ONLY A DECADE AGO, towering spruce trees shaded the runs at Brian Head resort, a picturesque ski area perched above red-rock cliffs in southwestern Utah. Then came the beetles. After a series of windstorms in the early 1990s toppled an unusually high number of trees, bark beetles proliferated in the deadfall. In 1994, they began to overwhelm and kill healthy trees on Cedar Mountain, where Brian Head is located.
Over the next 10 years, beetles killed up to 90 percent of the spruce trees across 30,000 acres of Cedar Mountain, including most of the trees at Brian Head. The spruce needles turned red and fell off, exposing "ghost forests of standing deadwood. To reduce the risk of fires and to protect skiers from falling limbs and trunks, logging crews began removing dead and diseased trees. By the time the infestation ended, areas of the resort looked as if they were above treeline. "It used to be a big, beautiful, thick green forest," says mountain manager Mac Hatch, who's worked at the resort since the mid-1980s. "Now there are just patches of spruce."
If you ski in the West, what hit Brian Head could happen at one of your favorite resorts. With astonishing ferocity, several bark beetle species are devouring conifers across millions of acres of forest in western North America. You can find epidemics in Colorado's Vail Valley; in the lodgepole pine forests around Breckenridge; throughout Grand County, home to Winter Park; and in the Stanley Basin north of Sun Valley, Idaho.
Besides being unsightly, a tree die-off can harm a ski operation in a number of ways. With fewer trees to block the wind, Brian Head has had more lift closures. The loss of trees also makes steep runs more avalanche-prone. But the most frequent damage is to the texture and depth of snow, and is caused by something usually warmly welcomed by skiers: sunshine. "Snowpack that's under a tree canopy has less solar radiation on top of it," says Brian McInerney, a National Weather Service hydrologist in Salt Lake City. "As a result, it doesn't ripen as fast and it will last longer into the spring."
A certain amount of tree-kill by beetles is natural. After all, bark beetles have fed on the cambium (new growth below the bark) of trees for eons, helping cull forests of weak trees. But today's infestations are unusually virulent. Pine beetles are spreading north, reaching loftier elevations and killing trees on a scale never witnessed before. "Just about any way you measure it, what's going on with bark beetles is remarkable," says Jesse Logan, an entomologist at the U.S. Forest Service Rocky Mountain Research Station in Utah.
Foresters offer several reasons for the surge. Decades of fire suppression have caused many forests to grow uniformly old and dense. Like aging animals in the wild, old trees more easily succumb to disease and predators. In dense stands, they must also compete for scarce water and light. Meanwhile, beetles easily commute between tightly grouped trees. And an ongoing drought has made trees more vulnerable. Trees ooze sap to repel beetles, but during droughts, less sap flows, allowing beetles easier access to the cambium.
Logan points out that many of the infestations began when temperatures began rising in the West in the mid-1980s. His research indicates that when temperatures rise as little as two degrees, bark beetles are more likely to complete their life cycle in one year, rather than two years or longer. The shorter cycle means beetles spend less time in stages where they're likely to be picked off by predators such as birds or killed by deep freezes. Most important, the entire beetle population hatches together every summer. "To overcome a healthy tree, thousands of beetles have to attack it, so synchrony of emergence is really important," Logan says.
Besides deep freezes, fires reinvigorate forests and make trees less vulnerable. Another limiting factor are the beetles themselves: Once they run out of food, they die off and the infestations subside.
Since none of these options is popular with ski area managers, many have begun working with the U.S. Forest Service to shore up their trees' natural defenses. At Sugar Bowl, Calif., logging crews are thinning overly dense stands. Workers at Jackson Hole, Wyo., are applying packets of beetle-repelling pheromones to whitebark pines. At Sun Valley, Idaho, new trees of various species have been planted. Because each beetle species tends to feed exclusively on a single type of conifer, diverse forests are less likely to be wiped out.
Where beetles are especially vigorous, ski areas are taking more aggressive actions. Patrollers at Winter Park, Colo., have been trained to recognize infected trees—signs include large bubbles of pitch and piles of sawdust—and tag the trees for removal. At Steamboat, resort workers and the Forest Service are cutting and peeling infected trees and using traps. (Spraying is effective, but it costs roughly $10 per tree and must be repeated annually.)
So far, Steamboat and Winter Park have managed to protect most of their trees. But Logan believes that if temperatures stay above normal, many more national forests—and the ski areas inside them—may come to resemble balding Brian Head. Stopping the worst infestations, he says, will be "like trying to turn back a hurricane with a giant fan."