A US Department of Agriculture Forest Service (USDA) contractor applies pesticides to a tree in 2005. The forests of the American West are under siege from bark beetles, miniscule but mighty foes that are ravaging the region's leading trees in record numbers.
MISSOULA, United States (AFP) - The forests of the American West are under siege from bark beetles, miniscule but mighty foes that are ravaging the region's leading trees in record numbers.
Scientists say a warming climate is behind the beetle epidemic which has killed vast swaths of spruces, pines and firs in some of the most picturesque regions of the Rocky Mountains.
Although the insects have periodically attacked Western forests, an outbreak affecting multiple tree species simultaneously in a string of states - including Colorado, Idaho, Montana, Utah and Wyoming - has no parallel.
"The main species that make up our forests are all under attack," said Barbara Bentz, entomologist with the US Forest Service's Rocky Mountain Research Station in Utah.
Studies show bark beetles are expanding their range into higher elevations, where arctic conditions once froze them out, even as a stepped-up reproductive cycle has sent their populations soaring.
"We're seeing beetles making inroads they've never made before," said Jim Rineholt, forester with the federal Forest Service.
In addition to the absence of a killing cold, the beetles have benefited from a long-standing drought that has weakened trees' defenses, and from a decades-old strategy of suppressing the wildfires that historically created a mosaic of tree types of different ages.
Officials took notice of the beetle outbreak in 2000, when the bugs destroyed a higher-than-average number of conifers.
While the beetles are smaller than the tip of a pen, they have since over-run mountain ranges, killing millions of their prime target - towering, old-growth trees.
Utah is experiencing the largest spruce beetle infestation in the lower 48 states, with the insect already gnawing through close to half its Engelmann spruce.
In Colorado, the number of lodgepole pines attacked by mountain pine beetles increased almost fivefold in 2006, rising to 4.8 million from 1.1 million in 2005. The number far exceeds the trees destroyed by wildfires or harvested by commercial loggers.
In central Idaho, bark beetles last year ate their way through 4.6 million lodgepoles and Douglas firs.
Scenic mountain views once carpeted with green now feature acres of red and dead trees that offer little benefit to wildlife and even less to the observer. From the exclusive ski resort of Vail, Colorado, to Yellowstone National Park, some of the most prized western US recreation areas are defaced with skeletal trees whose needles have browned with death.
"In some areas, we're seeing more black and brown than green," said Scott Hicswa, a private forestry consultant in Montana.
Foresters have few weapons to combat large-scale beetle infestations. They can can use chemicals to try to protect individual, high-value trees, but once a tree is under attack the battle is over.
The female beetle starts the assault. Once a suitable tree is identified, the female emits a chemical that attracts males and females, setting off a mating frenzy. The female then bores beneath the tree's bark and lays eggs as it ascends.
Hicswa says the West is facing landscape-level problems while lacking landscape-level solutions.
"We do have the tools to address the problems at an area level but we can't work as quickly as Mother Nature or at the scale," he said.
Experts can't agree how to interpret the long-term effects of the epidemic even as they concede the short-term impact is devastating.
Some researchers predict a warming West will cause infestations to worsen, turning forested peaks into barren vistas and leaving more beetle-killed trees to fuel wildfires.
Others disagree, arguing the epidemic will come to a halt when old-growth trees - which populate whole forests - have succumbed. And a recent study by university researchers in Colorado and Idaho suggests infested forests may have fewer fires because they will have less fuel to feed the flames.
US Forest Service entomologists Dayle Bennett, Steve Munson and Ken Gibson are among those who reject the "doom and gloom" scenario.
They argue that thinning of large, older trees makes way for younger, more vigorous and less disease-prone trees.
In British Columbia, beetles have laid waste to 21.5 million acres of forest and have marched eastward across the Rockies into Alberta. But findings in Canada suggest beetles have changed their habits in the absence of their preferred hosts, with some attacking smaller and younger conifers.
"The epidemic is far greater than anything we've ever seen before," said Ray Schultz, assistant deputy minister with British Columbia's Ministry of Forests and Range.