Climate change could alter the distribution of mountain pine beetle outbreaks in western Canada

Climate change can markedly impact biology, population ecology, and spatial patterns of eruptive insects due to the direct influence of temperature on insect development and population success. The mountain pine beetle Dendroctonus ponderosae (Coleoptera: Curculionidae), is a landscape-altering insect that infests forests of North America. Abundant availability of host trees due to altered disturbance regimes has facilitated an unprecedented, landscape-wide outbreak of this pest in British Columbia and Alberta, Canada, during the past decade. A previous outbreak in the 1980s, in central British Columbia, collapsed due to host depletion and extreme cold weather events. Despite the importance of such extreme weather events and other temperature-related signals in modulating an outbreak, few landscape-level models have studied the associations of extreme cold events with outbreak occurrences. We studied the individual associations of several biologically-relevant cold temperature variables, and other temperature/degree-day terms, with outbreak occurrences in a spatial-temporal logistic regression model using data from the current outbreak. Timing, frequency, and duration of cold snaps had a severe negative association with occurrence of an outbreak in a given area. Large drops in temperature (>10°C) or extreme winter minimum temperatures reduced the outbreak probability. We then used the model to apply eight different climate change scenarios to the peak year of the current outbreak. Our scenarios involved combinations of increasing annual temperature and different variances about this trend. Our goal was to examine how spatial outbreak pattern would have changed in the face of changing thermal regime if the underlying outbreak behaviour remained consistent. We demonstrate that increases in mean temperature by 1°C to 4°C profoundly increased the risk of outbreaks with effects first being manifested at higher elevations and then at increasing latitudes. However, increasing the variance associated with a mean temperature increase did not change the overall trend in outbreak potential.