The Western Spruce Budworm (WSB) Damage model, an extension to the Forest Vegetation Simulator (FVS), predicts topkill, height growth, diameter growth, and tree mortality impacts of western spruce budworm (Choristoneura occidentalis Freeman) defoliation on its spruce and fir host tree species (Crookston 1991). This model is formed from two components of the Western Spruce Budworm Modeling System (Sheehan et al. 1989, Crookston et al. 1990): foliage dynamics and damage. The complete modeling system represented complex budworm population dynamics, but is no longer in service.
The damage model allows users to specify defoliation patterns by tree species, size class, crown third, and needle age class (Crookston et al. 1990). There are three size classes and four foliage age classes defining the foliage/defoliation patterns for each budworm host species. The damage model is not responsive to changing stand conditions and requires users to make detailed predictions about defoliation patterns for the entire simulation period. For the user's evaluation of the specified defoliation patterns, there are two output tables available: a cumulative damage summary and periodic damage tables at each FVS cycle boundary, displaying the results of budworm defoliation on FVS model trees.
Crookston, Nicholas L., J.J. Colbert, Paul W. Thomas, Katharine A. Sheehan, and William P. Kemp. 1990. User's guide to the western spruce budworm modeling system. Gen. Tech. Rep. INT-274. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 40 pp.
Crookston, Nicholas L. 1991. Foliage dynamics and tree damage components of the western spruce budworm modeling system. Gen. Tech. Rep. INT-282. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station. 40 pp.
Sheehan, Katharine A., William P. Kemp, J.J. Colbert, and Nicholas L. Crookston. 1989. The western spruce budworm model: structure and content. Gen. Tech. Rep. PNW-Gtr-241. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 70 pp.