Bark beetles are gnawing their way through our ponderosa-pine forests

  When Mike Wagner took Northern Arizona University students to the site where he was trapping bark beetles near Flagstaff, he expected to show them a simple lesson: Once freed from a funnel-trap, the insects would find a juniper tree and burrow into it. But as the entomologist tipped the trap, thousands of beetles poured out, making it impossible for the students not to swallow a few.

"The air was just thick with beetles," he recalls. "Everyone had beetles on their clothes. It's the worst infestation I've ever seen."

As foresters assess the damage from the tiny beetles with the deadly bite, reports indicate that this year's bugs are taking second place in the contest over which generation can kill the most trees. Last year, the deadliest year, more than a half-million acres of trees were affected by bark beetles in Arizona alone. In places like Mars Hill near Flagstaff, it's visibly clear that something is terribly wrong.

The hill, home to historic Lowell Observatory where Pluto was discovered, is in the heart of the worlds' largest contiguous ponderosa pine forest. But a great many of these trees have reddish-brown needles instead of green, an indication that, even though they are standing, they are dead. In the Prescott area, more than 80 percent of entire stands are wiped out.

Ordinarily, bark beetles infest about 5,000 acres in Arizona during the spring and summer, says Tom DeGomez, a forest-health specialist. "But last year and this year, the conditions have been extraordinary to accommodate and nurture a thriving beetle population."

Elsewhere, in places like Southern California and British Columbia, the bark beetle attack is also unprecedented. "Throughout the Rocky Mountains, it's the worst in history," says Wagner.

For researchers like Wagner, DeGomez and Wally Covington, director of the Ecological Restoration Institute at Northern Arizona University, the beetle plague was predictable -- just another chapter in the story about a forest ecosystem on the brink of collapse.

Ordinarily, bark beetles are as common as butterflies in a healthy forest. Pines and junipers have evolved with a defense mechanism against harmful insects. They are able to push the bugs out with the pitch they produce.

One walk through the forest and it's easy to see how the trees have been struggling. Tall pines resemble used candle sticks. All along the trunk, the sap dots the bark like globules of melted wax dripping down the side of the tree. But there are simply too many beetles for the trees to fight.

A closer look reveals piles of sawdust-like granules, called frass, clinging to the bark and piling up at the base of the tree. This is the stuff the beetle pushes out as it burrows into the phloem, clogs the flow of nutrients and starves the tree. Covington says these trees have been weakened by overcrowded conditions in the forest and years of drought, and they can't withstand the army of insects chewing away at them.

Before European settlers came to the West, the forests looked and acted differently from how they do today. Ponderosa pine ecosystems were very open with grassy meadows taking up some 70 percent of the forest and perhaps only 20 to 30 trees per acre. The trees grew in clumps and were big with distinctive yellow bark, as many of them were hundreds of years old.

Most of us wouldn't recognize that earlier forest as the ponderosa pine forest we've come to know. Currently, hundreds, even thousands, of small pines fight for survival on a single acre -- choking each other in the battle for sunlight, water, nutrients and survival. The woods have grown dark. Grasses, wildflowers and shrubs have become scarce.

Fire, like the bark beetle, was once an important part of a healthy forest. Both now act as predators. Whereas the bark beetle would break down dead wood and help put nutrients back into the soil, fire would keep dead and dying debris from building up on the forest floor. Its heat was also a necessary signal to some plants to sprout.

Today, we are witnessing how both fire and the bark beetle have the power to destroy hundreds of thousands of acres, the result of more than a hundred years of human-caused changes to the forest including overgrazing of the grasses and fire suppression.

Covington says to save the forests we must start large, landscape-scale restoration which involves thinning out the small trees and allowing fire to burn the way it was intended, along the forest floor, not in the tops of the trees.

"In Arizona, we risk having every acre of ponderosa pine forest degraded by fire, insects or weeds in about 20 years, he says. "We are out of time."

Bonnie Stevens is a contributor to Writers on the Range in Paonia, Colorado (hcn.org). She is an ecologist at Northern Arizona University in Flagstaff, Arizona.

Note: the opinions expressed in this column are those of the writer and do not necessarily reflect those of High Country News, its board or staff. If you'd like to share an opinion piece of your own, please write Betsy Marston at [email protected].

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