Effects of spruce budworm outbreaks on balsam fir regeneration in mixed balsam fir-hardwood stands

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University of New Brunswick


Spruce budworm (Choristoneura fumiferana Clem.) defoliation on balsam fir (Abies balsamea (L.) Mill.) regeneration was studied in softwood, mixedwood, and hardwood stands in the early (3 years of defoliation) and late (7 years of defoliation) stages of an outbreak. Objectives were to determine 1) effects of stand type on spruce budworm defoliation on balsam fir regeneration of different heights, and 2) effects of defoliation, canopy openness, and competition of ground vegetation on regeneration height increment. Results indicated that high hardwood content reduced defoliation by 85% and mortality of balsam fir regeneration by 7% during the outbreak (especially in the late stage of the outbreak) and regeneration >30 cm had 10-15% more defoliation than short regeneration. Severe defoliation (100% to 200%) decreased height increment of balsam fir regeneration (especially tall regeneration) by 30-41% and canopy openness released regeneration with light defoliation during the outbreak. Competition from ground vegetation did not significantly affect height increment.