Effects of Mixed Stand Management to Reduce Impacts of Spruce Budworm Defoliation on Balsam Fir Stand-Level Growth and Yield

Abstract

Abstract Mixed hardwood-balsam fir stand management has been proposed as one silvicultural technique to reduce spruce budworm damage to balsam fir. An analysis was conducted using published results from New Brunswick, Canada, and northern New England, USA, to assess whether optimum hardwood levels (percent volume) could be determined for various levels of budworm defoliation. The goal was to maximize standing balsam fir volume and to determine trade-offs between reduced damage (hence reduced volumes losses) versus the amount of fir volume lost as a result of allocating growing space to hardwood species. Optimum hardwood levels depended on severity of budworm attack. Below 45% defoliation (5 yr average), the amount of balsam fir volume lost to increased hardwood growing space exceeded the amount of volume protected. As defoliation severity increased above 45%, the optimal hardwood levels increased. At severe levels of defoliation (> 75%) optimal hardwood content was approximately 50% of initial standing volume. The results suggest that mixed stand management can potentially reduce balsam fir volume losses in areas with frequent severe spruce budworm outbreaks. North. J. Appl. For. 16(1):19-24.