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Monday, October 7, 2002

The bark beetle infestation has affected large numbers of trees in and around the Los Alamos area and nearby communities as shown in this photo of Pueblo Canyon looking east toward Santa Fe. Photo by LeRoy N. Sanchez, Public Affairs

Recent rains welcome, not enough to stem drought in region

Despite recent rains and predictions for a wetter than normal winter, the drought is deepening and intensifying across the southwest, according to Laboratory ecologists.

"We're in the middle of a long-term drought," said Diana Webb of the Risk Reduction and Environmental Stewardship (RRES) Division and chair of the Interagency Wildfire Management Team. "We are experiencing a natural phenomenon. Unfortunately, our forests are not healthy. The trees are overcrowded, stressed and weak from lack of moisture in recent years. Healthy trees can fight back against insects or disease, but drought-stressed trees are susceptible to many types of problems," she said.

Long-term forest health problems such as infestation with various bark beetles are not likely to be mitigated by current weather conditions. "Typically we get about 19 inches of precipitation a year," said forest ecologist Randy Balice of Ecology (RRES-ECO). "During the past 12 months, we've only had about 50 percent of that."

Balice said the current climate outlook for the region indicates that precipitation will be slightly above normal this winter. The additional precipitation "may not be enough to significantly alter high fire conditions and the drought-caused mortality," Balice said. "It may not be enough moisture to revive the trees."

Another factor, said Balice, is that temperatures the past 12 months have been about 4 percent above normal, adding that a forecast of normal temperatures and a minimal increase in moisture could lead to another extreme fire season and continued tree mortality in 2003.

Severe drought also has radically increased bark beetle activity in Northern New Mexico (see accompanying fact sheet). "Beetles are attracted to stressed and dying trees," said insect ecologist Tim Haarmann, also of RRES-ECO. "They've been known to fly up to two miles to reach an intended host tree. However, once beetles have invaded an area and populations reach epidemic levels, there are often enough beetles to overcome and kill even healthy trees. The bark beetle infestation we are currently experiencing is nature at work."

Trees aren't dying in the area because of forest fires of the past few years. "Certainly the drought, coupled with overcrowded conditions, is the significant factor contributing to the infestation, which is a regional problem occurring far from the Cerro Grande Fire area and from where tree thinning is taking place," said Carey Bare, RRES-ECO natural resources team leader. "Future tree mortality is very difficult to estimate and is highly dependent on the length and severity of the drought. Some estimates range as high as 90 percent for some species in some areas," Bare said.

"We are emphasizing certain aspects of our thinning prescriptions as a result of the beetle infestation, although fire hazard is still the main consideration in prioritizing areas to be thinned," Bare said. "Forests are being treated on an area-by-area basis with all factors considered in removing trees at that time."

Bare said the Laboratory is emphasizing removing dead, dying and potentially hazardous trees while leaving larger, still-healthy ones. Adequate numbers of small trees with greater resistance to the beetle are being retained. Slash and logs are being removed from the thinning areas in as short a time as is practical, he said, adding that during the winter months the Lab plans to re-enter areas already thinned in order to remove additional dead and dying trees.

Bare added that changes in forest conditions also are affecting wildlife on Lab property. He said the Lab is monitoring animal migration and behavior to better manage their natural habitat. "Through planned thinning and by leaving some of the dead trees behind, we can provide important cover or homes for many wildlife species, from mammals to birds and insects," he said.

"For now, and for the next few years, we can expect to see dead and dying trees throughout the Pajarito Plateau," Webb said. "We have close ties to our forests, and watching this process will be hard. However, there is little we can do to reverse this; once the trees start to turn brown, they cannot be brought back. While these changes may be visually disturbing to us now, we need to remember that this is nature's way of thinning our forests and that the long-term result will be a healthier forest in the future."

According to the National Drought Mitigation Center, regional drought conditions in Northern New Mexico and southern Colorado remain "exceptional" or "most extreme." Weekly updates may be found on the U.S. Drought Monitor Web site at http://www.drought.unl.edu/dm/monitor.html online.

For more information, contact Balice, Haarmann or Bare at 7-0730.

Bark beetle fact sheet

There are two primary beetles infesting Northern New Mexico trees. Piñon ips, Ips confuses, is currently attacking piñon pine trees. The mountain pine beetle, Dendroctonus ponderosae, infests ponderosa pine. This fact sheet, generalized for the two beetles, was prepared by Tim Haarmann and Carey Bare of RRES-ECO, and Deanna Williams of the U.S. Forest Service. For more information, go to the U.S. Forest Service Web site at http://www.na.fs.fed.us/spfo/pubs/fidlpage.htm online.

  1. Beetles spend their entire life under the bark of infested trees except for a few days during the summer when adults emerge and fly to new trees.
  2. Usually during late summer and early fall female beetles construct egg galleries under the bark, mostly in the phloem, or inner bark, of newly infested trees. Sometimes, eggs are laid in late spring by females that survived the winter. Surviving females may either re-emerge and again attack trees or merely extend their egg galleries.
  3. Beetles usually require one year to complete a life cycle. At high elevations where summer temperatures are cool, two years may be required to complete the life cycle. However, during unusually warm years several generations can be completed in one year.
  4. The beetles have already completed their flight for this year. Look for boring dust or pitch tubes to identify newly infested trees (Fig 1-3).
  5. Unseasonably low temperatures may slow outbreaks. It is not certain how long these temperatures need to be maintained before most beetle larvae are killed.
  6. Unfortunately, beetles may still survive on warmer slopes and reinfest areas in a few years. In addition, beetles in thick-barked trees and in portions of tree trunks that are below the snow line are protected from the cold and are more likely to survive.
  7. A cold winter with little snowfall may slow the outbreak but would probably need to occur for several years. Food supply is generally the most limiting factor that returns beetle populations to endemic levels.
  8. A wet winter may reduce the stress that some trees are under, allowing them to effectively "pitch out" invading beetles (Fig. 4). However, even a healthy tree cannot effectively fight off a mass attack once beetle populations reach epidemic levels. A wet winter is unlikely to kill larvae unless temperatures drop below those mentioned previously.
  9. Large diameter trees with thick phloem are often first to be attacked, but as beetle populations increase and preferred food sources become scarce, they will begin to infest smaller diameter trees.
  10. The best case scenario is that with relief from the drought, beetles may be prevented from infesting some areas. However, food supply is the most limiting factor for beetle populations once they reach epidemic levels. Forestry practices may be able to help in some situations but if they are not applied with extreme care they may actually exacerbate the problem by producing more beetle food in the form of green slash left after logging and trees stressed and damaged by logging equipment.
  11. Homeowners may be able to save individual trees by watering and fertilizing. Contact the Cooperative Extension Office in Los Alamos at 662-2656 for more information about applying insecticides to certain high-value trees. Specific guidelines are available for recommended homeowner and forestry practices.
  12. The worst case scenario is that the drought will continue and with beetle populations at epidemic levels, almost all mature piñon and ponderosa pine trees will be infested. There is no clear model for predicting rate of spread. It is known that thousands and even millions of acres of trees have died from bark beetle outbreaks.
  13. At the Laboratory, trees with visible evidence of bark beetle are being cut and, rather than being distributed to the public, are disposed of in burn units.
  14. Bark beetles look similar to the common observer.

-- Fran Talley

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