The Douglas-fir Beetle Impact Model (DFBIM), an extension to the Forest Vegetation Simulator (FVS), simulates the epidemic impacts of Douglas-fir beetle (Dendroctonus pseudotsugae Hopk.) on its principal host, Douglas-fir (Pseudotsugae menziesii). Douglas-fir beetle typically operates as a subtle component in western forests throughout the range of Douglas-fir, but the endemic level of the beetle is not addressed in this model. Accelerated mortality of large diameter Douglas-fir along with dominant and co-dominant Douglas-fir is the main impact of Douglas-fir beetle represented by this model. No height or diameter growth reductions are imposed.
A successfully attacked tree of large diameter attracts additional beetles that will likely have success in raising brood. The resultant beetle populations can put the stand in an outbreak condition and generate high Douglas-fir mortality. Wind-thrown trees of sufficient size are also initiators of outbreaks due to the successful brood that can occur in them. DFBIM contains a windthrow model for representating windthrow events. The probability of an area-wide outbreak and the probability that any particular stand will be involved in such an outbreak is determined through user-controllable parameters.
The continuation of an ongoing outbreak can also be accommodated in the model. When Douglas-fir beetle damage codes are present in the inventory tree list, tree mortality from an outbreak in progress can be initialized from these damage codes.
The original model source code and user's guide (Marsden et al. 1994) were co-authored by Michael A. Marsden, Bov B. Eav, and Matthew K. Thompson. Except for code modifications necessary to maintain consistency with FVS and meet requirements of compilers and platforms, the model has not been altered from its original specifications.
Marsden, Michael A., Bov B. Eav, and Matthew K. Thompson. 1994. User's Guide to the Douglas-fir Beetle Impact Model. General Technical Report RM-250. Fort Collins, CO: U.S. Department of Agriculture, Forest Service.