Influence of mountain pine beetle outbreaks on large fires in British Columbia

Abstract

A key uncertainty in understanding climate change effects on wildfires in western North America is the role of mountain pine beetle (MPB) outbreaks in driving wildfire occurrence and severity. In this study, we investigated the complex relationship between MPB outbreaks, other environmental factors, and wildfire occurrence in British Columbia (BC), Canada. We adopted a fire risk analysis method developed for fire occurrence prediction to separate the effect of changing fuel conditions on wildfires in BC when neither post‐outbreak fuel conditions, climate, nor management is stationary. Using lasso‐logistic regression and a novel variable ranking procedure, we determined that MPB‐affected areas had 1.7 times more large lightning‐caused fires (≥100 ha), as the likelihood of large lightning‐caused fires increased by 40% in these areas and likely contributed to the increased burned areas in BC. Meanwhile, the likelihood of large human‐caused fires decreased in MPB‐affected areas. Fire weather factors were most influential for both lightning‐ and human‐caused fires, while anthropogenic factors were most influential for human‐caused fires. Fuel dynamics following MPB outbreaks vary across the wide distribution of a host species such as lodgepole pine, at stand and landscape levels. Furthermore, the expression of the effects of MPB and other disturbances on wildfire is also conditional on, as well as confounded with, many other environmental factors and management activities that vary across western North America. Therefore, a lack of consensus on the impacts of MPB on wildfire is not surprising.