Don't blame bark beetles for fire risk

A new study suggests hot dry weather, not beetles, make forests go up in smoke.


Years ago, some good friends of mine bought a house outside of Fort Collins, Colorado. An army of dry, red-needled trees – casualties of a massive mountain pine beetle infestation – surrounded their property. To me, the landscape looked ripe for a wildfire.

And it was: In June 2012, that forest and mountainside neighborhood ignited in the High Park fire. But the infestation wasn’t to blame for the blaze, one among many in what became a historically severe fire season. “I think it’s safe to say that there is no effect of mountain pine beetle on the area that’s burning,” says Sarah Hart, a forest ecologist at the University of Colorado, Boulder. “We’re having lots of fire across the West; it’s because it’s warm and dry.”

Hart coauthored a study published this week in the Proceedings of the National Academy of Sciences showing no relationship between the amount of forest killed by bark beetles and the number of acres burned in recent severe wildfires.

The conclusion is a departure from the conventional media and political narratives that have espoused the beetle-fire connection, even as scientists and forest managers debate the idea and gradually uncover a much more nuanced picture. And it’s important, because those narratives are often used to justify logging beetle-killed forests.

Living in Colorado during the 2012 fire-season and reading headlines like “High Park Fire Follows in Pine Beetles’ Tracks” helped inspire Hart and her colleagues to test the link in the first place. They knew there wasn’t much scientific evidence supporting it.

Other studies on fire risk and pine beetles have been based on computer models or looked at just one or two fires, so this time the scientists looked at the whole West, comparing Forest Service maps of mountain pine beetle infestations to burned areas. They found that even though the total area infested by mountain pine beetle increased between the years 2000 and 2013, the amount of land that burned did not.

During the peak fire years of 2006, 2007, and 2012, only five percent of the forest area burned across the western United States had recent bark beetle infestations. The researchers suspect that beetles don’t change the odds of burning because when it's extremely hot and dry, forests get so parched they will support serious conflagrations with or without beetle kill. 

Fire researchers still have questions about how beetles affect other aspects of fire behavior that are especially important to firefighters – like how hot fires burn, how fast they spread, and how predictable they are. The recent study also doesn’t negate the safety benefits of clearing dead trees – which are prone to topple – from around homes, trails or power lines.

Hart and her colleagues hope their paper will inform discussion about the underlying reasons for fire risk and inspire more effective policies for coping with it. Right now, conventional wisdom is still driving some restoration efforts. The 2014 Farm Bill authorized $200 million in taxpayer funds for projects, including forest thinning, meant to address the risk of insect outbreaks and wildfire on national forests. “Large landscapes of dead and infested trees pose a significant threat of forest fires, as evidenced by last summer’s historic Colorado, California, and Idaho wildfires,” reads a letter of support signed by at least seven Senators.

“For any manager concerned about whether their forests are going to burn or not,” says Hart, “I think they should focus more on trying to adapt to changes in climate rather than changes to fuels from mountain pine beetle infestation.”

And if she could go back and rewrite those 2012 fire headlines today, she says, she would go for the much less dramatic, but far more accurate, “Warm and Dry Weather Promotes Widespread Fire.”

Sarah Jane Keller is a High Country News contributor based in Bozeman, Montana. She tweets @sjanekeller.

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