Optimized harvest planning under alternative foliage-protection scenarios to reduce volume losses to spruce budworm

Abstract

Spruce budworm ( Choristoneura fumiferana Clem.) severely defoliates balsam fir ( Abies balsamea (L.) Mill.) and spruce ( Picea spp.) in large periodic outbreaks and represents one of Canada’s most damaging and widespread forest insects. We present a modeling framework that integrates stand-level spruce budworm volume impacts used in the Spruce Budworm Decision Support System (SBWDSS) into an industrial-scale timber supply model for the 209 000 ha Black Brook District in northwestern New Brunswick, Canada. This approach uses linear optimization of harvest scheduling, salvage, and insecticide application to minimize volume reduction. One hundred and ninety-five scenarios were simulated, including normal and severe spruce budworm outbreaks, beginning in 2002, with combinations of varying insecticide efficacy, timing, and spatial extent of protection. After simulated severe defoliation from 2007 to 2016, maximum harvest reductions of 35% were predicted for a normal outbreak for the 2012–2016 period, and 46% for a severe outbreak for the 2017–2021 period; these impacts were reduced to 25% and 34% using re-optimized harvest scheduling and salvage. Results suggest that combined optimized salvage and harvest rescheduling could reduce future harvest reductions by up to 12%. Spatial optimization of protected areas gave similar results to those obtained using protection priority assignments based on marginal stand-level volume reduction in the SBWDSS.

Re-examining wood supply in light of future spruce budworm outbreaks: A case study in New Brunswick

“…Two outbreak patterns, termed "moderate" and "severe", were presented in previous studies (Erdle and MacLean 1999, MacLean et al 2001, Hennigar et al 2007; Fig. 2b-c).…”

“…Methods used to project SBW impacts using the STA-MAN stand growth model were similar to those used by MacLean et al (2001) and Hennigar et al (2007), with three improvements: 1) ability to project salvageable volume from SBW-caused mortality, 2) modeled ingrowth from regenerating tree cohorts (calibrated from Erdle and Ward [2008] improvements to STAMAN), and 3) explicit separation of relative defoliation differences expected between fir and each spruce species (Hennigar et al 2008).…”

“…minimize the maximum defoliation-caused harvest reduction from current levels-in other words to make the harvest level reduction as small as possible in the time period at which it is greatest-following iterative re-optimization techniques described by Hennigar et al (2007). This included adding a term to penalize the objective value by -1 per ha treated (discounted at 8% over time as well), to ensure that scheduled harvest, salvage, and protection treatments would only occur if they resulted in objective function improvements.…”

“…Forest protection (spraying of biological insecticide), salvage harvesting, and strategic re-planning have all been shown to mitigate the wood supply impacts of defoliation by SBW (Hennigar et al 2007). However, such measures are expensive and difficult to implement, and decisions about if and to what extent they should be applied hinge largely on the magnitude of likely benefits and associated costs.…”

“…To help define the former, we conducted analyses to quantify the effects of various mitigation strategies that combine 1) foliage protection (timing and extent), 2) salvage harvest, and 3) replanning of scheduled harvest and silviculture treatments. We employ the Hennigar et al (2007) integrated SBW planning approach 3 to examine effects of these strategies on all Crown forest in New Brunswick, under scenarios of an impending SBW outbreak.…”