The number of Medicine Bow National Forest lodgepole pines stricken by the mountain pine beetle probably doubled between 2006 and 2007, a U.S. Forest Service spokesman said.

Because the number of affected acres in 2006 was 75,000, the Medicine Bow's lodgepole forest of 350,000 acres has likely lost close to 150,000 acres, with more to come.

That grim assessment by Clint Kyhl, the forest's beetle team leader, came on the heels of a Denver press conference on Monday during which officials predicted that Colorado's northern forests will be entirely killed off by pine beetles and spruce beetles within the next three to five years.

Officials said the beetle infestation has been concentrated in five northern Colorado counties straddling the Continental Divide and has since spread to the Front Range and southern Wyoming.

Monday's press conference did not include details of the spread in Wyoming. Kyhl said the Medicine Bow will hold a bark beetle workshop in Laramie on Feb. 6, and the Legislature's Joint Agriculture Committee will receive a statewide beetle briefing on Feb. 14 in Cheyenne.

In Colorado, the infestation that was first detected in 1996 grew by half a million acres last year, bringing the total number of acres attacked by bark beetles to 1.5 million, state and federal forestry officials said.

"This is an unprecedented event," said Rick Cables, Rocky Mountain regional forester for the Forest Service in Denver.

Erik Molvar, a wildlife biologist with Biodiversity Conservation Alliance in Laramie, said the beetle infestations are roaring on unabated due to climate change.

"These infestations take place naturally on 20- to 40-year cycles," he said. "In the past, they've run their course until a bitterly cold winter took place. Studies show that you need a two-week cold snap at minus 20 degrees Fahrenheit to kill off the beetles. Nothing else works."

Kyhl said lodgepole infestations hit southern Wyoming's Sierra Madre Mountains last year, so residents of Saratoga and Encampment have seen plenty of dead and dying trees. Beetles can fly several miles to infest new stands of trees, he said, and their distribution is aided by Wyoming's strong winds.

"The beetles are moving north from Fox Park, toward the scenic byway, so folks in Albany and Centennial will be noticing dead and dying trees," he said.

Medicine Bow staffers are spraying high-value trees in campgrounds to keep them beetle free, Kyhl said. In addition, there's hazardous tree removal from campgrounds, fuel reduction from the wildland/urban interface around homes and some timber cutting.

Molvar said that short of cutting down every tree in the forest - which would be even more damaging than beetle kill - nothing can be done to stop or even slow the spread of bark beetles. Nothing short of a cold snap, that is.

"I doubt we're going to see anything like that soon," he said.

The fire potential will increase as trees retain their needles for a couple of years after beetles attack, said Bob Kane, regional entomologist with the Rocky Mountain Region of the Forest Service. When the needles fall, the danger will decrease, and spike again when the trees fall in about 10 years, Kane said.

Molvar said fire danger peaks while the dead needles are still on the tree, but declines thereafter. "There's no well-established link between beetle kill and wildfire," he said.

About 8 percent of forest landscape in Colorado consists of lodgepoles, said Ingrid Aguayo, forest entomologist with the Colorado State Forest Service. Aguayo said the epidemic doesn't mean it's the end for lodgepoles, but rather part of the regeneration process.

"A lot of people think this is the end of the forest, but as an entomologist, I see it as the beginning," she said, pointing out seedlings about five inches tall are already sprouting in parts where the beetles have run their course.

"It's not going to be a moon landscape like a lot of people think," she said.

In some cases entire mountainsides can be turned red as trees struggle to survive the infestation, affecting the scenic vistas along stretches of mountain highways. Eventually the trees will turn gray after the needles fall, Kane said.

It could be up to 50 years before lodgepoles return to their population before the bark beetle infestation, Aguayo said.

Jim Maxwell, a spokesman for the U.S. Forest Service, said the lack of trees will increase the water supply by 30 percent on national forest lands for about 20 years because trees will no longer be pumping water out of the soil.