Simulating Mortality From Forest Insects and Diseases

We describe methods for incorporating the effects of insects and diseases on coniferous forests into forest simulation models and discuss options for including this capability in the modeling work of the Interior Northwest Landscape Analysis System (INLAS) project. Insects and diseases are major disturbance agents in forested ecosystems in the Western United States, and over time, are responsible for major changes in forest composition and structure. Incorporating their effects into forest simulation models is difficult, especially the representation of large, episodic insect epidemics. Much empirical data on insect mortality is available for modelers, and an array of mortality models have been incorporated into indivdual tree growth simulators. Scaling these models to simulate epidemics on landscapes requires, among other things, parameters that describe the amplitudes and periodicities of pathogen/pest population cycles. Incorporating insect and disease effects into forest simulation models makes it possible to explore ways to minimize epidemic conifer mortality and secondary interactions with other disturbances. In addition, the inclusion of other resource goals and financial considerations makes it possible to analyze the costs and benefits of forest management activities that target stands with high risk of mortality. We discuss options for modeling insect and disease mortality within the INLAS project.