The impact of tree and stand characteristics on spruce beetle (Coleoptera: Scolytidae) induced mortality of white spruce in the Copper River Basin, Alaska

Abstract

I examined the relationships between individual and stand-level characteristics of white spruce, Picea glauca (Moench) Voss, and the incidence of spruce beetle, Dendroctonus rufipennis Kirby, induced mortality. The study region, in the Kennicott Valley of the Copper River Basin, Alaska, has contained an active spruce beetle epidemic since 1989. I investigated the relationship among the individual traits of host age, size (diameter at breast height, DBH), and growth rate (basal area increment, BAI) and mortality from the spruce beetle. I also examined the effects of stand density, mean DBH, and mean BAI on percent mortality within plots. Survival was higher for younger, smaller, and faster-growing trees. However, the effect of age is not significant when included in a logistic regression model examining the effect of individual host traits on host survival. Mortality increased with increasing DBH and decreasing BAI, and there was a significant interaction between DBH and BAI. While the proportion of individuals killed by the spruce beetle significantly differed between stands, I found no significant relationships between stand-level characteristics and mortality rate. This research suggests that the individual traits of host size and growth rate, as well as their interaction are the best predictors of susceptibility to spruce beetle-induced mortality in this system.