The relationship between climate and outbreak characteristics of the spruce budworm in eastern Canada

The relationship between outbreak characteristics of the spruce budworm and the combination of climate, forest composition, and spatial location was examined in eastern Canada by the method of constrained ordination. Approximately 54% of the spatial variability in outbreak pattern, as described by a matrix of four outbreak characteristics, was explained by the spatial pattern of the climate (a matrix of six variables), forest composition (a matrix of seven variables), and spatial location (a matrix of two variables). The relationships between outbreak variables and climate variables were highlighted, and future outbreak characteristics of the spruce budworm were projected using simulations of a global circulation model for the period 2081–2100 where CO₂ concentrations reach a maximum of approximately 550 ppm. Future outbreaks are predicted to be an average of approximately 6 years longer with an average of 15% greater defoliation. The methodology is described and the potential effects of climate change on landscape-scale outbreaks of the insect are discussed.