Modelling disturbance synergies: predicting Dendroctonus pseudotsugae outbreaks after widespread wildfires in dry conifer forests

Forest disturbance regimes around the world are undergoing a period of rapid change. In the dry interior forests of western North America, both wildfires and insects have historically interacted to create diverse and resilient landscapes, but there is increasing concern that alterations in one or more disturbance regimes due to a changing climate could create novel, and potentially harmful disturbance synergies, pushing these forests past key ecological tipping points. To investigate the potential impact of compounding disturbances in dry interior forests, we initiated a study to elucidate the relationship between Douglas-fir beetle (DFB; Dendroctonus pseudotsugae) and wildfires after a series of record-breaking wildfire seasons in British Columbia, Canada. DFB is one of the most significant agents of mortality in Douglas-fir (Pseudotsuga menziesii), a keystone conifer species with important cultural, ecological, and economic value. As climate change continues to affect these landscapes, there is concern that DFB outbreaks could increase in size and severity in the coming decades as wildfires become more frequent, and potentially more severe. Across three large burn complexes, we found the outbreak potential of DFB to be constrained by pre-fire stand characteristics, burn severity, and competitive pressure from other members of the subcortical woodboring insect guild (Coleoptera: Buprestidae, Cerambycidae) in the first year following fire. Results will be discussed within the context of future management strategies for changing disturbance regimes in a warming environment.