COS 148-4 - Multivariate analysis reveals that mountain pine beetle outbreaks significantly influenced the occurrence of large fires in British Columbia

Abstract: Forest disturbances change the stand structure as well as the regimes of other disturbances. Identifying the connection between the two major forest disturbances in western North America–Mountain pine beetle (MPB) infestation and wildfires–is critical to determine future disturbance regimes in conjunction with projected climate changes. The influence of MPB infestation on wildfires, however, has been obscure under the presence of confounding environmental factors such as weather, vegetation, geographic and anthropogenic characteristics. Based on the massive outbreak of MPB infestation in the early 2000s and the surge of wildfires in the late 2010’s in British Columbia (BC), Canada, we investigated the landscape-level influence of MPB infestation on fire occurrence and size in addition to a number of potentially confounding covariates. We analyzed how the MPB infestation and its severity have a significant influence on subsequent fire occurrence and large fire probability using spatio-temporal grid cells with the disturbance history over BC. Lasso-logistic regression with balanced response-based samples of the grid cells was adopted. Based on the variable ranking and selection algorithm, we found out that the relative risk of large lightning-caused fires over 100 ha was 19 % higher in the MPB-affected area, and 40 % greater as the MPB-induced tree mortality increases by 1 standard deviation. We presumably concluded that the significant influence of MPB on fire characteristics in BC contrary to the prior studies was due to 1) the wide and contiguous forest stands of MPB host species in BC, 2) inclusion of daily fire weather and other environmental confounding factors that are related to managemental activities, and 3) the separate analysis of MPB impact on wildfire characteristics by fire cause. The results of this study contribute to expanding the framework of the synergic impact between the two disturbances at a landscape level, and support the decision makers’ priorities for deploying fire management resources after the MPB infestation.