Bark beetles survived cold snap
Vail, CO Colorado
GLENWOOD SPRINGS ” Below-zero weather earlier this month was not enough to wipe out bark beetles that have killed millions of trees in the mountains.
“On a local scale it might affect small populations, but the temperatures haven’t lasted long enough,” said Cary Green, timber management assistant for the White River National Forest in Minturn.
Beetles are attacking spruce and lodgepole pine and leaving thousands of acres of dead trees.
“In 2006, bark beetles infested 750,000 acres of Colorado forests,” said White River spokeswoman Sally Spaulding. “The beetles are operating at an incredible pace and scale and there’s not much we can do to stop them.”
Deep, bone-chilling cold, sustained over a long enough period, can kill the bugs, which bore underneath the bark, lay their eggs and deposit the fungus that actually kills the trees.
“It really takes three or four days to a week of temperatures colder than -35 degrees,” to kill bark beetles, said Joe Duda, forest management division supervisor with the Colorado State Forest Service in Fort Collins.
Bark beetles have a built-in protection against the cold. They produce a kind of antifreeze called glycerol that prevents them from freezing.
“It has to be cold enough to overcome their system,” Duda said.
Even then, some populations will survive. Beetles on part of a tree “below the snowline don’t get cold because of the insulating” effect of the snow, Duda said.
“Our last cold snap three weeks ago didn’t last long enough,” Green said. Temperatures got down to 25 below zero at one point in late January but rose to 5 below within a few days. And those were nighttime temperatures.
“It was in the high teens and 20s during the day,” Green said.
Winters just aren’t as cold as they used to be.
“Temperatures have warmed (over time),” Duda said. “Weather statistics show it’s not so much the high temperatures increasing but the normal cold temperatures are not getting as cold.”
Duda said he’s seen beetle infestations in lodgepole pines growing above 10,000 feet in elevation, where historically the temperatures were cold enough to keep them at bay and the growing season was shorter. Warmer winter temperatures have made those high altitudes more hospitable to beetles.
Some of the lowest historical temperatures in the state were in the Eagle area in the 1950s, Green said. The National Weather Service Web site reports a low of -51 degrees in January 1954 at Eagle.
“Winters (then) were pretty harsh with sustained temperatures for a long time,” Green said.
Warming winter temperatures are the least of it. Sustained drought and stands of mature, large-diameter lodgepole and spruce trees have created the perfect conditions for beetle infestations, Green said.
In Summit and Eagle counties there is “80 to 90 percent mortality,” he said. With nothing to stop them, the beetles could kill 90 percent of the lodgepole trees in central Colorado.
Local, state and federal land management agencies formed the Northern Colorado Bark Beetle Cooperative last year to tackle the problem.
“We agreed the issue is bigger than any of us,” said Don Carroll, former deputy supervisor of the White River National Forest who now heads up the project.