Model Solution, Validation, and Control
Solving the overall Timber Assessment Projection System entails coordination of the internal solution or computational procedures of the TAMM, NAPAP, ATLAS, and AREACHANGE modules. Our approach involves ordered solutions of the modules and iterative (Gauss–Seidel) procedures. Model validation is a critical step in model development but is particularly difficult in the present case given the size and complexity of the system. The validation process in the Timber Assessment Projection System considers the correspondence of model structure with underlying determinants, consistency with historical data, and the appropriateness of the model structure for extrapolation in policy analysis. The long (50-year) projection period and the nature of some policy scenarios can lead to values of both inputs and projected outputs that lie outside the range of historical observation. To insure “reasonable” and consistent projection behavior, a structure of model controls on capacity change and private timber harvest was implemented.
KeywordsModel Solution Capacity Change Policy Scenario Projection Period Forest Sector
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