H.L. Allen

Manipulation of water and nutrients - practice and opportunity in southern U.S. pine forests.

Abstract 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.

The influence of nutrient and water availability on carbohydrate storage in loblolly pine

We quantified the effects of nutrient and water availability on monthly whole-tree carbohydrate budgets and determined allocation patterns of storage carbohydrates in loblolly pine (Pinus taeda) to test site resource impacts on internal carbon (C) storage. A factorial combination of two nutrient and two irrigation treatments were imposed on a 7-year-old loblolly pine stand in the Sandhills of North Carolina. Monthly collections of foliage, branch, stem, bark, and root tissues were made and total non-structural carbohydrate analyses were performed on samples collected in years 3 and 4 after treatment initiation. Seasonal fluxes of carbohydrates reflected the hypothesized use and storage patterns. Starch concentrations peaked in the spring in all tissues measured; however, minimum concentrations in aboveground tissue occurred in late winter while minimum concentrations in below ground tissue occurred in late fall. Increased nutrient availability generally decreased starch concentrations in current year tissue, while increasing starch in 1-year-old woody tissue. Irrigation treatments did not significantly impact carbohydrate flux. The greatest capacity for starch storage was in below ground tissue, accounting for as much as 400 kg C/ha per year, and more than 65% of the total stored starch C pool. The absolute amount of C stored as starch was significantly increased with increased nutrient availability, however, its relative contribution to the total annual C budget was not changed.