Toppled trees provide primo bark beetle habitat, prompting temporary Mineral Ridge recreation area closure
As the trail switchbacked and gained elevation, the damage from January’s windstorm appeared.
“This is where it starts to pick up,” said Debbie Paul, a Bureau of Land Management forester in Coeur d’Alene.
Paul was hiking the Mineral Ridge National Recreation Trail, a popular 3.3-mile trail near Coeur d’Alene, in late February. A massive January windstorm toppled hundreds of trees in the 206-acre recreation area. Wind gusts as high as 61 mph splintered and ripped mostly Douglas fir and grand fir trees from the ground. Now these trees are scattered like matchsticks across the hillside.
“I mean, it looks like a bomb went off in here,” Paul said.
The story was similar across the region; 70 mph winds in Spokane toppled about 200 trees on Spokane Parks and Recreation land. More than 150 trees fell on Tubbs Hill, another popular hiking area in Coeur d’Alene. Fallen trees knocked out power for thousands and killed two.
In the moment, those falling trees posed plenty of danger – to people and infrastructure. But now, months later, they continue to pose a threat, albeit a time-delayed and ecological one.
Bark beetles.
These tiny, hard-shelled insects reproduce under the bark of trees. There are more than 600 species of bark beetles in the United States. Through the long tango of evolution, native trees have developed defensive techniques to keep the tiny invaders at bay.
“A lot of times we think, ‘Oh, the poor tree and the big, bad bark beetle,’ ” said Danielle Malesky, an entomologist with the Forest Service based in Coeur d’Alene. “But in actuality, trees have a whole host of defenses to fight the bark beetle.”
Living trees at least.
Fallen trees, like those scattered across Mineral Ridge, provide prime habitat for the beetles and can spur a bark beetle outbreak the following year. That’s one of the reasons the BLM plans to close the Mineral Ridge Scenic Area next week to remove the fallen trees. The removal will target 35 acres and is also intended to reduce fire fuels.
“We really don’t want this site to be impacted by bugs,” said Suzanne Endsley, a spokeswoman for the BLM in Coeur d’Alene.
It’s unclear how many trees fell across the region during January’s windstorm and the smaller windstorm in late March.
The Idaho Panhandle National Forest “does not have any comprehensive tracking effort underway,” spokesman Patrick Lairs said.
For urban forests, the risk of a bark beetle outbreak is low as fallen trees and branches are quickly removed, said Katie Kosanke, Spokane Parks and Recreation’s urban forester.
Large slash piles, however, like the one north of I-90 in East Central Spokane, could pose some danger.
“I had also been in touch with streets about the debris pile by the freeway and encouraged them to also dispose of it quickly for this reason,” Kosanke said in an email. “I believe the majority of it is now gone.”
For example, a 1939 windstorm over Colorado’s White River Plateau led to a spruce beetle outbreak that killed Engelmann spruce trees and some lodgepole pine totaling 10 million cubic meters of wood. In the 1950s, winds in western Oregon and Washington toppled 27 million cubic meters of forest. Following those storms Douglas-fir beetles killed another 8.3 million cubic meters.
“Generations of bark beetles will start leaving the downed materials, and if the population pressure is high enough, they will start attacking nearby trees,” Malesky said.
It doesn’t always happen that way.
The specific conditions that cause an outbreak vary. In general, it depends on the timing and extent of the wind. Dried out trees provide poor habitat for beetles, for example. The pine engraver and Douglas fir beetles found at Mineral Ridge tend to start flying after the first 60-degree day, Malesky said.
Other variables include the presence of other stressors (drought or root disease, for example), precipitation and the types of trees in the impacted area.
“Bark beetles are tree-species specific and have preferred tree sizes and forest conditions,” Malesky said in an email.
Those two variables – root disease and the type of tree – played major roles in this year’s windstorms.
Mineral Ridge, and the region in general, was once dominated by western white pines, ponderosa pines and western larch. These trees had evolved to be “highly tolerant of our native root diseases,” said Christy Cleaver, a plant pathologist for the U.S. Forest Service.
But since white pine blister rust was imported to North America on nursery trees, native western white pine populations have plummeted. Fire suppression has also hurt ponderosa pine and western larches, which require more sunlight than grand firs or Douglas firs.
“The once white pine-dominated forests have shifted now to grand fir and Douglas fir,” Cleaver said. “The tree species that are highly susceptible to the root diseases.”
Root diseases weaken the roots of trees. Compounding the issue is January’s windstorm occurred during a relatively mild and wet winter.
“It hadn’t been super cold. We had a lot of rain prior to that,” Cleaver said. “And the ground wasn’t frozen. It caused the ground to be saturated, which can also lead to wind throw in even healthy trees.”
In this cycle, native trees are decimated by nonnative fungus and fire suppression. A new tree species fills the gap but isn’t as resistant to native root diseases. A windstorm roars in and – aided by a mild and wet winter – downs these poorly adhered trees. All of which provides habitat for bark beetles.
At the same time, bark beetles have expanded their range.
That expansion, scientists believe, is due to climate change. Traditionally, bark beetle numbers were held in check by cold winters that would periodically kill the insects. Those kind of winters are becoming less common. Meanwhile, a warming climate and the ongoing drought in the West is stressing many U.S. tree species.
That, in turn, makes them more susceptible to beetle attacks.
Bark beetles have ravaged 85,000 square miles of forest in the western United States since 2000, according to a 2019 Forest Service report. Decades of fire suppression have led to dense and relatively homogeneous forests – which makes life easier for bark beetles.
“It’s nice to have a diverse landscapes,” Cleaver said.
That offers a silver lining, at least in the case of Mineral Ridge.
Prior to the windstorm, the BLM had no plans to thin trees on Mineral Ridge. The area is popular, receiving more than 60,000 visitors a year, Endsley said, which makes closing the site and selectively logging difficult.
The last time the site was managed in that way was in the 1990s, although the BLM has tried to reduce fire fuels since then.
After BLM contractors remove the downed trees this month, foresters will evaluate the area and possibly plant pines and spruce next year, Endsley said.
“If this didn’t happen, we wouldn’t be treating this,” Paul said.
While it’s certainly sobering to see so many downed trees, Paul said wind, like fire, is fulfilling an important ecological role.
“This is Mother Nature’s way of taking care of the forest,” she said.