The effects of forest management intensity on carbon storage and revenue in Western Washington: A model and Monte Carlo-based case study of tradeoffs at Pack Forest

Abstract

Forest C offsets allow payments to forest owners who improve carbon (C) uptake and storage. I quantified the amount and value of C under different intensities of management practices at Pack Forest in the western Cascade Mountains, Washington using forest inventory data and results from the Forest Vegetation Simulator (FVS) forest growth simulation model. First, differences in C storage were analyzed among eight forest management scenarios over 30-years using multi-objective optimization. Management scenarios included clearcutting in 45-year intervals, Forest Stewardship Council Pacific Coast Standards with 65- and 105-year interpretations of culmination of mean annual increment (cMAI), a thinning regime, and no management. Greater harvest intensity resulted in less C storage, and C in wood products did not make up for harvest losses. At the whole-forest scale, no significant differences in C storage occurred among the five most intensive scenarios, ranging from FSC 105-year cMAI to clearcutting in 45-year rotations. FSC scenarios stored more C than clearcut scenarios within conifer stands in the first 0-30 years following harvest. Differences diminished as stands aged. FSC optimization resulted in a majority of stands harvested before cMAI. Second, net-present-values (NPVs) of clearcutting in 45- and 65-year rotations and no management scenarios were calculated using both timber and C credits for revenue over 40- and 100-years. Carbon mass and harvested board-feet were modeled using average values for age-class-productivity strata derived from forest inventory and FVS model results. Carbon credits were calculated following an American Carbon Registry methodology. Monte Carlo simulations modeled uncertainty in NPV including FVS model error and future prices for timber and carbon credits. Scenarios of increasing C credit price were also conducted. The risk of losing money increased with less intensive management. Forest C projects became more profitable on average as the price of C credits increased, but the probabilities of both large profit and large loss also increased. An average C credit price of $49.87 was required for clearcutting in 65-year rotations and $73.82 per C credit for no management to equal the mean NPV from timber obtained through clearcutting in 45-year rotations. FVS model error contributed more than 70% to variance in NPV results, raising questions on its utility in forest C projects.