Attack of the bark beetles

  • A Douglas fir shows sign of a beetle infestation more than a year after an attack

    Deborah Hill
  • A bark beetle at work

    USDA Forest Service
 

ISLAND PARK, Idaho - Oblivious to the dry summer heat, Forest Service silviculturist John Councilman hikes through a stand of trees looking for signs of violent struggle. It doesn't take long.

"There's a beetle hit," he says, pointing out a Douglas fir drizzled with thick threads of dull yellow pitch. "That tree is already dead. It just doesn't know it yet."

Sprawling across 1.8 million acres in southeastern Idaho and western Wyoming, Targhee National Forest is suffering through its worst Douglas fir bark beetle attack since 1990. "At first we thought, great, we need more gray snags," says Councilman, who works with the U.S. Forest Service in Island Park. "Now we're getting a little worried."

Snags, or standing dead trees, create habitat for plants, birds and small animals, but more than two or three per acre make the forest susceptible to lightning-sparked fires. In the Targhee, Councilman says, beetle numbers have steadily increased since 1999.

Mercilessly hot conditions in the drought-stressed West have aggravated a variety of insect invasions, from a Mormon cricket takeover in Utah to a grasshopper epidemic in Alberta, Canada. But bark beetles (in several species) are the top pest, having destroyed an estimated 82,300 acres of trees in western Montana, 500,000 acres in Northern Colorado, and swaths of forests in Washington, northern New Mexico and California's Sierra Nevada. Here, in Idaho's Sawtooth, Salmon-Challis, Caribou, Targhee and Nez Perce forests, and in the Centennial Mountain Range, the beetles seem unstoppable.

Called in to determine if the Targhee infestation has finally peaked, U.S. Department of Agriculture entomologist Ralph Thier isn't optimistic. "I'd say we're not done with these bugs just yet," he says. "People come to the forest and revel in how peaceful and natural it seems, but it's a war zone here."

Despite this, both Thier and Councilman join local conservationists in thinking that perhaps the best response to the epidemic is to do nothing at all.

It's a beetle thing

To understand a beetle infestation, one must understand the beetles.

More than 114 bark beetle species live in Idaho, but only a handful destroy trees. The killer Douglas fir bark beetle is always present here - in a healthy forest - in low numbers.

The beetle's cycle kicks off in early May, when the black, rice-sized insects burrow through the outer bark of mature trees, usually over 14 inches in diameter, and penetrate the soft inner bark, or phloem. In response, some trees try to flood the bugs out with copious streams of pitch.

"But if the beetle populations are high enough," says Thier, "they can overwhelm a tree in two to three days."

Blown-down trees are a welcome sight to bark beetles, which prefer freshly fallen green trees. The Douglas fir infestation in Idaho's Panhandle National Forest was launched by an ice storm in 1996. In Steamboat Springs, Colo., a 1997 "blowdown" of 13,000 acres of spruce started a 500,000-acre buffet that's still swarming.

But as this year has demonstrated, drought, which stresses even healthy trees, increases their vulnerability to insects: No water, no pitch, so the beetles have an easy entree. Researchers also believe that stressed trees may produce a scent that attracts the insects.

Tracking beetles, however, can be difficult. The Forest Service monitors beetle damage by flying over the forest, searching for the bright reddish-brown needles of infested Douglas firs. Unfortunately, the trees' needles don't turn brown until a year after a beetle attack, making it tough to judge the severity of an infestation in real time. Right now, officials know that the number of dead trees in Targhee National Forest increased from just over 200 in 1997 to more than 12,500 in 2001.

Ultimately, though, most beetles are beneficial, Councilman says. Douglas fir beetles tend to kill trees in patches, which helps to thin the forest, allowing sunlight to filter down to other species of trees and brush. Douglas fir beetle population booms normally run their course in three to four years.

Other beetles, such as the mountain pine beetle, are more damaging to the forest because they kill off entire stands of trees. But on the whole, beetles, like fire, are an integral part of the forest ecosystem.

"Considering just how out of balance our forests are now," says Thier, "this is normal."

They're here. Now what?

Inevitably, where there's a beetle infestation, there's controversy about what should be done.

In 1978 on the Targhee, the Forest Service approved clear-cutting in order to stem a similar epidemic. The campaign, which lasted for 20 years, introduced thousands of miles of logging roads, impacting critical grizzly, raptor and elk habitat (HCN, 11/8/99).

The Forest Service repeated the clear-cut approach in other parts of Idaho. On the Payette and Boise national forests, conservationists said the "epidemic" was only an agency fabrication, designed to justify logging.

The current situation on the Targhee shows that clear-cutting actually aggravates the problem. Forests replanted in clear-cuts tend to be more homogenous, which concentrates and increases the species-specific beetle population. "You can't cure the problem by cutting all the trees down," says Marv Hoyt, with the Greater Yellowstone Coalition.

But tourists don't come to places like Island Park to see dead trees, so there is often local opposition to letting an insect outbreak run its course.

"It's clear that we manage our forests based on human values, and people like lush stands of trees," Councilman says. Many areas within the Targhee would benefit from judicious thinning, he believes, but officials tiptoe around the suggestion.

There may be a less-intrusive alternative in the works, in the form of a synthesized pheromone. The substance is a man-made copy of the chemicals that insects use to communicate with each other, and it simply shoos away the beetles, rather than decimating them. This would allow foresters to protect already-weakened stands and reduce insect populations to more manageable numbers.

The Forest Service hopes to deploy the pheromone in the Targhee National Forest by 2003.

 

Deborah Hill writes from Idaho Falls, Idaho.