Insect outbreaks affect a forest area equivalent to harvesting and wildfire together. However, forest managers face several sources of uncertainty when reacting to insect disturbance. Not only do outbreak patterns change in response to forest conditions and climate, but their impacts on the forest can result in multiple and unpredictable forest responses. Understanding outbreak behavior can be used to produce sustainable forest management efforts that help mitigate the impacts of future outbreaks. In order to design “forests resistant to outbreaks”, we require a better understanding of the reciprocal interactions between insects and the forest at multiple spatial and temporal scales. We will achieve this by synthesising knowledge on three major forest insect pests of North America: mountain pine beetle, spruce budworm and forest tent caterpillar.

Results/Conclusions

Studying the similarities in response and factors affecting the outbreaks of these three major but different pests (i.e. the last two are leaf defoliators of conifers and hardwoods while the first feeds on the phloem) will permit us to identify the common characteristics of forest resistance as well as forest development after outbreak.  Forest managers make short-term decisions based principally on perceived damage, but forest response to an outbreak occurs on the order of decadal scales. Over long time scales, cumulative outbreaks and forest management activities change forest conditions that will affect future outbreak dynamics. Therefore, sustainable forest management has to deal with long term solutions. Promoting forest diversity in structure and composition emerges as a common and multiscale tool, that could provide a key to managing for outbreak-resistant forests, or to mitigate the forest response over a long term time scale.