Bark beetles cutting swath through Mount Hood pines

PARKDALE, Ore. — On the pine-covered slopes of Mount Hood, a rice-size beetle larva is turning pines to a rusty red, killing them by the thousands.

The squirming, white, bark beetle larvae are chewing through tissue that carries nutrients up the tree. The beetles are nothing new, but are showing up in unusually huge numbers.

Experts estimate they killed at least 145,000 trees just in the Mount Hood National Forest last year, and as many or more this year, the worst infestation in 50 years.

It's part of a natural cycle streaking the Cascade Range. Statewide, beetles went after 570,000 acres of forest in 2003 and 710,000 acres in 2004.

The beetles kill aging trees and make way for wildfires to clear room for new forests. Foresters say fire suppression and climate changes may have a hand in today's beetle boom.

The bugs are doing damage across the country and in Canada. Scientists suspect those outbreaks may be tied to global warming, helping them survive where cold weather once controlled them.

Warming is not the certain culprit in the Cascades. Temperatures aren't as cold there to begin with, and beetles are a longtime resident.

But warming and the dry years the Northwest has seen lately put trees under greater stress and accelerate a beetle onslaught, experts say.

"There's probably some contribution warming is making; we just can't put our finger on it," said Andy Eglitis, a Forest Service entomologist based in Bend.

The beetles' prime targets are skinny and short-lived lodgepole pines that grow at higher altitudes and burn up in big fires. Many lodgepoles on Mount Hood took root after fires nearly a century ago. They're now perhaps 80 or more years old, about as big as they're going to get, and face rising stress as they crowd one another for light, water and nutrients.

Stressed trees emit chemical signals that lure beetles, who bore through the bark of the biggest trees to lay eggs. They release their own chemical beacons to rally others. Healthy trees fight them off with gobs of sap, but aging, strained trees cannot.

Usually beetles kill a tree within a year.

Whitebark pines already hammered by blister rust are being killed by beetles. Almost all the lodgepole pines around Olallie Butte at the south end of the Mount Hood National Forest have died.

Another form of bark beetle has gone after Douglas firs across the forest. Ponderosa pines, especially dense stands planted after clear-cutting decades ago, are at risk, too.

Foresters used to try halting outbreaks by cutting down infested trees and burning them, or spraying them with chemicals, but never succeeded.

"There's not a single shred of evidence you can control them," said Scott Hoffman Black, an insect expert and executive director of the Xerces Society, an insect conservation group based in Portland.

Forest managers long tried to keep fires from sweeping through aging stands, but that may have compounded the problem. Blazes might have split the landscape into a patchwork of varying ages, some inviting to beetles but others not.

Today, however, the beetles have vast, unbroken swaths of forest, so they can spread and multiply nonstop.

Loggers are salvaging some dying trees, often for firewood.