Aspen symposium: Grim outlook for forests because of bugs, disease
Ryan Summerlin February 19, 2011
ASPEN – The outlook for forests in western North America is grim: White pines in majestic Yellowstone National Park face obliteration; two-thirds of aspen forests, including many in the Roaring Fork Valley, are likely doomed; and bark beetle infestations will intensify with climate change.
The grim outlook was delivered Friday by scientists at the “Forests at Risk” conference in Aspen. More than 400 conservationists, U.S. Forest Service workers and curious folks attended the conference presented by For the Forests, an Aspen nonprofit.
“There wasn’t much good news in anything any of you had to say,” moderator Renee Montagne of National Public Radio told a panel featuring the first four presenters at the conference.
Tom Swetnam, professor and director of the laboratory of tree-ring research at the University of Arizona, said climate change will exacerbate the drought cycles that the study of tree rings show have regularly occurred in North America. There might be more rainfall as a result of climate change, he said, but it will be more than offset by higher temperatures.
That will create problems for virtually all species of trees in western forests. Jim Worrall, a plant pathologist with the U.S. Forest Service and a top expert on Sudden Aspen Decline (SAD), said there is “overwhelming circumstantial evidence” that the problem is tied to climate change. The drought that peaked in Colorado and much of the West in 2002 stressed trees and made them more susceptible to bugs and diseases. SAD mortality in aspen trees peaked in 2008 when 542,000 acres of the iconic tree died off.
There are about 16 million acres in the western U.S. where conditions are suitable for aspen trees, Worrall said. By 2060, about 11 million acres will likely be lost.
He showed a map that showed the Roaring Fork Valley surrounded by good habitat for aspens. By 2060, if current trends continue, only the highest elevations, like up Independence Pass, will remain suitable, another map indicated.
Between 2003 and 2009, about 1.1 million acres of aspen forests died off. SAD is “beginning to fulfill projections,” Worrall said.
As climate change brings higher temperatures and dries out the earth for longer periods of time, more aspens will be susceptible to SAD, according to Worrall. Droughts, like what hit in 2002-03, will stress the trees and SAD will hit in “spurts,” he said.
Aspens won’t be totally wiped out because of their adaptability. “It seems certain we’ll have aspen somewhere in the landscape far into the future,” Worrall concluded.
The same cannot be said for white pine, which dominate the forests in Montana and parts of Wyoming. Diana Six, professor of forest entomology and pathology at the University of Montana, said mountain pine beetles have marched farther north as temperatures have increased. Places like Yellowstone that were previously protected by cold temperatures that kept bugs at bay are now susceptible to the mountain pine beetle outbreak. White pines have no defenses; Six witnessed large stands getting wiped out in just three years.
“We don’t believe these trees are going to be coming back,” Six said.
Increasing mortality isn’t limited to white pine and aspen. Phillip van Mantgem, research ecologist with the U.S. Geological Survey, is part of a team that has monitored 76 old-growth forest stands throughout the western U.S. for 20 years. The research is so detailed they tracked the health of individual trees.
The results show 87 percent of the stands have increasing mortality rates, and the mortality rate doubled over the last 18 years.
“The ultimate cause behind it is probably warming,” van Mantgem said.
Montagne asked the panel if anything can be done to “fix” the problem with the forests, which have been devastated by bark beetle epidemics over the last decade.
The beetle infestation affected 400,000 acres in Colorado and southern Wyoming last summer, an aerial survey by the Forest Service and Colorado State Forest Service showed. The infestation has spread to about 4 million acres covered in lodgepole pine, five-needle pine and Ponderosa pine trees since the outbreak began in 1996, the agencies say.
Trees have been killed on 500,000 of the 2.3 million acres of the White River National Forest, which includes public lands around Aspen.
Swetnam said public land managers can’t concentrate on restoring forests to a past condition. The changes have been too drastic. The focus should be getting forests into conditions where they can be resilient over time. That will require use of prescribed fire. Firefighting has been eliminated as part of “the Smokey Bear effect,” he said, referring to the Forest Service firefighting.
“We need to reintroduce fire,” Swetnam said, stressing that “we can’t just rely on chainsaws.”
“It’s a huge, huge challenge there because of the smoke [risk] and escaped fire and so on,” Swetnam continued. “Fire will happen, regardless, it’s just a question if it’s on our terms.”