Global Climate Change Impacts in the United States 2009 Report Legacy site

Insect populations have a substantial impact on Canada's forest. They are a dominating disturbance factor and during outbreaks they can cause tree mortality over vast areas of forest. If the predicted climate changes take effect, the damage patterns caused by insects may be drastically altered, especially for the many insects whose occurrence in time and space is severely limited by climatic factors. This possibility substantially increases the uncertainties associated with the long-term planning of pest control requirements, with hazard rating models, with depletion forecasts, and with projections for the sustainability of future timber supplies. Moreover, because insect damage affects the rates of various processes in nutrient and biogeochemical cycling, potential changes in damage patterns can affect ecosystem resilience. This paper presents a number of plausible scenarios that describe how some key processes in the boreal forest's insect defoliator outbreak systems may respond to climate change. The spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used as an illustrative case study throughout. The potential importance of phenological synchrony in the dynamical interactions between species is emphasised. It is argued that natural selection may be a particularly important process in the response of insects to climate change and that climate change may already be influencing some insect lifecycles. The importance of threshold effects, rare but extreme events, and transient dynamics is emphasised, and the inadequacy of 'equilibrium' models for forest:pest systems noted. We conclude by discussing approaches to developing forecasts of how one of the boreal forest's insect defoliator-based disturbance regimes, as a whole, might respond to climate change.