Wildfire containment probability is not affected by eastern spruce budworm defoliation in Ontario, Canada

Background Stand-replacing wildfires and eastern spruce budworm outbreaks (Choristoneura fumiferana; SBW) are important disturbances in the boreal forest. SBW defoliation can affect fire behaviour by altering fuel loads and connectivity, thereby promoting the transition of low-activity surface fires into crown fires. However, little is known about how these altered fuels impact the effectiveness of fire suppression. Aims To assess key drivers of initial attack (IA) success in Ontario’s boreal forest and determine if incorporating SBW defoliation data improves predictive models. Methods We developed random forest models of fire containment using established predictors including fire weather, fire size at IA and region. We then evaluated if the inclusion of time since SBW defoliation improved model performance. Key results Fire size at IA was the most influential variable for determining whether a fire escaped containment. Contrary to our hypothesis, we did not find evidence that SBW defoliation greatly improved model performance. Conclusions and implications The size of the fire at IA was the most important variable in determining successful containment. Although budworm defoliation has been shown to affect other aspects of fire hazard, we were unable to identify an influence on IA success. Future work could benefit from focused investigation into how historical SBW defoliation affects fire behaviour.