Sensitivity of TRIM projections to management, harvest, yield, and stocking adjustment assumptions.

Abstract

The Timber Resource Inventory Model (TRIM) was used to make several projections of forest industry timber supply for the Douglas-fir region. The sensitivity of these projections to assumptions about management and yields is discussed. A base run is compared to runs in which yields were altered, stocking adjustment was eliminated, harvest assumptions were changed, and management intensity assumptions were changed. The objective was to determine if there is a difference in supply projections and age-class distributions in the short term (20 years) and the long term (50 years) when assumptions are changed. Changing harvest assumptions had an effect on yield projections and age-class distributions only when artificially high and low harvests were applied. Harvesting oldest age classes first had little effect on age-class distribution projections or supply projections. Changing assumptions about intensity of management and yields can have an effect on supply projections in both the short and the long term. Intensifying current management, deemphasizing harvest of older age classes, and using modified yield functions increased supply projections. The model showed that long-term volume projections decrease when future inventories are managed in the same way as current inventories. Age-class distributions were not significantly affected by changing assumptions for management and yield.

Citation

Alexander, Susan J. 1991. Sensitivity of TRIM projections to management, harvest, yield, and stocking adjustment assumptions. Res. Note. PNW-RN-502. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 20 p