink and Lee, 1989). Drainage, logging, and conversion to agriculture accounted for most of the losses, especially in the Mississippi floodplain, where 78 percent of the forested wetlands have been lost (MacDonald et al., 1979). Clearing for cotton fields was extensive in the early 1800s. In the 1920s, following major floods, congressional actions began to increase federal flood control project construction in the lower Mississippi River valley. River channelization and flood control structures altered the natural hydrologic regimes of vast floodplain areas. Further conversion for soybeans has had substantial impacts on the bottomland hardwood resource in recent decades, as have urbanization and industrial development.
The drained and converted agricultural lands of the Mississippi floodplain retain the natural alluvial soils; it is the hydrology that has been greatly altered. In these cases, restoration of large areas could be initiated by halting row crop planting and other farmland activities and by closing drainage ditches and small canals. In many areas, the clay soils retard drainage and hold sufficient moisture, so that wetland vegetation would become reestablished. Planting of wetland forest species can accelerate the return to a bottomland forest. It is not realistic, however, to anticipate that true restoration to the original geologic, hydrologic, and biological conditions is possible except in very limited areas.
Most bottomland forest restoration projects focus on techniques of planting and establishing forest species (i.e., reforestation). Restoration success is commonly judged, at least in the early phases, by the success of tree seedling establishment, and increased timber values and wildlife habitat are often the major goals. Typicalcosts of direct seeding in 1989 were about $40 to $60 per acre (Allen and Kennedy, 1989); planting seedlings costs two or three times as much. The most successful technique is to plant mixtures of species in blocks or rows. This approach enhances the establishment of species that grow more slowly and compete poorly.
A small number of restoration projects have come under the Conservation Reserve Program. Most of these projects began during the late 1980s. Although some may appear promising in terms of species composition and structure, it is too soon to assess the recovery of other wetland functions.