Long-term spruce budworm impacts: effects of 50 years of stand development and modelling topkill and defects

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University of New Brunswick


Spruce budworm (SBW; Choristoneurafumiferana [Clem.]) often results in tree death, a reduction in growth, or gradual tree top dieback, known as topkill. This study used three decades of data to examine long-term effects of SBW defoliation on tree form and defect formation, and five decades of data to examine balsam fir (Abies balsamea (L.) Mill.) stand development associated with SBW in comparison to stands unaffected by SBW and precommercially thinned stands from the Green River Thinning Trial. Results from the topkill analysis indicated that topkill probability increases with defoliation severity, but it is ultimately superseded by death. Measurements on surviving trees 25-years post-outbreak suggested that topkill can also substantially impact tree form. Results from the stand development analysis indicated that both thinned and unthinned stands produce more volume at younger ages than those defoliated by SBW due to poor stand-level production after the SBW outbreak from understocking. Further, regeneration analysis supported the supposition that the SBW-fir forests of northwestern New Brunswick form a self-regulating cyclical successional system.