Forests With Insect Outbreaks Are Safer From Fires

Insect outbreaks and wildfires are two of the most destructive natural forest disturbances in North America.

Until now, it has been assumed that insect outbreaks feed wildfires by essentially turning trees into giant matchsticks.

Scientists have recently confirmed that insect outbreaks do affect wildfires, but not in the way we thought. The study, published in the journal Environmental Research Letters, suggests that insects can actually reduce wildfire severity.

Researchers conducted a census of the burn severity caused by large wildfires in Oregon and Washington State following recent outbreaks of two insects—mountain pine beetles, which target tree bark, and western spruce budworms, which attack leaves. Burn severity was assessed by measuring vegetation loss based on satellite images taken before and after each fire.

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81 fires over a 25-years span were analyzed, making this the largest study on forest fire severity following insect outbreaks ever undertaken.

Wildfires occurring after insect outbreaks were found to cause less severe damage than wildfires in forests that hadn’t experienced outbreaks.

“Our findings clearly show that insect outbreaks can reduce burn severity. So there is a connection, but just not the way most people thought," Garrett Meigs, a researcher at the University of Vermont and lead author of the study, said in a press release.

The authors suggest that severe insect outbreaks effectively thin out the forest, reducing the fuel available for blazes to spread.

"There is huge concern that insect outbreaks and forest fires will continue to increase with climate change," said Bill Keeton from the University of Vermont, a study co-author. "These threats remain significant, but our study suggests that major insect outbreaks, contrary to current thinking, can dampen future fire impacts.”

Knowledge generated from this research could help forest managers prioritize restoration efforts aimed at reducing forest fire risks, Keaton added. For example, the 2014 US Farm Bill included fuel reduction provisions for forests with insects and diseases. Based on the study’s findings, forest managers could factor in the natural forest thinning effects of insects into these efforts.

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