Forest's death brings higher temps, researchers suspect

 21 October 2009

Forests of dead beetle-kill could be speeding regional climate change, increasing temperatures and decreasing rainfalls across the American West.

By Scott Streater
For the Daily Climate

The drive along State Highway 230 into southern Wyoming offers a startling view: A forest of dead or dying lodgepole pines stretching miles across the Medicine Bow-Routt National Forest.

"It's just a sea of red needles or gray, skeletal trees," said Tony Tezak, the forest fire management officer at the national forest that straddles the Colorado-Wyoming border. "The scope of the devastation is pretty staggering. It's pretty shocking to see."

Tezak has watched in horror the past three years as mountain pine beetles have infested an estimated 900,000 acres of lodgepole pines in the forest. "The threat shows no signs of abating," he said. The infestation turns the pine needles brittle and leaves the dead trees pockmarked with hundreds of tiny boreholes where the beetles tunneled in to lay eggs and eat the moist inner bark. Tezak estimates more than a third of the national forest's 3 million trees could be dead by the time the current outbreak subsides.

But there might be a more consequential impact to the carnage: The beetle kill could be accelerating regional climate change by increasing temperatures and decreasing rainfalls in Colorado, Wyoming and northern New Mexico.

"The local impacts where the forest has been destroyed will be fairly dramatic," said Peter Harley, an associate scientist at the National Center for Atmospheric Research in Boulder, Colo. "The big question is how much of an impact will this have?"

NCAR researchers are about a year into a four-year study to gauge and assess such effects.

The research centers in large part on the ability of living trees to cool the air when they evaporate moisture through their leaves – a process called transpiration – and what happens to climate conditions when large numbers of trees die. Trees also help control surface temperatures by absorbing and reflecting heat from the sun.

Disrupting these basic functions by destroying wide swaths of trees across the West appears to spike surface temperatures. Already the researchers have completed computer modeling studies indicating that if the millions of acres of pine trees in Colorado were to die, that could raise temperatures statewide nearly 4 degrees Fahrenheit, said Christine Wiedinmyer, a NCAR scientist in Boulder and, with Harley, one of the principal investigators on the project.

"It's still highly uncertain. People have not gone out and measured the impacts of dead forests," Wiedinmyer said. "But it looks like it can change the temperatures on the ground."

NCAR researchers believe these disruptions could reduce rainfall amounts in the arid West by severing the interaction between tiny airborne particles from plants that rise up into the atmosphere and seed clouds with water droplets, possibly decreasing the availability of particles to form clouds.

A four-degree temperature rise in the West could be particularly calamitous to a region already feeling the stress of limited water supplies. A study by the U.S. Global Change Research Program released earlier this year found the drought, wildfire and invasive species invasions accompanying rising temperatures will reshape the landscape, threatening the region's biodiversity, water supplies, and agriculture and tourism industries. "The most likely future for the Southwest is a substantially drier one," the report's authors noted. "The combined effects of natural climate variability and
human-induced climate change could turn out to be a devastating 'one-two punch' for the region."

To assess whether massive tree mortalities accelerate global warming on a region-wide scale, scientists are using specially equipped aircraft and observation towers 100 feet tall to measure water and carbon emissions above the tree canopy in three areas: One where a beetle infestation is in the beginning stages, one in the middle of an outbreak, and one where a beetle attack has already taken place and the trees are dead. They're also measuring whether the loss of the trees has impacted temperatures and rainfall patterns.

Various bark beetle species have left behind a huge swath of destruction across the West, impacting some of the country's greatest parks, including Yellowstone and Grand Teton national parks, where beetles have killed millions of pine trees.

NCAR researchers are focusing on the mountain pine beetles because unlike other bark beetles that target specific pine species, the mountain pine beetle will attack almost any pine.
Mountain pine beetles alone have killed lodgepole, ponderosa, and other western pines on an estimated 10.1 million acres across a 12-state region from New Mexico to North Dakota since the latest outbreak began in 2003, according to the Forest Service's National Insect and Disease Survey database.

Overall, mountain pine beetles and the other species of bark beetles have killed trees over a staggering 24.8 million acres in the interior west, mostly in the Rocky Mountain region, according to the Forest Service data provided by the Forest Health Technology Enterprise Team in Fort Collins, Colo.

"This is a landscape-altering event, there's no doubt about it," said Steve Munson, a Forest Service entomologist in Ogden, Utah.

Rotting tree trunks left behind are a wildfire threat, said Tezak, the forest fire management officer at Medicine Bow-Routt. Wildfires wiped out 5.3 million acres of forestland nationwide last year, and have already burned more than 5 million acres this year.

Part of the NCAR study includes examining the air-quality impacts as a result of tree mortalities due to wildfires.
If the NCAR research finds compelling evidence that massive tree mortalities are impacting temperature and rainfall patterns, it could prompt changes to forest management policies that better adapt to an altered climate.

For example, instead of replacing the dead pines by replanting more pines, which eventually would become targets of future beetle outbreaks, forest managers should diversify tree species by planting spruces and ash trees, Munson said.

"Right now we have campgrounds that are 100 percent lodgepole pine, and they're disappearing," he said. "We need to do something different. "We need to think long term and develop strategies for how to keep them vegetated and reduce susceptibility to bark beetles."

Scott Streater is an environmental journalist who lives in Colorado Springs, Colo.

Photos (top to bottom): Pine forests are dying throughout the Rocky Mountains (©Carlye Calvin/NCAR); mountain pine beetle - Dendroctonus ponderosae (Courtesy U.S. Forest Service and University of Arizona); NCAR scientist Alex Guenther examines an instrument at a Colorado field site (©Carlye Calvin/NCAR); a tower rises above the forest to allow scientists to explore the exchange of gases and particles between forest and atmosphere (©Carlye Calvin/NCAR)

Story © Scott Streater. All rights reserved.

Contact Daily Climate editor Douglas Fischer at dfischer@dailyclimate.org

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