SEATTLE — Don’t blame bark beetles for catastrophic wildfires, such as the blaze that blackened more than 23,000 acres of Kittitas County, Wash., last summer, some scientists say.
In a paper published last week in Natural Areas Journal, scientists say they found through a literature review that bark beetles do not substantially increase the risk of crown fire in lodgepole pine and spruce forests, as commonly assumed.
Instead, they concluded, the fires are primarily caused by dry conditions exacerbated by climate change. And as long as severe droughts continue, so will wildfires, regardless of beetle populations, the scientists determined.
“What we need is a rational energy policy, because climate change is what is really driving these big changes,” said Dominick DellaSala, who co-authored the report.
The scientists set up a literature review to test the prevailing assumption that dying trees caused by bark-beetle infestation was coupled to the high incidence of fire in the western United States. The scientists also wanted to learn if forest thinning was a dampening or remedial measure before, during or after fire.
After combing through hundreds of scientific studies, the scientists confirmed that beetles were killing trees throughout the West — not a surprise. But they also found that the beetle-killed trees were not actually related to the forest fires, under most conditions. Instead, they found those fires are contingent on dry conditions. That, the scientists concluded, points the finger to a larger underlying cause of bigger forest fires: climate change.
“Mother Nature is not there to provide the checks and balances because the climate is warming. And when you get more drought, that combines with the effects of beetles to put added stress on trees,” DellaSala said.
However, more beetle-killed trees don’t necessarily stoke crown fires. In fact, depleted stands of beetle-killed trees might actually pose less, not more, risk of crown fire because of gaps as branches drop.
Of course, that could create more fuel on the forest floor, which could stoke ground fires, cautions Glenn Kohler, a forest entomologist with state Department of Natural Resources. “These things can cut both ways,” he said. Kohler cautioned that understanding of the causes and preventions of wildfire in the West is still evolving. “The jury is still out.”
But these authors found as long as severe droughts persist, so will the risk of wildfire — beetles or not.
But drought and high temperature are likely also the overriding factors behind the current bark-beetle epidemic in the western United States,” said Scott Hoffman Black, co-author of the paper, and executive director of the Xerces Society in Portland, Ore., a nonprofit dedicated to the preservation of invertebrates.
DNR surveys have found more acres of bug-infested forests in Washington than in the past 40 years, with about a third of the state’s forestland east of the Cascades at risk for die off and tree damage from bugs and disease.
In the short term, the best defense for homeowners living in wildfire country is to clear combustibles from the immediate vicinity of the home, Kohler of the DNR said.
“It’s all about fuel, whether it’s alive or dead, and if you reduce the amount of fuel, crown fires are less likely to happen.”
Once a big fire gets going, it won’t matter much whether the trees involved are dead or alive. “If you get a raging crown fire, it can burn green trees just as effectively.”
Homeowners also are encouraged to thin trees around their property to ward off beetles by reducing competition among the trees, Kohler said.
Black agreed small-scale thinning could help prevent beetle infestation and fire. But in a big infestation, thinning’s not the answer, he said. At that stage, the infestation appears to be unstoppable, Black said. “We don’t want to go across large landscapes doing these large thinning projects thinking that is going to solve the problem.
“We really can’t manage our way out of this.”
Large-scale logging operations to control beetle outbreaks could also have unintended short- and long-term consequences, Black said, including habitat fragmentation from road building in forested areas and siltation of streams.