Ten-year tree mortality following a jack pine budworm outbreak in Saskatchewan

The face of jack pine (Pinus banksiana Lamb.) trees growing in a variety of stand conditions was assessed annually for a decade following an outbreak of jack pine budworm (Choristoneura pinus Freeman) in central Saskatchewan. Mortality was clearly associated with the severity and damage sustained by the trees during the second year of the defoliation episode. The pattern o f mortality was remarkably similar among stands that originated in decades that spanned 60 years. Mortality rates were highest in stands that originat ed in the 1890s and were lowest in stands of the most recent origin (1940s) . Defoliation severity, the length of dead top, diameter at breast height, and relative tree height expressed as a standard normal variable accounted for 94% of the variability in survival time. A nonparametric proportional h azards model was developed to evaluate the relative risk of individual tree s dying. Defoliation is an important process in determining stand density, basal area, and volume after juvenile stand development is complete. The re sults presented suggest a novel method to determine the hazard of trees in stands and thus assess the vulnerability of stands to future budworm attack .