Bark beetles have killed millions of acres of trees in western North America in recent years. This is predicted to increase the extent and severity of wildfires. In addition, firefighters have observed unusual and erratic fire behaviors in bark-beetle affected forests. Despite these observations, we lack a clear understanding of how bark beetle outbreaks affect wildfires. Rocky Mountain Research Station scientists and collaborators explored how bark beetle attacks change the moisture and chemistry of several tree species and how these changes affect flammability. Findings can help improve fire behavior and risk models to better predict and manage wildfires and protect property and human life.
Current fire behavior prediction models generally assume a uniform fuel source, but bark beetle affected forests are often a mosaic of green (living), yellow (dying), and red (dead) trees. This project explored changes in fuel moisture, terpenes (an organic chemical produced by some tree species), and combustibility in Rocky Mountain conifers resulting from bark beetle attack across these different stages of infestation.
Lodgepole pine (Pinus contorta) trees are chemically altered after mountain pine beetle (Dendroctonus ponderosae) attacks. Trees dry out rapidly during the red stage and are more flammable than unaffected trees.
Beetle attacks increase the emission rates of several highly flammable terpenes.
The flammability of yellow and red trees is higher than green trees because they have (1) shorter times to ignition, (2) lower temperatures at ignition, and (3) higher heat yields.
Needles of Engelmann spruce (Picea engelmannii) during the yellow stage of a spruce beetle (Dendroctonus rufipennis) attack contain less moisture and are more flammable than unattacked trees.
Fire managers and firefighters should be aware of the possibility of increased potential for crown fire initiation in beetle-affected stands as well as the prospect for rapid changes in fire behavior as fires move in and out of beetle-affected areas.