The U.S. Forest Service is putting the finishing touches on its annual report on how the region's forests are holding up against an ongoing multi-pronged attack from a variety of beetles, worms and other pests.
The results are a mixed bag.
The good news is a few years of drought relief have helped push the Douglas fir beetle back on its heels. Numbers of the Western balsam bark beetle and fir engraver beetle appeared to drop off as well.
“Most of the Douglas fir beetle activity appears to have decreased some last year,” said Greg DeNitto, group leader of the Forest Service's Northern Region forest health protection team. “The increased moisture of the last couple of years has improved growing conditions.”
That's been enough to give Douglas fir a fighting chance. When trees are healthy, they can sometimes ward off an attack by beetles with a good dose of pitch.
Ponderosa, lodgepole, limber and white bark pines haven't been as fortunate. Around Montana, mountain pine beetle infestations have been spreading in huge concentric circles from their initial points of attack.
“In some areas we're seeing a decrease in intensity of the infestation just because the beetle's food source has been depleted,” DeNitto said. “They've essentially eaten themselves out of house and home - and now they're moving outward into new areas. From the air, it almost looks like a doughnut.”
There's no reason to think the mountain pine beetle infestation is winding down. It typically takes a couple of weeks of severely cold weather to knock back their numbers.
“That's something we haven't had for I don't know how many years,” DeNitto said.
Last summer, DeNitto's crews mapped 813,000 acres of pine forest with the telltale red needles that mark a recent mountain beetle infestation. That figure was down from the 820,000 acres mapped the previous summer, but there's no reason to celebrate.
“We weren't able to fly as much this summer because of the fire season,” he said. “There was a significant amount of area infested by the mountain pine beetle in western Montana and northern Idaho where we were unable to fly.”
The mapping crews had better luck farther south where they found a dramatic jump in acreage infested by the Western spruce budworm.
Last summer, 1.12 million acres of forests in Montana were affected by the insect that consumes the needles of Douglas fir trees. In 2005, the agency mapped 449,000 acres infested by the bug, which in itself was a striking increase from 2004 when 177,000 acres were affected.
The national forests hit hardest by the Western spruce budworm include the Gallatin, Helena and Beaverhead-Deerlodge.
DeNitto said the situation can change quickly.
“One good cold weather snap this spring that coincides with the budworms coming out of their winter hideaways can knock them back,” DeNitto said. “They can literally almost disappear in a week.”
All of the bark beetles and the budworm are native to Montana, but these widespread infestations aren't typical.
“The condition of our forests today is what makes them susceptible to these kinds of infestations,” DeNitto said. “It's basically the same kinds of conditions that make them susceptible to fire.”
Many of Montana's forests are overgrown and filled with trees that are close in age. Sometimes the species of trees has changed over time.
“Mountain pine beetle infestations in lodgepole are probably routine, but the Douglas fir and spruce budworm is certainly exacerbated by the kind of multistoried, multilayered stands that make it very susceptible to the budworm,” he said.
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