Probability of infestation and extent of mortality associated with the Douglas-fir beetle in the Colorado Front Range

Infested and uninfested areas within Douglas fir, Pseudotsuga menziesii (Mirb.) Franco, stands affected by the Douglas-fir beetle, Dendroctonus pseudotsugae Hopk. were sampled in the Colorado Front Range, CO. Classification tree models were built to predict probabilities of infestation. Regression trees and linear regression analysis were used to model amount of tree mortality in terms of basal area killed in infested stands. Classification trees had cross-validation estimates of classification accuracy ranging from 0.55 to 0.63. The data suggests that Douglas-fir beetle-attacked stands contain a high percentage of the basal area represented by Douglas-fir, high tree densities, and poor growth during the last 5 years prior to attack. Trees prone to attack by the Douglas-fir beetle within infested points also exhibited reduced growth rates. Tree and linear regression analysis indicate that initial amount of Douglas-fir basal area can be used as a predictor variable for the amount of basal area affected.