TREE MORTALITY RISK OF OAK DUE TO GYPSY-MOTH

We present prediction models for estimating tree mortality resulting f rom gypsy moth, Lymantria dispar, defoliation in mixed oak, Quercus sp ., forests. These models differ from previous work by including defoli ation as a factor in the analysis. Defoliation intensity, initial tree crown condition (crown vigour), crown position, and species grouping classes were highly significant in categorical analysis of variance fo r mortality. Heavy defoliation Intensity was shown to have a strong, c onsistent influence in increasing the probability of tree mortality. C lassification and Regression Tree (CART) analysis, a binomial decision tree procedure, was used to develop prediction models of mortality ri sk for use by forest managers. The best decision tree had 65 groups th at correctly classified 75% of the live trees and 76% of ihe dead tree s. Models were run separately by defoliation class and provided correc t classifications between 63 and 78% of the trees. Forest land manager s can use these models to assign probabilities of death for moderate a nd heavy defoliation intensity levels and compare predicted mortality to mortality of undefoliated trees to determine how gypsy moth defolia tion will affect their stands. The probabilities can be used to develo p marking guides based on projected defoliation levels for implementin g silvicultural treatments to minimize gypsy moth effects in forest st ands prior to infestation.