Forecasting the response of spruce budworm defoliation to climate change in Ontario

Abstract

Predicting the effect of climate change on insect populations is critical to improve the reliability of forest management plans, wood supply projections, and pest protection programs. In this study, we use an empirical model to relate the spatial distribution of past defoliation by spruce budworm ( Choristoneura fumiferana Clem.) in Ontario to bioclimatic variables. We then apply data from six climate change scenarios to this model to project potential changes in the distribution of defoliation for 2011–2040. The spatial distribution of historical defoliation was found to be related to winter maximum and minimum temperatures, forest content in balsam fir ( Abies balsamea (L.) Mill.) and white spruce ( Picea glauca (Moench) Voss), and spring and summer minimum temperatures. All six climate change scenarios project broadly similar changes in the spatial patterns of defoliation: (i) an extension of the northern limit of defoliation as far as available data go or close to it, (ii) a decrease in the frequency of defoliation in the center of the historical defoliation belt, and (iii) a persistence of the southern limit of defoliation. This leads to a projected increase of the total area defoliated of between 22.8% and 25.5%, while the mean frequency of defoliation, calculated over the whole study area, would slightly increase (+1%) or decrease (–17.7% to –2.9%).