Todd Hartman
Rocky Mountain News

BOULDER, Colo. — Every large, mature lodgepole pine forest in Colorado and southern Wyoming will be dead within three to five years, killed in a mountain pine beetle infestation unprecedented in the state.

In 2007 alone, the infestation once centered on the Western Slope tore through another 500,000 high-elevation acres and embedded itself along the Front Range, exploding in Boulder and Larimer counties where affected acres grew by 1,500 percent.

State and federal foresters, calling the numbers "catastrophic," said recent aerial surveys reveal the dead and dying lodgepole acreage now has grown to 1.5 million since the first signs of outbreak in 1996.

With 22 million acres of forest in Colorado, the beetles won't kill it all, but they could do away with most of the "pure lodgepole" stands as well as many of the trees within mixed systems of lodgepole, spruce, fir and ponderosa that cover several million acres in the state.

It will take decades for the stands to return.

Rick Cables, the U.S. Forest Service's regional supervisor described the die-off as "a huge, unprecedented event" with major social and economic implications.

Rapid spread stunning

Perhaps most at stake are the state's water supplies. A lack of soil cover and the potential for forest fires as the dying trees dry out could leave reservoirs and rivers clogged with sediment more likely to pour off the landscape.

Recreation, too, is jeopardized, as campers and skiers are faced with spending their vacation time amid red-needled trees, or those with no needles at all.

Backcountry hikers will need to be more cautious about falling trees and mountain town economies could also be hurt by a browning backdrop less alluring to visitors.

The extent of the spread stunned even foresters who say the invasion is rewriting the scientific literature. Centuries-old lodgepole at the highest elevations, once seen as impregnable because of extremely cold temperatures that kill the beetles, are dying.

"We were surprised by the spread into high-latitude forests - it was very uncharacteristic for the mountain pine beetle to go that high up in elevation," said Susan Gray, a specialist in forest health for the Forest Service.

Colorado State Forester Jeff Jahnke blamed "an unprecedented combination of drought and warm winters" for stressing the trees and leaving them especially open to beetle-infiltration and too weak to ward off attacks.

Indeed, other pine beetle outbreaks have collapsed after weeks-long cold spells with temperatures under 20 degrees below zero. But Gray said it hasn't been cold enough long enough, to kill the sturdy, rice-sized beetles.

A natural process

Gray said the prediction of a complete die-off within three to five years is based on the infestation's current rate of spread and intensity. She said it covers the entire range of the tree in Colorado and southern Wyoming.

In other places, including parts of Summit and Grand counties, the pine beetle has so ravaged the forest that the infestation is finished, "because the host trees are already dead," Gray said.

Cables, however, emphasized that what is occurring is in many ways a natural event, fueled in part by uniformly older lodgepole forests and the role of the beetle in thinning.

He compared the situation to having a human population made up entirely of people in their 70s and 80s, when disease begins to affect large numbers.

"Mountain pine beetles are an agent of regeneration," Cables said.

He said the die-off is a reminder for forest managers of the need to use controlled fire and other means to create a "diversity of age classes" so that "one insect or one pathogen cannot destroy an entire forest at once."

Indeed, even as the outbreak moves into the Front Range's ponderosa pine forests, it's unlikely to create the same visual devastation as on the Western Slope. The ponderosa forests tend to have a better mix of tree species, as well as more age diversity, making it unlikely the beetles will find as many suitable hosts as in the pure 80-plus year-old lodgepole stands it has favored.

Trying to stop or even slow the infestation is a fool's errand, scientists say. Instead, local communities, landowners and the Forest Service can only target pockets where dead forests would pose a fire risk to homes, towns and water supplies. But those efforts total just tens of thousands of acres.

Copyright 2008 Denver Publishing Company