Optimizing Nutrient and Timber Management for the Town of Butner, NC

Abstract

The following report documents the findings of a client-focused group Master’s Project completed at the Nicholas School of the Environment at Duke University. The project’s purpose is to support the client’s goal to optimize nutrient and timber management in a 750-acre forested tract owned by the Town of Butner in Granville County, North Carolina. Excess nitrogen and phosphorus delivery to drinking water reservoirs has become a concern in the North Carolina piedmont as development pressure increases in surrounding watersheds. The Falls Lake Nutrient Strategy is among several new regulations aimed at reducing nitrogen and phosphorus delivery to an increasingly eutrophic public water supply. While the regulation pressures upstream communities to reduce their impact, mitigation strategies are diverse and can be costly to local governments. Even though a market-driven nutrient trading credit system is included in the Falls Lake Nutrient Strategy, there is currently no opportunity to earn credits through avoided deforestation or land conservation, commonly called “conservation credits”. The Town of Butner is interested in novel approaches to managing its nutrient loading and the possibility of earning conservation credits while managing its forestland for timber. There were four objectives to this project, 1) to estimate the value of timber on the property, 2) to determine the range of impacts that different timber management scenarios will have on nitrogen and phosphorus loading from the property, 3) to develop a simple tool that land managers can use to predict optimal outcomes for different timber and nutrient management scenarios, and 4) to inform state policy on the value of conservation credits and the effects of forest management on nutrient loading. A range of forest management scenarios with different harvest practices and maintaining 50-ft to 200-ft streamside management zones were modeled over a 30- year timeline. The USDA Forest Service’s Forest Vegetation Simulator (FVS) and Timber-Mart South were used to project harvested and standing timber values under each scenario. GIS-based models were employed to predict nitrogen and phosphorus delivery to perennial and intermittent streams under each scenario. The future value of conservation credits was assumed to be the sum of the value of nitrogen and phosphorus credits in the existing NC Department of Environment and Natural Resources, Nutrient Offset Program. The findings of this project suggest that the monetary value of timber within the 50-ft to 200-ft buffer zone far exceeds any reasonable economic value of conservation credits earned by not harvesting within the buffer zone during a 30-year time horizon. Timber harvesting, and in particular changing the buffer zone width from 50-ft to 200-ft, had a relatively small impact on nitrogen and phosphorus loading when compared to other land uses. The implication is that nutrient management and productive forest management are not mutually exclusive. The minimum buffering requirement of 50-ft was effective at removing nutrients, while still permitting the maximization of timber revenue.