WWETAC Projects

Project Title: Synthesis of effects of insect-caused tree mortality on fire characteristics

Principal Investigators: Jeffrey Hicke, University of Idaho/Western Wildland Environmental Threat Assessment Center, USDA Forest Service; Jane Hayes, Pacific Northwest (PNW) Research Station, USDA Forest Service (FS); Morris Johnson, PNW Research Station


Key Issues/Problems Addressed:

The killing of millions of trees by bark beetles in western North America have raised concerns about subsequent wildfire, but studies have reported a range of conclusions, often seemingly contradictory, about effects on fuels and wildfire.

Setting and Approach:

This review evaluated 39 recent studies on the effects of insect-caused tree mortality on fire characteristics.  Study findings were analyzed for scientific methods used, consistencies, knowledge gaps, and methodology challenges.

Key Findings:

  • The reviewed studies suggest that bark beetle outbreaks can affect fuels and fire behavior.  The types of changes depend on the time since outbreak, and fuel and fire characteristics, suggesting that generalizations about the effects of bark beetle-caused tree mortality on fire characteristics are unwarranted.
  • While many studies reported that bark beetle activity was not as important as other factors driving fire behavior, severity and extent, the impact of beetle-killed trees can be significant when compared to forests not attacked by beetles.


Bark beetles are found to influence fuel and fire behavior and their effects differ depending on time since outbreak and other factors.  This review provided a conceptual framework based on published studies and identified that significant agreement exists in some situations, and that substantial gaps in knowledge also exist. Large variability in forest structure, mortality rate, and environmental conditions within areas attacked by bark beetles suggests challenges in characterizing general responses of fuels and fire characteristics applicable across affected forests.


Hicke, J.A., M.C. Johnson, J.L. Hayes, and J.K. Preisler. 2012. Effects of bark beetle-caused tree mortality on wildfire. Forest Ecology and Management 271:81-90. (PDF, 369 KB)