Factors affecting trembling aspen ( Populus tremuloides Michx.) health in the boreal forest of Alberta, Saskatchewan, and Manitoba, Canada

Abstract

The value of trembling aspen ( Populus tremuloides Michx.) as a resource has increased in Canada in recent years, but key information regarding the health of this species and its interrelationships with biotic and abiotic agents is lacking. A regional study was conducted to (i) assess the general health of trembling aspen trees in the three prairie provinces of Canada, (ii) determine the incidence of biotic and abiotic agents affecting these trees and (iii) determine what factors most influenced the health of trembling aspen trees between forest tent caterpillar ( Malacosoma disstria Hübner) outbreaks. A total of 8296 trembling aspen trees in 85 plots were monitored during 1992–1994. Trembling aspen health was assessed and related to biotic and abiotic damage agents and symptoms. Trembling aspen in the study area were generally healthy: crowns were in good condition, trees had few pests, and mortality rates were low. Confidence intervals for proportion of trees dead less than 2 years are reported by age class. Large aspen tortrix ( Choristoneura conflictana [Wlk.]) and poplar peniophora ( Peniophora polygonia [Pers.:Fr.]) Boud. were the most common pests, occurring on 15 and 13% of live trees, respectively; incidences of other pests were <7%. Significant associations between incidences of pests and several stand characteristics were found. Regression analysis showed tree age, a climate moisture index, number of years of forest tent caterpillar defoliation, and incidence of Armillaria root disease ( Armillaria spp.) accounted for a significant proportion of the variation in trembling aspen health and mortality. Our results highlight the need to consider pests, especially forest tent caterpillar and Armillaria root disease, in the management of trembling aspen or in landscape-level simulations of trembling aspen productivity.