Influences of management of Southern forests on water quantity and quality

Abstract

Water is a key output of southern forests and is critical to other processes, functions, and values of forest ecosystems. This chapter synthesizes published literature about the effects of forest management practices on water quantity and water quality across the Southern United States region. We evaluate the influences of forest management at different temporal and spatial scales, and we recognize the heterogeneity of forest ecosystems; e.g., wetlands and uplands in the South. Hydrologic models that were developed specifically for southeastern forests were reviewed. We conclude that the greatest streamwater yield or ground-water table changes occur immediately following forest land disturbances. The overall water-quantity impact of silvicultural operations on wetlands is much less than in areas having greater relief and shallow soils. Water quality from forested watersheds is the best when compared to that from other land uses. Silvicultural practices in the South caused relatively minor water-quality problems. Roads without best management practices (BMP) are the major source of sedimentation. Studies on the cumulative effects of land use changes on water quality are lacking. Exiting computer modeling tools are useful but limited in describing the forest hydrologic processes and providing practical guidance in designing forest BMPs. Recommendations to future research on forestry BMPs and forest hydrology in general are proposed. INTRODUCTION Water is a key output of southern forests and is critical to other processes, functions, and values of forest ecosystems. Most of the drinking water in the South comes from forested watersheds. Much of our current understanding of the linkages between southern forest management and water quantity and quality is derived from long-term watershed-scale experiments conducted in more than 140 small watersheds in various physiographic regions in the 13 Southern States (Chang 2002). This chapter synthesizes published literature about the effects of forest management on water quantity and water quality across the region. We evaluate the influences of forest management at different temporal and spatial scales. We recognize the heterogeneity of forest ecosystem, e.g., wetlands and uplands, as affected by climate, geology, and topography. We identify sensitive regions and discuss the effects of management activities on the timing of hydrologic responses across the physiographic regions of the South. We scale up information derived from experiments at field and watershed scales to the regional level. Forest management practices examined in this chapter include harvesting, site preparation, bedding, surface drainage, road building, fertilizer and herbicide applications, and fire management. A review of regional hydrologic characteristics across nine physiographic regions is used as a framework to contrast effects of various management practices on key waterquantity and water-quality variables. Hydrologic models that were developed specifically for southeastern forests are reviewed. 1 Research Hydrologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Raleigh, NC 27606; Research Hydrologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Otto, NC 28763; Associate Professor, University of Georgia, Warnell School of Forest Resources, Athens, GA 30602; Research Soil Scientist, U.S. Department of Agriculture Forest Service, North Central Research Station, Grand Rapids, MN 55744; Research Hydrologist, U.S. Department of Agriculture Forest Service, Southern Research Station, Charleston, SC 29414; and Sustainable Forestry Program Manager, National Council for Air and Stream Improvement, Newberry, FL 32669, respectively. So ut he rn F or es t Sc ie nc e: Pa st , P re se nt , a nd F ut ur e W at er a nd S oi ls 196