Interaction between forest tent caterpillar and forest composition: Role of predation in outbreak dynamics and effects on litter, soils and tree regeneration

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The forest tent caterpillar (FTC) is a significant defoliator of hardwood stands throughout Canada. Currently, in Quebec there are two foci in which outbreaks appear to cycle independently: one in the south on sugar maple and one in the north on trembling aspen. In these forest types, severe outbreaks occur at approximately 10-year intervals and are responsible for decreases in forest productivity. Historically, outbreaking populations collapsed after one or two years of defoliation, but longer and more severe outbreaks have been observed in the recent years. For this reason, in the context of the projected climate change it is thought that FTC outbreaks may become more severe and result in more significant losses of forest productivity. FTC outbreaks are characterized by extreme population fluctuations and highly variable mortality rates. Recent studies suggest that predation plays an important role in population control. However, our understanding of predation rates and the relative importance of different predators on FTC remain highly hypothetical. Furthermore, during outbreaks FTC could increase the amount of organic matter to the soil and increase resources available to detritivores. These modification could have important effects on the structure of soil invertebrate communities and influence decomposition of organic matter, nutrient availability, and tree seedlings survival and growth. On the long term, these effects could exert important controls on forest stand composition. The objectives of this project are to better understand 1) the role of predators in keeping down and ending FTC outbreaks and 2) the effects of FTC outbreaks on soil arthropod communities, soil processes, and tree regeneration. This project will provide a better understanding of forest ecosystem functioning and contribute to the development of innovative silvicultural approaches. For instance, our project will allow for the identification of stand types most likely to be affected by future FTC outbreaks. This study will also contribute to better anticipate future FTC outbreaks and conduct pre-emptive harvesting of vulnerable tree species and stand types. These interventions will help maintain the timber supply for the Canadian forest industry.**********