Comparing growth and mortality of a spruce budworm (Choristoneura fumiferana) inspired harvest versus a spruce budworm outbreak

Abstract

Many current forest management regimes stress emulation of natural disturbance events, e.g., spruce budworm (SBW; Choristoneura fumiferana (Clemens)) outbreaks in a balsam fir (Abies balsamea (L.) Mill.) dominated forest, as the preferred method for ensuring sustainability of forest ecosystems. This study compared a SBW-inspired harvest treatment in 25 plots in northern New Brunswick with an uncontrolled SBW outbreak in 30 plots in the Cape Breton Highlands, Nova Scotia. Stand-level measurements before, during, and after each disturbance indicated similar reduction of living stand volume (70% reduction in emulation harvest versus 83% in SBW outbreak), mortality patterns, and lengths of disturbance (4 years of >10% mortality by density of predisturbance stand). Differences for the harvest treatment included higher cumulative postdisturbance blowdown (43% versus 8% of postdisturbance stand density), conversion to hardwood-dominated stands immediately after the disturbance, and faster growth response (immediate release of all species in the harvest treatment versus decreased balsam fir and white spruce (Picea glauca [Moench] Voss) growth and increased white birch (Betula papyrifera Marshall) growth in the SBW outbreak). There were significant differences in stand dynamics following the two disturbances. Results suggest that instead of emulating SBW disturbances, forest managers should be inspired by the spatial and temporal characteristics of SBW-defoliated stands and use significant key features of them to design harvest plans that satisfy management goals.