Graduate Thesis Or Dissertation
 

Sensitivity of TRIM projections to management and stocking adjustment assumptions

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/f7623g37w

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  • The Timber Resource Inventory Model (TRIM) is a computer model used by the U.S.D.A. Forest Service in assessing the state of the Nation's forest resources and the forests' probable future conditions. TRIM is a yield table projection system designed and developed to model forest inventory changes over time in response to different levels of management and to removals from either large or small forested areas. The purpose of this study was to determine the sensitivity of regional timber availability projections to yield table assumptions and various silvicultural impacts. Yields were projected under various management assumptions. In addition, the yield projections themselves were tested by projecting yields with and without approach to normality. A literature survey was conducted to assess work previously done with changes in management assumptions, model sensitivity, and approach to normality (i.e., stocking adjustment). In the short run, the projections were constrained by current inventory, growth functions, and harvest levels. In the long run, projections were constrained by growth functions and harvest levels. Inventory projections for all species and combined ownership varied both in trend and in degree between runs in both the long and the short run. Growth trends for all species and combined ownership showed normal yields with stocking adjustment and managed yields without stocking adjustment paralleling each other in both the long and the short run. Growth for managed yields with stocking adjustment exceed the two previous management intensities in both the long and the short run. Empirical yields without stocking adjustment are far below normal yields with stocking adjustment and managed yields without stocking adjustment in the short run, but the three projections converge in the long run. It was shown that the difference between runs with and without stocking adjustment is appreciable in both the short and the long run. Limitations of TRIM include the fact that it is difficult to use for the uninitiated, harvest levels are set, and the stocking adjustment function is relatively inflexible.
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