Are Bark Beetles To Blame For Increased Western Wildfires? Study Says Not Likely

Mar 24, 2015

Take a drive or a walk through many of Colorado's mountains, and you'll see a whole lot of dead trees. Mostly lodgepole pine killed by mountain pine beetle, the gray trees look like prime kindling, some standing, many fallen like so many pickup sticks across the landscape. The mountain pine beetle has killed 46 million acres of the West's forests, leaving a scar no forest visitor can miss.

Conventional wisdom has long held that these beetle-killed forests are more likely to burn. They certainly look that way. But scientists have been questioning the idea that such forests burn more for a few years. A 2013 study from Colorado State University pointed the finger at drought, not bark beetles, for increased wildfire. Now a new, more comprehensive study from a team of scientists at the University of Colorado Boulder has found that forests with widespread beetle kill are not more likely to burn.

Sarah Hart, a postdoctoral researcher at CU who led the study, said the scientists looked at a range of Western wildfires across multiple years.

"We found that forests infested by mountain pine beetles are not more likely to burn at a regional scale. So while the area infested by mountain pine beetle has dramatically increased over the past 15 years, the annual area burned hasn’t increased with this increase in beetle kill," Hart said in a statement.

This matters because the belief that beetle-killed forests are more likely to burn affects how taxpayer money on forest management is spent.

In 2014, Congress allocated $200 million in the Farm Bill to reduce the risk of insect outbreaks, disease and wildfire in beetle-killed forests. If beetle-killed forests are not more likely to burn (and may even be a good thing for forests, helping them adapt to climate change), it calls into question why a lot of money and effort is being spent to fight the beetles and thin the forests.

It is true that wildfires have been more widespread and severe in recent years, as has bark beetle kill. But when the researchers tried to find a correlation between wildfires and beetle killed areas, they did not find one.

The scientists suggest instead that increasingly severe wildfires are caused by a problem that Congress has yet to do much about: climate change.

The research was published March 23 in the Proceedings of the National Academy of Sciences.