MIKE STARK Billings Gazette | Posted: Tuesday, January 23, 2007 12:00 am
BILLINGS, Mont. - Beetles smaller than a grain of rice continue to choke off and kill thousands of whitebark pine trees and other species in the Yellowstone ecosystem.
Mountain pine beetles have been hungrily burrowing into trees for years as part of a large-scale outbreak that some experts say is part of a natural cycle and others tie to global climate change.
Some had hoped that a few cold snaps last winter would have killed off many of the beetles. But when last summer rolled around, the bugs were back at it.
Roy Renkin, a vegetation expert at Yellowstone National Park, said he was taken aback last year during a trip to Avalanche Peak east of Fishing Bridge. Vast stands of whitebark pines - trees that grow in high elevations and produce a fatty nut that is an important food for grizzly bears - have been hit hard by the beetles. "It was just a red carpet," Renkin said, referring to the color needles turn as they die. "It didn't look like there was a living tree down there."
Last week the U.S. Forest Service released a report of bark beetle conditions in the Northern Rockies culled from aerial and ground surveys.
Forest fires and weather conditions kept planes grounded much of the year, so the surveys weren't as complete as hoped, said Ken Gibson, an entomologist with the Forest Service in Missoula.
The 2006 report is a mixed bag. In many places, fewer affected trees appeared in Western Montana and northern Idaho. That's probably the function of more moisture, which makes trees stronger and better able to fight off the beetles.
Last year, the mountain pine beetle swept through about 881,000 acres of forest in the region, down from more than 1 million acres estimated in 2005.
On those infested acres, about 2.4 million trees were killed, more than 80 percent of which were lodgepole pine, the report said.
While weather may have dampened some bark beetle activity, the mountain pine beetle seems to be going strong, and with no relief in sight.
"They just go through until they don't have anything left to kill," Gibson said.
The beetles occur naturally and act as a forest regulator, spurring on life-and-death cycles that kill trees - usually by digging beneath the bark in large numbers and stifling the flow of nutrients - and recycle nutrients in the forest.
Mountain pine beetles and other bark beetles go through periodic outbreaks, including those in the Yellowstone area in the 1930s and 1970s.
In recent years, large outbreaks have been recorded from Arizona to Montana and in parts of Canada and Alaska.
Among local places seeing increased activity in 2005 and 2006 are the Pryor and Beartooth mountains.
One of the top concerns in the Yellowstone area is with whitebark pine trees, a key species at high elevations.
Jesse Logan, a retired U.S. Forest Service entomologist who studied bark beetles for 30 years, said his visits to the Yellowstone ecosystem showed many places where whitebark pine infestation seems to be worsening.
The death of whitebark trees has a ripple effect. The trees play an important role in holding and controlling snow as it melts from high elevation. It also produces a high-protein nut that's important in the diet of grizzlies and other animals.
"I see what's going on in whitebark is really a true ecological threat," Logan said.
Logan said it's clear to him that the outbreak is linked to climate and man's role in making it warmer. Above-normal temperatures allow beetles to survive winters, breed faster and move to higher elevations in places where they have rarely been.
"I think the evidence is so overwhelming," Logan said of climate change.
He is pushing for an assessment of the greater Yellowstone ecosystem to look specifically at the effect of mountain pine beetles on whitebark pine.
"This is an issue that is very immediate," Logan said.
Another bug seems to be surging in Yellowstone: the spruce budworm, which crops up periodically in the area.
Renkin said about 14,000 acres in Yellowstone showed light signs of infestation. These days, it's showing in Lamar Valley, around Mammoth in the Lava Creek drainage and elsewhere.
"Now I see it wherever I go on the northern edge" of the park," Renkin said.
The budworm usually attacks new growth on trees, such as Douglas fir, and leaves behind a halo of brown needles on the outside of the crown.
It usually isn't fatal, but it can set the stage for another bug, the Douglas fir beetle, to move in for the kill.
Gibson is wondering whether the January cold snap, which included temperatures down to 40 below zero to minus 50 in higher elevations, will mean fewer beetles this summer. Even better, he said, would be a prolonged cold snap in the fall, when the beetles are more vulnerable.
It's hard to say when the outbreak will die down significantly.
"I expect 2007 is going to be another busy year for insects," Gibson said.