EXTRAPOLATION PROBLEMS IN MODELING FIRE EFFECTS AT LARGE SPATIAL SCALES - A REVIEW

Models of vegetation change in response to global warming need to inco rporate the effects of disturbance at broad spatial scales. Process-ba sed predictive models, whether for fire behavior or fire effects on ve getation, assume homogeneity of crucial inputs over the spatial scale to which they are applied. Landscape disturbance models predict final burning patterns, but either do not model mechanistic behavior and exp licit spread rates, or require large amounts of data to initialize sim ulations and predict ecological effects. Empirical data on the ecologi cal effects of fire are not generally available at these scales, and c onclusions are often extrapolated upward from stand-level data. Three methods for extrapolating ecological effects of fire across spatial sc ales and the sources of error associated with each were identified: (1 ) extrapolating fire behavior models directly to larger spatial scales ; (2) integrating fire behavior and fire effects models with successio nal models at the stand level, then extrapolating upward; and (3) aggr egating model inputs to the scale of interest. Extreme fire events pre sent a challenging problem for modelers, regardless of which extrapola tion method is employed. No single approach to modeling fire effects i s inherently superior; modeling objectives and the characteristics of specific systems will determine the best strategy for each situation.