MANIPULATION OF WATER AND NUTRIENTS - PRACTICE AND OPPORTUNITY IN SOUTHERN UNITED-STATES PINE FORESTS

The magnitude and duration of response of southern pine forests to operations silvicultural treatments including site preparation, drainage, bedding, weed control, thinning, and fertilization are reviewed. The current information for making silvicultural prescriptions in the southeastern U.S. has been developed largely from empirical trials. Silvicultural research has provided only a rudimentary understanding of how water and nutrient availability is altered through silviculture and how they influence stand productivity. Research indicates that many southern pine stands have leaf areas that are below what is theoretically considered to be optimal for maximum productivity. Leaf-area development appears to be limited by both nutrient and water availability. Few data are available to assess the role of changes in resource availability on leaf-area development, photosynthetic efficiency, carbon allocation, and growth attributable to silvicultural treatments. A conceptual model outlining the expected influence of silvicultural treatments on nutrient and water availability and thus on leaf-area development, carbon fixation, carbon allocation and stemwood production is proposed. Blending empirical information with a conceptual understanding of forest productivity should aid in developing silvicultural prescriptions that will help to ameliorate water and/or nutrient limitations, resulting in increased productivity. Major challenges impeding rapid application of existing technology are (1) lack of awareness of opportunities to increase productivity, (2) inadequate capital for silvicultural investments due to uncertainty of the long-term supply and value of wood, and (3) infrastructure barriers that slow the acceptance and implementation of new silvicultural techniques. Future research needs to focus on testing and quantifying the conceptual relationships described, as well as developing practical techniques to assess water and nutrient availability in forest stands. © 1990.