Graduate Thesis Or Dissertation
 

An evaluation of an inventory projection system : TRIM model predictions vs. forest inventory field measurements in North Carolina

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/rb68xf81q

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  • As part of the effort to evaluate TRIM (Timber Resource Inventory Model) for the next RPA National Assessment, a study was conducted using natural pine stands in North Carolina. TRIM has been used for regional timber supply studies in both the Pacific Northwest and the South (Southern Timber Supply Study). The model results are tools used for economic planning and policy making for regions in which timber is part of the economic base. TRIM uses yield tables arrayed by age class in the inventory projection calculations. The application of yield tables in TRIM can potentially alter the results of regional timber supply analysis. The objective of this study, is to investigate the TRIM growth mechanism and examine the effects of empirically derived yields on TRIM projections. In this process, different levels of data aggregation were compared and two other types of yield tables were developed and evaluated. Model projections were based on growth and inventory estimates derived from two successive Forest Inventory and Analysis (FIA) inventories. Simulation runs took into account "approach to normality", acreage shifts, and timber removals over the range of age classes as described by field measurements. Results were evaluated based on their comparison to FIA field measurements. In most simulations, TRIM growth and inventory projections were substantially below the growth and inventory values calculated from the Flit data. The projections varied with the yield tables used, but higher yields produced the most favorable results. For a North Carolina timber supply study, these results would indicate a sharp decline in the supply of natural pine which is the opposite of what was recorded in the field. This study suggests that empirical yield curves do not represent aggregate stand growth when stands have the characteristics found in North Carolina's natural pine.
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