Mogollon Estates HOA

RAIN CAN HELP CURB BARK BEETLES

Moisture can fortify trees to fight off insect infestations

By Shaun McKinnon
The Arizona Republic Nov. 29, 2003 12:00 AM


If you love trees, pray for rain. Scientists say the estimated 23 million ponderosa and pinyon pine trees that have succumbed to bark beetles in Arizona's forests were so weakened by a prolonged drought that they were unable to fend off the first wave of the tiny bugs.

Whether those bugs return for another helping next year depends on how much moisture the coming winter brings. If the drought persists, the beetles will thrive again, producing an army of trillions. If precipitation levels climb nearer to normal, the added
moisture could fortify trees and keep the bugs from multiplying in such vast numbers.

"One storm, with a couple of inches of rain, seems to have an impact," said Tom DeGomez, a forest-health specialist for the University of Arizona's Cooperative Extension Service in Flagstaff. "We saw that after a storm hit in February and put enough moisture in the ground to help the trees when the beetles came out."

Even if the weather cooperates the beetles' true toll on Arizona's forests may not be clear for years or even decades, scientists say. Aerial surveys of the state's millions of acres of pine trees have already produced a startling portrait of widespread destruction, but those are just the most visible evidence of what could be deeper, permanent losses. "It's still very unclear to us how extensive this potentially could be," said John Anhold, an entomologist and forest-health specialist for the U.S. Forest Service in Flagstaff.

"The beetles have done a number in a lot of the forests that were of poor quality. The (Mogollon) Rim country really got nailed. But now, they have to move out of there into areas that are in better condition," he said. "It's taking morebeetles to overcome these healthier trees."

Foresters believe their current damage estimate of 23 million dead pine trees is conservative; the toll is expected to rise when aerial surveys are fully analyzed in a few weeks. Those numbers could grow next year when additional surveys are conducted. That's what happened between last year and this year. The aerial tours wrapped up last August, but the beetle hordes continued to spread into the fall. As a result, the 2002 counts were too low and the 2003 counts include trees lost the previous year. In all, beetles infested more acres of trees during those two years than were burned by wildfires, even accounting for the calamitous "Rodeo-Chediski" blaze.

The latest surveys indicate the infestation spread fastest in the Kaibab National Forest in Northern Arizona and the Tonto National Forest northeast of Phoenix. At the end of 2002's survey, 49,125 ponderosa pines in the Kaibab were dead; the 2003 survey counted 1,063,706. In the Tonto, the toll rose from 495,810 dead trees to 8,157,970 at the start of this autumn. Losses were equally grim in and around Prescott, where more than 4.1 million trees have succumbed, and on the San Carlos and Fort Apache reservations, where the damage covers nearly 200,000 acres of eastern Arizona.

The dead trees pose a fire danger, though not, significantly higher because the forests overall are so dry. "This summer, lightning would hit a tree attacked by bark beetles, and it wasn’t exploding or taking off any differently than normal trees,” said Gary Roberts, fire-prevention officer for the Tonto forest's Payson district. "But give it a couple more years, and they will become much more volatile."

Most of the trees will remain standing for a few years, said DeGomez, of the University of Arizona. Their needles will fall first, then their twigs and, in four or five years, the trees themselves will begin to topple, weaving a carpet of dry, dead wood that will spread flames faster than typical groundcover.

Prolonged drought jump-started the current bug attack, weakening the ponderosa and pinyon pines so much that they were unable to defend themselves. Most experts agree it was a confluence of events - what DeGomez describes as a "perfect storm" – that allowed the invasion to spiral.

"The bark beetle has always been around as a natural thinning agent for forests,” Roberts said, "but the forests are too dense, too thick." A century ago, 20 to 40 pine trees filled each acre in Arizona's forests, compared with 160 to 1,000 or more today, which increases the competition for water and other resources. A drought now is much more stressful on trees than it would have been 50 years ago, Roberts said. "If we don't thin them out, those forests will burn to the ground," he said. "One way or another, nature is going to set things in balance. If we've interrupted things, it's going to be doing it on its terms rather than ours."

Although scientists have never been able to study the effects of a beetle infestation on wildfires, it's clear that the bugs are creating fuel sources, said Wally Covington, director of the Ecological Restoration Institute at Northern Arizona University. Some of the worst fires that swept forests around San Bernardino, Calif., last month occurred in areas also hit hard by bark beetles.
"Those were huge blowups," Covington said. "Fires that do occur in beetle stands are going to be extremely severe. We've dodged a bullet so far. But there will definitely be fires."

Over the long term, the beetle attacks could alter local ecosystems by allowing invasive plant species to gain a foothold, Covington said. If the drought persists and the forests remain dense, beetles will continue to wipe out huge swaths, until little remains of the state's population of pine trees. "Clearly, this is a crisis," he, said. "We are absolutely dependent on the high country in Arizona, for water, for biological diversity, for human habitat. We've got to think big and act big."

FACT ABOUT BARK BEETLES

What you should know about the infestation in Arizona:

Q: Where did all these bark beetles come from?
A: Pine bark beetles are as common as butterflies in a healthy forest, according to Wally Covington, director of the Ecological Restoration Institute at Northern Arizona University. Ordinarily, trees repel attacks by producing pitch or sap, which keeps beetle eggs from hatching and keeps the adult insects from burrowing more deeply. Prolonged drought and poor conditions in Arizona's forests have overstressed trees, leaving them vulnerable to infestation. Many trees simply can't defend themselves anymore.

Q: What trees are affected most?
A: Ponderosa and pinyon pine trees are most often attacked.

Q: How many trees have been infected?
A: It's hard to tell, but aerial surveys suggest the number could exceed 23 million across Arizona's forests. Bark beetles have destroyed more acres of trees than wildfires during the past two years.

Q: Will the dead trees increase wildfire danger?
A: Yes. The dry treetops can aid the spread "crown fires," an especially destructive form of wildfire that burns hot and destroys quickly. Once the needles and the trees themselves fall, the risk of ground fire will climb and the heavy amounts of fuel could help feed crown fires in the remaining trees.

Q: How many bark beetles are in the forests?
A: Impossible to tell. Scientists were estimating an infestation in the trillions in 2002. One tree can be infested by hundreds even thousands of beetles at once.

Q: What happens to an infested tree?
A: The beetles burrow in through the outer bark to lay eggs. When those eggs hatch, the new beetles chew away at the tree's inner bark, choking off the flow of moisture and nutrients to the rest of the tree. Needles change color from dark green to a rust red before falling off. When the new beetles are mature enough, they fly off to another tree and start the process over again.

Q: How do bark beetles find weakened trees?
A: Beetles can detect a volatile compound emitted by stressed pine trees, according to the University of Arizona Cooperative Extension Service. The insects then give off a pheromone to attract other beetles.

Q: Is it possible to spray for beetles?
A: No pesticides have proved effective to beetles once they have attacked a tree, according to the extension service. Several pesticides prevent attacks, but forest-wide spraying is impractical and far too costly.

Q: What else can be done?
A: Reducing the number of trees in a given area allows those remain to grow stronger, according to the university extension service. If you own land with trees that have not been infected, contact a professional arborist about thinning the area. If the area has infected trees, get rid of them quickly.

Q: What happens to the trees that have been attacked?
A: Most of them die. If they're not removed, they will fall eventually.

Q: Will the hardest-hit forests recover?
A: Some of them will, but it could take decades or even a century or more. In forests with the heaviest infestation, entire stands of trees could be lost, forever altering the local ecosystem, scientists say.