CHELAN COUNTY, Wash — As climate change worsens, forest health is taking a hit in the form of insects, leading to increased wildfire danger.
Glenn Kohler, forest entomologist for the Washington Department of Natural Resources (DNR), said there are about a dozen bark beetle species that are considered pests. In the last decade, Kohler said DNR has seen a trend where changing environmental factors are creating a situation where these pests thrive, increasing their negative impact.
“Over the last 10 years we’ve noticed with some of these bark beetles, the western pine beetle in the Ponderosa and the fern graver in the grand fern primarily, those are two great examples of bark beetles that really enjoy and are successful at killing drought-stressed trees," Kohler said. "We've been going through a period of hotter and more intense droughts the last 10 years.”
When the beetles kill trees, those dead trees then fill forests, eventually falling and blanketing forest floors, creating a situation where wildfires spread faster due to all the dry fuels.
He said each type of beetle preys on a different kind of tree. For example, the mountain pine beetles attack dense trees that are growing too close together and ultimately threaten each other, giving an environment for mountain pine beetles to take advantage of already stressed trees. Douglas-fir beetles attack trees that are already dead, and western pine beetles attack drought-stressed trees.
Kohler said it can take hundreds and even thousands of beetles to kill one single tree. He said the adult beetles enter the tree and lay their eggs, then the larvae exit the tree by mining their way out, which is ultimately what kills the tree.
The problem is that environmental factors recently have given the beetles a space to thrive, so DNR is seeing an increase in dead trees.
“These tree species are all adapted to deal with that summer drought. But what’s happening is the shoulder seasons of that drought are getting wider and we’re getting higher temperatures so those days over 90 degrees, we’re getting more of those,” he said. “But the problem is we’ve been having those regularly and longer periods so we get this cumulative effect and whatever defense resources the tree has are really compromised. So the beetle numbers are going up as a result of the drought-stressed issue in those tree species.”
Every year since 1947, DNR flies above forests across the state to survey the trees and analyze how many are dead.
DNR then publishes its findings in an annual report. The 2022 report surveyed 22 million forested acres in Washington. That report shows that “the area with mortality caused by pine bark beetles in 2022 was approximately 123,700 acres. Mountain pine beetle damage increased from 53,100 acres in 2021 to approximately 76,800 acres in 2022. The majority of annual pine bark beetle mortality is in lodgepole pine killed by mountain pine beetle, which totaled 66,800 acres in 2022.”
Also, the report shows mortality of ponderosa pine due to western pine beetle has increased steadily since 2012 and reached a peak of approximately 44,300 acres in 2022, the highest level since 2006.
Plus, mortality due to Douglas-fir beetle has been increasing in recent years, reaching a 10-year high of approximately 105,000 acres in 2022.
Kohler said these trends will likely continue as long as current environmental factors stay the same.
“As long as there’s susceptible hosts out there, the drought continues, and other factors that are keeping their populations high continue, then we’re just going to see more and more acres with bark beetle mortality,” he said.
There are solutions, though. Katie Zander, a service forester for DNR, helps private owners maintain their properties to prevent impacts from bark beetles and ultimately wildfires.
“There's very little interaction with their forest land so having a service forester out to help those landowners really help them get a plan in place and know which steps to take next to reduce the forest fuels and increase forest health,” said Zander.
She said in the last year, they’ve been able to increase their impact thanks to new funding. House Bill 1168 passed in 2021 and provides $125 million every two years to help increase wildland fire response and accelerate treatments.
She said the southeast region of Washington’s DNR has treated more acres this year than ever before and spent double the amount in the last two years combined.
Her big advice to private owners is to clear the base of their trees, keeping the greenery higher up. This can save a tree if a fire starts.
“These ladder fuels, whether it’s a low hanging branch that’s getting down to the ground, a short tree that’s meeting up to some low hanging branches, or some brush growing into the canopies of the trees, that's what we’re looking to reduce out on these properties,” said Zander.
If homeowners need financial help clearing their land, that’s where she and her team step in to see how they can help pay for the project.
She said her goal is to make sure private land is as clear as possible, which will ultimately help the whole state.
“All of these forest health treatments really add up together," Zander said. "That's really what we’re looking to do out here. Not just one individual or a shotgun approach of a landowner here or an agency there doing work. We need to all have cross-boundary work.”