Wednesday, August 6, 2008

What’s killing area trees?

“Red tree” epidemic is increasingly showing itself in upper Big Wood drainage

Express Staff Writer

The small black beetle on the upper point of this hatchet—a 5-millimeter-long adult mountain pine beetle—was found in a dying whitebark pine tree on Railroad Ridge in the northeastern White Cloud Mountains. A close inspection of the peeled-away portion of the bark shows several juvenile mountain pine beetle larvae. Photo by Jason Kauffman

A red tide hailing from the north is sweeping over Galena Summit and down into the upper Big Wood River drainage northwest of Ketchum.

The naturally occurring infestation is showing itself with red-needled handiwork displayed on many stands of lodgepole pine in the drainage's uppermost elevations in the southeast corner of the Sawtooth National Recreation Area.

SNRA officials say the culprit for the increasing number of dead and dying lodgepole pine is a 5-millimeter-long native insect called Dendroctonus ponderosae, more commonly known as the mountain pine beetle. The mountain pine beetle has already been killing off upper-elevation whitebark pine trees in recent years, but the insects' spread into lower elevation lodgepole pine stands in the upper Big Wood has really begun to gain strength recently, SNRA forester Jim Rineholt said Tuesday.

A drive to the area surrounding Galena Lodge gives motorists a clear view of this emerging threat, Rineholt said.

"We're seeing more and more red trees," he said.

Mountain pine beetles are not an introduced species, but rather are native to central Idaho's forests, Rineholt said.

"They're always around in (low) endemic levels," he explained.

The major difference now is how extensive the beetle infestations have become and how the insect is affecting upper-elevation whitebark pine stands, he said. In the past, mountain pine beetles had a more difficult time getting a toehold in these high-elevation ridgetop stands because the short summer season didn't allow them to complete their lifecycles before the cold of winter arrived.

However, in recent years, longer summers have allowed the beetle to complete what was normally a two-year lifecycle in whitebark pine stands in one season, thereby contributing to their spread in these ancient and highly susceptible stands, Rineholt said.

"That's kind of the big change that scientists are seeing," he said.

Near the scenic and well-traveled Galena Summit area, the new mountain pine beetle infestations have led to a level of mortality that varies between 50 and 70 percent, Rineholt said. Charismatic, gnarled old whitebark pine trees that have survived in the brutal ridgetop elements for centuries are continuing to succumb to a beetle that is smaller than the diameter of most pens.

"That's really sad to see that," he said.

Rineholt said the dying lodgepole pine trees in the upper Big Wood are the most recent extension of a massive mountain pine beetle infestation that began killing off lodgepoles in the Sawtooth Valley in the late 1990s. He said most of the Sawtooth Valley's mature lodgepole—the preferred target for mountain pine beetle—have already succumbed. He said that's leading to the spread into the upper Big Wood as adult beetles are blown or fly into the drainage.

"They hit the wind currents and who knows where they go," he said.

Rineholt believes the infestation may not be as extensive in the upper Big Wood lodgepole pine stands as it was in the Sawtooth Valley. He said local thinning projects in the 1970s and 1980s created a forest with a much more varying age structure. That should lead to beetles' only killing off the larger trees and sparing much of the younger areas of the forest.

"I don't think we'll see that much mortality of trees," he said.

Though it's hard to see from a distance, many young whitebark pines are surviving the beetle epidemic in the Galena Summit area, Rineholt said.

"There's a lot of younger whitebark pine that are doing fine," he said.

Because trees do not begin to show red until a year after they're attacked, it's hard to know if cold snaps the area experienced last winter succeeded in slowing down the beetle spread, Rineholt said. He said the red trees people are seeing this summer are from last summer's beetle work, meaning we won't know if more trees have been killed until next year.

"I guess time will tell," he said.

Rineholt pointed out that the mountain pine beetle isn't the only insect impacting local forests. He said the Douglas fir bark beetle and the western spruce budworm are also creating damage locally.

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