May 18, 2004
Last modified May 18, 2004 - 1:37 am
Tree-killing beetles more deadly than wildfires
The tiny architects of the Western forests are coming back.
In coming weeks, an army of tree-killing beetles will begin emerging, looking to satisfy their appetites by boring into lodgepole, Douglas fir, whitebark pine, Engelmann spruce and other trees in the Rocky Mountains.
Their defenses weakened by drought, thousands upon thousands of trees won't have the strength to battle the bugs and will eventually die. By the time they're through, the beetles will have a larger impact on Western forests than wildfire, said Diana Six, an associate professor of forest entomology and pathology at the University of Montana.
"We're seeing more outbreaks than we've ever seen," Six said.
Bark and pine beetles, about the size of pencil erasers, are one of nature's resident regulators, thinning forests when trees get too old or too weak.
But the sixth year of drought in the West has left scores of water-starved trees without the ability to produce sap or chemicals to keep the beetles at bay. In Montana, Wyoming and elsewhere in the Rockies, researchers expect the beetles to kill more trees this summer than in the last few years.
In 2003, nearly a half-million acres of forest were impacted by bark beetles in Montana, including 305,000 acres by the mountain pine beetle and 76,000 acres by the Douglas fir beetle. At Yellowstone National Park, some 15,100 acres of whitebark pine - whose nut is a key source of food for grizzly bears - were hit by the mountain pine beetle. Spruce beetles ate through more than 8,000 acres of Engelmann in the park.
Those figures have increased nearly every year since 1998 and likely underestimate the effects of beetles because aerial surveying methods can be hampered by wildfire smoke and other factors.
"It's definitely underreported," said Gregg DeNitto, who leads the forest health group for the U.S. Forest Service's Region One branch in Missoula. "And our expectation is we're going to see an increasing amount of mortality."
It's not unusual for one species of beetle to flourish briefly in the right conditions. What's odd in the last several years is that several kinds of beetles are infesting large swaths of forest in several states.
"This is truly unprecedented activity in bark beetles from Alaska to southern Arizona," said Jesse Logan, a Forest Service research scientist based in Logan, Utah. "It becomes pretty astounding, really."
In northwest Wyoming, bark beetles have occupied the north fork of the Shoshone River and Carter Mountain outside of Cody and left behind thousands of dead trees.
Shoshone National Forest officials closed five campgrounds this year to help free up $200,000 for "fuel reduction" projects targeting areas prone to wildfire and damaged by bark beetles.
"The heavy fuels are already there. When the bark beetles kill the trees, there's increased fire danger," said Gordon Warren, a Shoshone forest spokesman.
The beetle outbreak was only exacerbated by this year's relatively mild winter and a continuing lack of moisture.
"We're seeing year after year of widespread stressed-out trees," Six said. "These trees just don't have a lot of fight left in them."
When a female beetle finds a struggling tree, she bores in and emits a smell that attracts other beetles. Soon, perhaps thousands are attacking the tree beneath the bark. Once the tree is dead, usually within a year, the beetles breed, lay eggs and eventually move on to the next tree.
Some scientists, including Six, said the situation also is being driven, in some way, by an overall climate change. Warmer temperatures allow the beetles to multiply faster and spend more time finding trees in the summer, Six said. In the past, mountain pine beetles were actively flying for about three weeks in the summer. Now, some emerge in May and last until September, she said.
Certain beetles also are making forays into higher elevation forests where they haven't been before.
"It's not at all like the textbook anymore," she said. "I just don't think the size and the extent of the outbreaks we're seeing are natural."
The outbreak is also being helped by denser forests, especially those that haven't had a recent fire or been thinned, and aging stands of trees that become weaker as they grow older.
Dayle Bennett, a Forest Service entomologist based in Boise, Idaho, said he isn't convinced that the latest bug activity is outside normal historic behavior.
"A lot of it is cyclic. Those beetles have been part of this forest environment for eons," Bennett said. "We have dry periods that come and go throughout geological time. … Some try to link it to global warming, but I'm not entirely sure that's the case."
Although specific areas can be treated for beetles, there is no effective way to deal with wide-ranging infestations. The outbreak probably won't subside until moisture levels increase in the West - and it will take more than just one year of average rain or snow.
"When the drought breaks, usually within a couple years those beetle populations will subside," Bennett said.
In the meantime, though, the beetles will continue to quietly reshape the forests - even while wildfires grab the headlines.
"I will say the area of forest impacted by forest insects is much greater than those impacted by fire," said Logan, adding that the fires, bugs and forests are all ultimately interrelated. "It's all a pretty complex issue."
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