Relative importance of risk factors for spruce beetle outbreaks

Nine factors were initially suggested by spruce beetle (Dendroctonusrufipennis (Kby.)) experts in Alaska as potentially important in determining the risk of a spruce beetle outbreak in stands. Factors suggested were stand hazard, size and trend of spruce beetle population in neighboring stands, degree–days in the past June, total rainfall in the past summer, and availability of four types of breeding material. Risk factors were organized into a hierarchical model of spruce beetle risk, and the relative importance of factors for determining risk was analyzed in three stages with the analytic hierarchy process. This process derives subjective estimates of factor importance values through a process of pair-wise comparisons. Analysis in stage 1 involved independent responses of two experts from Alaska. In stage 2, three experts from Alaska provided responses as a group. In stage 3, five experts, representing Alaska, British Columbia, and the Rocky Mountain region, provided responses as a group. In the final stage of analysis, stand hazard and windthrown trees were identified as the two most important factors determining risk of a spruce beetle outbreak. Hazard and windthrow were considered about equally important and together accounted for almost two-thirds of the total allocation of importance values among risk factors. The analytic hierarchy process is an effective method for eliciting expert knowledge and can be a useful tool for development of expert systems in natural resource management, where even expert knowledge is often incomplete.