Hennigar C FEMC2007

Spruce Budworm Effects on Optimum Timber Supply and Carbon Sequestered for an Industrial Forest in New Brunswick

Chris R. Hennigar, Faculty of Forestry and Environmental Management, University of New Brunswick, P.O. Box 44555, Fredericton, NB, E3B 5A3, Canada, chris.hennigar@gmail.com
David MacLean, Faculty of Forestry and Environmental Management, P.O. Box 44555, 28 Dineen Drive, University of New Brunswick, Fredericton, NB, E3B 6C2, Canada, macleand@unb.ca

Spruce budworm (Choristoneura fumiferana Clem. (SBW)) severely defoliates balsam fir (Abies balsamea (L.) Mill.) and spruce (Picea spp.) in large periodic outbreaks. Major insect outbreaks kill trees over large areas, preventing the living biomass from continuing to accumulate and store carbon, resulting in carbon transfer to the atmosphere as dead trees decompose. The STAnd MANagement growth and yield model (New Brunswick Dept. Nat. Res.) was used to forecast stand volume growth loss and increased mortality following SBW defoliation in stands containing >10% balsam fir and spruce. STAMAN has been calibrated for relationships between SBW defoliation and resulting growth loss and mortality. We developed a modeling framework to integrate stand-level SBW timber volume impacts, projected from STAMAN, and carbon dynamics, derived from the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3), into a forest estate timber supply optimization model (Woodstock) for the 209,000 ha Black Brook District, in northwestern New Brunswick, Canada. Advantages of this integrated approach include using linear optimization to simultaneously re-optimize the harvest schedule, optimize salvage, and identify optimal areas for insecticide application to reduce losses of timber to budworm and/or maintain carbon in living biomass. The 2002 Black Brook District timber supply model and GIS data were used as the base scenario with no SBW outbreak. Scenarios exploring moderate and severe SBW outbreaks beginning in 2002, and optimum combinations of foliage protection (efficacy, frequency and spatial extent of application) and harvest strategies to reduce timber and carbon impacts were simulated.

Following simulated severe defoliation from 2007-2016, maximum harvest reductions of 35% were predicted for a moderate outbreak, for the 2012-16 period, and 46% for a severe outbreak, for the 2017-21 period. These impacts were reduced to 25 and 34% using re-optimized harvest scheduling and salvage. For area containing fir and spruce, C in live biomass and merchantable timber inventories were reduced 18% (870,000 tons of C) and 26% (3.3 million m3) for the 2007-2016 period for a simulated moderate outbreak and 20 and 30% for a severe outbreak scenario. Dead organic matter pools were relatively unaffected (<1%) by SBW outbreaks. Capturing salvageable volume was the main factor that reduced defoliation impact on harvest between base and defoliated (alternative, salvage) harvest scenarios. Spatial optimization of protected areas gave similar results to those obtained using protection priority assignments based on marginal stand-level volume reduction calculated by the Spruce Budworm Decision Support System. However, spatial optimization reduced the required area to be protected, for an equivalent harvest level, from 20% of the landbase to 17%, from 40% to 33%, from 70% to 53%, and from 100% to 66±4%. Combined optimized salvage and harvest re-scheduling could reduce future harvest losses by up to 30%. Incorporating tools such as optimized planning for salvage, alternative harvest scheduling and spatial allocation of foliage protection may reduce volume and carbon lost to SBW and also minimize the area of insecticide application. Differences between SBW timber and carbon impacts and optimum management strategies will be discussed.