These are good days if you're a tree-killing bark beetle.
In 2007, the native pests ate deeper into the region's drought-weakened forests, choking the life out millions of trees in one of the largest outbreaks in decades.
In some places, the rate of spread slowed down, but that may be primarily because the insects ran out of live host trees, said Ken Gibson, an entomologist with the U.S. Forest Service in Missoula.
Elsewhere, the bark beetles have kicked it up a notch, including in high-elevation whitebark pine trees, which are an important food source for grizzly bears in and around Yellowstone National Park and which help control the flow of the region's melting snowpack.
The end of the infestation may not come with the end of the drought, which is now in its eighth year, but when the rapacious beetles, each smaller than a grain of rice, run out of trees to ravage, Gibson said.
The beetles in parts of Montana and Wyoming have been in a frenzy since the late 1990s, part of a larger trend from Arizona to Alaska, where milder winters allow them to survive and breed faster to attack thirsty trees that don't have the same defenses as they would during wetter periods.
The beetles are one of nature's native regulators, perpetuating life-and-death cycles and spurring nutrient recycling.
They typically kill a tree by boring through the bark and mounting a large-scale occupation that stifles the flow of nutrients.
They go through periodic outbreaks, including those in the Yellowstone area in the 1930s and 1970s, but the latest event is odd because so many species are flourishing at once: mountain pine beetles, Douglas fir beetles, western balsam bark beetle and others.
"It seems like it's usually one or the other," said Roy Renkin, a vegetation expert in Yellowstone.
Forest officials thought the bugs might be on the decline after parts of Western Montana and Idaho saw near-normal amounts of precipitation in 2005 and 2006.
But last year, warmer and drier conditions set in again and more than 1 million acres were beset by beetles, said Gibson, who compiles an annual tally of aerial surveys looking at beetle kills.
The actual number is probably higher because only about 70 percent of the region was surveyed, Gibson said.
The shiny black-shelled mountain pine beetle is doing the most damage, occupying more than 891,000 acres and killing about 2.7 million trees, mostly lodgepole pine, including in Yellowstone.
"What struck me about the mountain pine beetle is the increased activity in the lower-elevation lodgepole," Renkin said.
Of particular concern is the effect the beetle is having on whitebark pine stands in and around Yellowstone.
In some places, such as around Avalanche Peak in the park's southeastern corner, the beetles killed more than 170 whitebark pine trees per acre, roughly 96 percent, within two to three years.
Mortality among whitebark pine increased in most places in 2007 as 66,700 trees were killed across 37,000 acres in Yellowstone, according to Gibson's report.
Some have theorized that warming climate conditions have made it easier for the beetles to arrive and thrive at higher elevations and to survive winters, which is typically a time when they die in long cold snaps.
Many of those trees are facing a double-whammy, coming under threat also from blister rust, a non-native fungus that can be fatal to the trees.
That one-two punch is cause for concern among some, not only for the trees but also for the bears, squirrels and the Clark's nutcracker that eat its high-protein nut and the alpine ecosystems that depend on it for soil stability and water release.
"I don't think the picture is much improved," said Diana Tomback, a biology professor at the University of Colorado at Denver and director of the Whitebark Pine Ecosystem Foundation.
She and others in the region are looking at ways to restore whitebark pine and to find trees that are naturally resistant to blister rust that might later play a role in re-establishing the species at high elevation.
"There are more and more people on board with the realization that restoration has to happen," she said. "But the bottom line is all the planning in the world is not going to bear fruit unless there's funding."
There is no known method to kill bark beetles on a large scale. Patches that emit a pheromone are effective at keeping beetles out of individual trees. That's being used in some places around the region.
Renkin cautions against a "doom and gloom" attitude, however. The beetles have done this before and will probably do it again, he said.
Beetle outbreaks increase the risk of fire by about 11 percent, according to some recent data crunching, and that's typically about 15 years after the outbreak, Renkin said.
Gibson also expects the beetles to go into a lull again, but it's hard to say when. Plenty of moisture may help trees put up a better defense this summer, he said.
"But if we get continued warm and dry weather, the population is just going to continue," Gibson said.The Billings Gazette
