Spruce budworm and forest dynamics in a boreal mixedwood stand

We describe and summarize a study of the population ecology of a spruce budworm (Choristoneura fumiferana Clemens) outbreak in a boreal mixedwood stand near Black Sturgeon Lake, Ontario. The purpose of the study is to estimate rates of change in the abundance of spruce budworm throughout the outbreak and to relate these changes in abundance to ecological processes. After than 10 years of defoliation, there is significant yet differential mortality among susceptible trees. Losses have been greatest among codominant balsam fir (Abies balsamea [L.] Mill.), intermediate for white spruce (Picea glauca [Moench] Voss), and lowest for black spruce (Picea mariana [Mill.] B.S.P.). Nonsusceptible species such as trembling aspen (Populus tremuloides Michx.) now dominate the canopy. As gaps have opened in the stand, a diverse herbaceous layer has developed, as well as advance regeneration of balsam fir. Influence of mixedwood structure on budworm dynamics and of budworm on mixedwood dynamics is discussed.