"In recent years some researchers have thought the pine beetle outbreak in the Southern Rocky Mountains might have started in one place and spread from there," said Chapman.
"What we found was that the mountain pine beetle outbreak originated in many locations. The idea that the outbreak spread from multiple places, then coalesced and continued spreading, really highlights the importance of the broad-scale drivers of the pine beetle epidemic, like climate and drought."
Mountain pine beetles range from Canada to Mexico and are found at elevations from sea level to 11,000 feet. These native insects have shaped the forests of North America for thousands of years by attacking old or weakened trees, resulting in younger forests.
The effects of pine beetle overpopulation are especially evident in recent years on Colorado's Western Slope, including Rocky Mountain National Park, with a particularly severe epidemic occurring in Grand and Routt counties.
The most recent mountain pine beetle outbreak began in the 1990s, primarily in scattered groups of lodgepole pines at low elevations in areas of lower annual precipitation.
Following the 2001-2002 drought, the outbreak was "uncoupled" from the initial weather and landscape conditions, triggering a rise in beetle populations on the Western Slope and propelling the insects over the Continental Divide into the Northern Front Range to infect ponderosa pine, Chapman said.
The current pine beetle epidemic in the Southern Rocky Mountains also was influenced by extensive forest fires that ravaged Colorado's Western Slope from roughly 1850 to 1890.
Lodgepole pine stands completely burned off by the fires were followed by huge swaths of seedling lodgepoles that eventually grew side-by-side into dense mature stands, making them easier targets for the pine beetles.
|Contact: Cheryl Dybas|
National Science Foundation