Canada’s boreal and mixed-wood forests are dynamic ecosystems shaped by multiple disturbances, including wildfires, insect outbreaks, and forest harvesting. These disturbances interact in complex ways, altering forest fuels and vegetation composition, which directly affect ecosystem structure and function.

Outbreaking insects such as the eastern spruce budworm (SBW; Choristoneura fumiferana), jackpine budworm (JPBW; Choristoneura pinus), and the mountain pine beetle (MPB; Dendroctonus ponderosae) can significantly modify forest fuels, ultimately influencing fire activity, including fire occurrence, behaviour, and outcomes (i.e., burn severity). While it is generally accepted that forest insects impact fire activity, the precise mechanisms of this influence and its variability over space and time remain uncertain.

The anticipated northward expansion of multiple species of forest insect pests, combined with projected climate-related increases in forest fire activity in the boreal forest, introduces significant uncertainty regarding future disturbance interactions. This uncertainty extends to their effects on forest composition and connectivity, ecosystem services, and well as human health and safety.

In this research theme, we aim to gain a deeper understanding of the spatial and temporal dynamics of these critical disturbance interactions, and their implications for managing Canada's boreal and mixed-wood forests. Using multiple approaches that combine field observations, remote sensing (e.g., LiDAR), statistical analysis, machine learning, and simulation modelling, we are investigating how changing fuel complexes are affecting fire behaviour, severity, and landscape resilience.

Recent work in this theme identified an important relationship between fire ignition probability and historical SBW defoliation. Specifically, we found that SBW outbreaks generally increase the risk of ignition 8-10 years after defoliation but decreases this risk immediately following defoliation (within1 year). Building on these findings, we are currently investigating the impact of SBW and JPBW outbreaks on fire suppression, area burned, and fire severity, as well as the underlying mechanisms driving these interactions between forest structure and wildfire. A particular focus of this work is using terrestrial LiDAR to quantify fuel structure and better understand the outbreaks’ impacts to fire behaviour.

The long-term goal of our research in this theme is to develop evidence-based tools and recommendations for managers to proactively address the impacts of insect outbreaks, changing fire regimes, and their interactions. A better understanding of these disturbance linkages is crucial for maintaining ecosystem function and resilience of Canada's boreal and mixed-wood forests in the face of a rapidly changing climate.