Silvicultural control of spruce budworm

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Each year, forest insects and diseases damages cause 30% reduction in Canadian forest fiber productivity (Caroll and Volney 2002).  During its last outbreak (1968-1987), spruce budworm caused 500 million m3 losses (mortality + growth reduction) in the province of Quebec (Coulombe et al. 2004). Partial cutting in coniferous stands has been recently promoted in Quebec commercial boreal forest to increase the social acceptability of forest practices, to generate high quality logs, to modified schedules of tree harvesting over time in the context of sustainable yield, and to manage wildlife habitat.  We hypothesize that partial cutting could also be used to increase host tree resistance to spruce budworm and hence could reduce the economical impact of that major forest pest on the Canadian economy, but that the impact of stand partial cutting varies over time and according to the level of harvesting densities, site quality and host tree species.  The scientific approach adopted in the current research proposal involves the determination of insect responses (larval growth, development, food utilization and behavior, adult behavior), host tree responses (foliage chemistry, foliage production, foliage removed by the insect, growth, vigor) and abiotic conditions modifications (soil and air temperature and humidity) according to the various variables tested (partial cutting density, site quality, host species).  Our scientific approach will not only permit to document the impact of partial cutting on host tree resistance across a range of several important variables, but also will allow us to document the underlying biological and physiological processes involved at the insect and host tree level. This will contribute to a better understanding of how coniferous stand can be manipulated through silvicultural practices to reduce the economical impact of spruce budworm on the Canadian economy. Also, this study will provide a better understanding of the tree-insect system of interactions and consequently could have major impact on the role of the plant in the population dynamics of spruce budworm.