The role of a stand dynamics model in the spruce budworm decision support system

Stand dynamics models that predict effects of pests on forest development are key components of pest and forest management planning decision support systems (DSS). Such stand models are required to quantify the marginal effects and costs-benefits of alternative strategies, and thereby to assist in evaluating management options and defining tactics and strategies. The spruce budworm (Choristoneura fumiferana (Clem.)) DSS allows users to project forest inventories under alternative budworm and protection (insecticide use) scenarios, to plan protection programs based on marginal timber supply benefits, to incorporate budworm effects on stand or forest development into management plans, and to evaluate silvicultural and forest management alternatives to limit damage. The STAMAN Stand model is an integral part of the spruce budworm DSS, used to calculate stand impact matrices used by two DSS components. Simulations, using STAMAN, for 13 classes of spruce-fir stands under various levels of constant, cumulative defoliation for a 10-year period, resulted in predicted volume reductions of 1-6% with 20% defoliation, 27-42% with 60% defoliation, and 82-99% with 90% defoliation. Another set of simulations using a 30-year cyclical defoliation pattern (including 5 years of light defoliation, 8 years of moderate-severe defoliation, and 17 years of very light or nil defoliation) resulted in volume reductions similar to published data for actual spruce budworm outbreaks.