Scientists are studying how beetle-decimated trees may affect rain, temperatures and smog.
By Laura Snider for the Boulder Daily Camera
Wednesday, September 24, 2008
The red-tipped stands of dead pines now crowding the Colorado slopes in the wake of a devastating pine-beetle epidemic may actually be changing the local weather, according to scientists in Boulder.
The National Center for Atmospheric Research has recently launched a four-year project to study how a landscape of dead lodgepole pines could be changing patterns of rainfall, warming surface temperatures and altering the severity of Front Range smog. “Forests help control the atmosphere, and there’s a big difference between a living forest and a dead forest,” said Alex Guenther, who is heading the project for NCAR. Living trees cool the air, both by reflecting the sun’s light and with evaporative cooling.
 A lodgepole pine forest on the eastern slopes of Longs Peak.
And as they transpire water, pulling it through their roots and losing the moisture to the atmosphere, trees humidify the air. Trees are also at the center of complex gas exchanges, absorbing carbon dioxide and letting off oxygen and a host of other volatile organic compounds and particulates into the air. The organic compounds can react to form smog, and the particulates can provide a nucleus for raindrops and clouds to condense around.
When the bulk of a forest dies, as is the case with lodgepoles in the Rockies, these complex interactions shift — and with them, the weather.
“From preliminary modeling and from work in other areas like in the Amazon, for example, where large-scale deforestation has gone on, we know the forest will influence the weather and air quality,” Guenther said. The NCAR project will use airplanes and instruments on the ground to piece together forest-atmosphere interactions from southern Wyoming to northern New Mexico. Though scientists are not exactly sure what they’ll find, they expect to see increased surface temperatures and, possibly, increased smog.
“We expect a forest impacted by pine beetles to have even higher volatile organic compounds, including hydrocarbons, which can play a role in regional air pollution,” Guenther said.
Volatile organic compounds are one of the necessary ingredients needed to form ground-level ozone pollution during hot, summer days. Though the forest’s contribution to ozone is likely small, it could still be a player in places on the Front Range that are out of compliance with air pollution regulations. Foresters predict that all the large-diameter lodgepole pine forests in the Rocky Mountains will be dead in the next three to five years.
Earlier this week, officials reported that pine beetles were moving into urban centers along the Front Range, particularly in Fort Collins. In Boulder, pine beetles have infested three Scotch pines on city-owned land, and foresters reported seeing a couple of dozen other infestations on private land, according to Kathleen Alexander, Boulder’s city forester.
Pine beetles are native to Colorado and have infested pine trees in the city in the past. Urban trees are often healthier and better watered than forest trees, allowing them to be more successful at fighting off the beetles.
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