Scientists with the National Center for Atmospheric Research in Boulder, Colo., recently began a four-year study aimed at determining whether the massive tree mortalities triggered by bark beetles have altered temperatures and rainfall patterns. More importantly, the research aims to understand whether the destruction is accelerating global climate change and increasing levels of ground-level ozone pollution.
The outcome of the study could have far-reaching impacts on how water resources and forests are managed, as well as shape policies dealing with air-quality issues such as climate change. It could also accelerate research into cutting-edge technologies designed to fight the damaging bark beetle infestations.
The study, which includes researchers from universities across the United States, Europe and Japan, will be limited to atmospheric impacts in the three states -- Wyoming, Colorado and northern New Mexico -- where the beetle infestation is most intense.
One of the project's goals is to establish a multidisciplinary network of other scientists in an effort to expand the research to look at the effects of losing trees not only to beetles but development and other landscape changes across the world.
"Forests help control the atmosphere, and there's a big difference between the impacts of a living forest and a dead forest," said Alex Guenther, an earth systems scientist with the National Center for Atmospheric Research who is leading the study.
For example, researchers know that trees cool the air when they evaporate moisture through their leaves -- a process called transpiration. They also absorb, and reflect, heat from the sun. Disrupting these basic functions and temperatures in a region that has suffered large-scale tree mortalities can spike as much as 4 degrees Fahrenheit, according to initial computer modeling cited by the National Center for Atmospheric Research.
Guenther and others suspect that altering these natural processes, even in subtle ways, could reduce rainfall amounts in the arid western United States by disrupting the interaction between tiny airborne particles from plants that rise up into the atmosphere and seed clouds with water droplets. These changes to rainfall patterns could last for decades and cause water shortages.
"Here in the western United States, it is particularly important to understand these subtle impacts on precipitation," Guenther said.
In the study, researchers plan to use specially equipped aircraft and observation towers 100 feet tall to measure emissions above the tree canopy, as well as soil and moisture sensors on the ground.
Guenther said he and the other scientists participating in the project fully expect to find that temperatures have increased and rainfall amounts decreased within the three-state study area due to the mass destruction of trees. He notes that computer models in the Amazon rainforest, which has undergone extensive deforestation, indicate temperature increases are occurring there.
But the issue is an extremely complicated one, Guenther concedes.
"We may end up with more questions than answers," he said.
While the researchers have a lot of questions they want to answer, one thing is already clear: The bark beetles have left a swath of destruction, leaving behind a vast expanse of rotting tree trunks that increase the threat of devastating wildfires.
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| Mountain pine beetle damage. Photo courtesy of BLM. |
The bark-beetle infestations have had an especially devastating impact on some of the country's most prized national forests.
In the Yellowstone and Grand Teton national parks in Wyoming, bark beetles have killed millions of pine trees. At the Dixie National Forest in Utah, the beetles have infested more than 450,000 acres and destroyed nearly half the state's population of mature spruce pines. The U.S. Forest Service estimates that in the next five years virtually all the mature lodgepole pines will have disappeared from the Medicine Bow-Routt National Forest on the Colorado-Wyoming border.
Colleen Keyes, forest-health program manager for the Utah Division of Forestry, Fire and State Lands, said there are vast sections of Cedar Canyon in the Dixie National Forest in southwest Utah where the dead trees stretch out as far as the eye can see.
"The impact of seeing that is more than I can describe," Keyes said.
At barely a quarter-inch in length, the mountain pine beetle doesn't look very menacing. But it is nothing less than the Grim Reaper to lodgepole, ponderosa, sugar and western pine trees.
The National Center for Atmospheric Research study is focusing on the mountain pine beetle because it has caused the most damage. That is due mostly to the fact that unlike other bark beetles, which limit their attacks to one specific species of pine, the mountain pine beetle indiscriminately attacks almost any pine species.
"Throughout history we've seen an awful lot of tree mortality credited to that insect," said Roy Mask, a Forest Service entomologist in Gunnison, Colo. "They are the most significant mortality agent of pines."
Mountain pine beetles do most of their damage when the female beetle bores holes and digs "egg galleries" where beetle larvae hatch. The beetles also bore into trees to eat the moist inner bark. All this digging hampers the tree's ability to nourish itself because the bark stores and transports water and nutrients between the leaves and the roots.
Further complicating matters is the fact that as the beetles carve into the trees they introduce blue-stain fungi that also interfere with the water and nutrient transport system, according to research by the University of Arizona.
Perhaps most alarming, the mountain pine beetles are spreading rapidly, entomologists say, aided by an already warming climate that allows them to survive the harsh winters that have traditionally slowed their march across forests. Today, the beetle is found from the Pacific Coast east to the Black Hills of South Dakota, and from northern British Columbia to northwestern Mexico.
As a result, Forest Service officials estimate that potentially millions of acres of pine trees will die over the next five years.
A major focus of the research project will be to determine how the inevitable forest fires aided by the presence of millions of dry, dead trees affect regional air quality.
When a pine tree is ravaged by bark beetles and begins to die, the pine needles turn red and are brittle and dry. Eventually, all that is left is a dead stump pockmarked by hundreds of tiny boreholes. These trees eventually fall to the ground.
The brittle pine needles and the dead trees create an extreme fire hazard, foresters say.
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| This picture of a Colorado forest depicts the contrast between healthy trees and those that have suffered damage due to the beetle infestation. Photo by Eryn Gable. |
In addition to the danger forest fires pose to both people and wildlife, they can negatively affect air quality. That is because forest fires can release into the atmosphere millions of tons of carbon dioxide -- the chief man-made contributor to global warming -- as well as tiny particles that can damage the lungs.
The scientists participating in the study want to know how much this carbon affects the climate. Mark Wenzler, the clean air program director for the National Parks Conservation Association, is already convinced that any increase in wildfire activity would create "a huge problem from an air-quality perspective."
There is lots of evidence to suggest that bark-beetle infestations cause wildfires. A series of devastating forest fires at Yellowstone National Park in 1988 was preceded by a massive bark beetle infestation that left millions of dead trees to burn, said Steve Munson, a Forest Service entomologist in Ogden, Utah.
"When you build up the forest fuels that can feed a fire, it can be devastating," Munson said. "With large fuel loads like that, once they start to burn, it's difficult to get on top of it."
No one doubts that there are many more dead trees on forest floors today than there were even five years ago.
The National Wildlife Federation this summer warned of the risk of wildfires in the western United States due to the volume of dead trees. And Congress last month approved a $600 billion continuing resolution package (E&E Daily, Sept. 29) that includes about $125 million to reduce the number of dead trees in the West that could help fuel wildfires.
At Medicine Bow-Routt National Forest, where an estimated 450,000 acres of trees have been infected by the mountain pine beetle, the many thousands of trees that are dying or are already dead are a forest fire waiting to happen, said Tony Tezak, the forest fire management officer at Medicine Bow-Routt.
"If we get a hot, dry summer, we could potentially have a real problem," Tezak said. "And we know we'll have a hot, dry summer at some point. It's not really a question of if, but when."
The trees don't have to burn to accelerate the impacts of global warming.
While living forests act as "carbon sinks" removing huge volumes of carbon dioxide from the atmosphere each year, dead trees lose this ability to photosynthesize.
What's more, as trees die, they release back into the atmosphere the carbon they had sequestered over the years to grow new leaves and repair tissue.
Guenther said this could be a significant -- and largely unrecognized -- source of greenhouse gas emissions.
The National Center for Atmospheric Research study will also explore whether bark beetle infestations exacerbate ground-level ozone pollution.
Ozone -- the biggest air-pollution problem in the United States -- is the result of a chemical process in which pollution, mostly from cars and factories, mixes in the sunlight and heat.
But trees also play an important role, emitting volatile organic compounds that are necessary for ozone to form. Scientists believe that when trees are attacked, they release more of these hydrocarbons and particles into the air.
The good news is that most forests are far from urban areas, in places where the increased emissions of hydrocarbons from trees cannot mix with pollution from cars and factories to form ozone. However, some cities in the Rocky Mountain region, particularly Denver, are close enough to forests that these emissions could impede their ability to comply with federal ozone standards, Guenther said.
In addition, as pines are destroyed by beetles, they are replaced by species like aspen, which Guenther said emit more of the hydrocarbons that help form ozone.
If the destruction caused by bark beetles plays a major role in air quality, stopping them might become more critical, but it won't be easy.
Scientists have been studying how to stop or slow bark beetle infestations for decades, without much success.
Currently, Forest Service scientists are working to develop a pheromone chemical that can signal other beetles to leave the area.
When a beetle finds a suitable tree in which to burrow, it sends out a pheromone to attract other beetles to the tree to help it overwhelm the tree's natural defense system. Conversely, when things get too crowded, the beetles release a different pheromone that repels any new insects from burrowing into the tree, said Harold Thistle, a Forest Service engineer in Morgantown, W.Va., who is working to develop the strategy.
Thistle and other scientists have experimented with various pheromones, with mixed results. Thistle is recruiting other scientists to work with him to refine the technology, with the goal of developing a chemical that can be applied over a wide area of landscape.
"This is greener than cutting down infected trees or using chemical insecticides," Thistle said.
Even if the pheromones work, however, most forest managers agree that the best solution is prevention, and that can best be done by properly managing the forests. This means that when the Forest Service replants trees in damaged areas, it should plant diverse species instead of thick stands of pines that allow beetle infestations to be so destructive. It also means thinning areas by using controlled burns.
The Forest Service is developing long-range vegetation management plans that would incorporate many of these principles in an effort to mitigate bark-beetle problems, said Munson, the Forest Service entomologist in Utah.
"Suppressing fire has allowed these trees to grow older and thicker, which is perfect for the beetles," he said. "The insects we see today are just taking advantage of what we're offering to them."
Scott Streater is a freelance journalist based in Colorado Springs, Colo.
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