Predicting Impacts on Balsam Fir due to Hemlock Looper and Balsam Fir Sawfly Defoliation for a Decision Support System

Some of Canada's major insect pests periodically attack balsam fir (Abies balsamea (L.) Mill.) with results that are economically catastrophic. It is a preferred host for severely damaging defoliators like spruce budworm (Choristoneura fumiferana Clem.), balsam fir sawfly (Neodiprion abietis Harris) and hemlock looper ( Lambdina fiscellaria fiscellaria Guen.). Though much is known about spruce budworm defoliation and its related impacts, very little information existed about the remaining two species which differ in their feeding behavior. This dissertation quantifies and compares defoliation and impacts on host trees at the tree, stand and forest level due to the three insects. The quantified information was used to build and implement decision support system (DSS), allowing discussion of key policy alternatives for reducing impacts on Forest Management District 15, Newfoundland.;Firstly, cumulative defoliation due to balsam fir sawfly and hemlock looper was estimated from defoliation per age class of foliage and compared to aerial defoliation surveys. Knowing the importance of defoliation prediction in pest management, a Bayesian Network model was proposed that improved and automated defoliation prediction for balsam fir sawfly. Key component of DSS, i.e., empirical relationships between defoliation and impacts (growth and mortality) were quantified from permanent sample plot data and dendrochronology. Following the existing spruce budworm DSS framework, STAMAN stand growth model was used to grow stands with and without defoliation thus calculating % stand volume losses and timber volume loss across a forest landbase.;It was estimated that defoliation caused by balsam fir sawfly from 1996-2008 has caused maximum total operable softwood growing stock and softwood harvest volume reductions of 26% and 31%, respectively. In contrast, defoliation caused by hemlock looper in the same period caused a maximum 3% reduction in softwood harvest levels. Hemlock looper was found to produce maximum impacts followed by balsam fir sawfly and spruce budworm. Due to long-term legacy effects on stand yields and delayed recovery, harvest volume reductions may occur for up to 50 years after outbreak collapse. Re-optimization of harvest schedules can be used to calculate new even-flow long term harvest levels and reduce impacts at the forest scale. Best management option for reducing damage depends on type, severity and extent of insect damage, but consists of a combination of thoughtful, well planned biological insecticide protection as well as forest management approach through harvest level reductions, harvest rescheduling and salvage.