Report: Trees in trouble in the West

Iconic western forests of lodgepole pine and aspen are in danger of disappearing from some areas in the Rocky Mountain West over the next four decades, if the current rate of warming continues.

That’s the conclusion of a new report — “Rocky Mountain Forests at Risk” — released Wednesday by scientists with the Cambridge, Mass.-based Union of Concerned Scientists and the Louisville, Colo.-based Rocky Mountain Climate Organization.

Among the authors is a University of Montana professor.

The report documents the latest evidence on how warming already is contributing to unprecedented outbreaks of wildfire, insects and drought in forests in Montana, Idaho, Wyoming, Utah, New Mexico and Colorado, a triple whammy that could fundamentally alter the forests if it continues.

Some forests could completely disappear, the report adds.

Projections show marked reductions in areas “climatically suitable” to sustain forests of lodgepole and ponderosa pine and aspen, said Stephen Saunders, president of the Rocky Mountain Climate Organization and co-author of the report.

The projections aren’t ironclad, Saunders said, but still suggest that continued climate change could make the Rockies less suitable for conifer species that currently make up the region’s forests, he said.

“In all cases where you are losing range, is it is too hot and too dry and the species will at least struggle to survive or will not be able to,” Saunders said.

Areas in the Rocky Mountains climatically suitable for lodgepole pine could decline by about 90 percent by 2060 if heat-trapping gases continue increasing at recent rates, based on the U.S. Forest Service projections, the report concludes.

Those Forest Service projections are quantified for the first time in the report.

“The numbers are really beyond startling for me,” Saunders said.

Areas suitable for ponderosa pine to grow could drop by about 80 percent; Engelmann spruce, by 66 percent; and Douglas fir by about 58 percent, the report says.

Forests at risk are defining features of iconic western landscapes such as Glacier and Yellowstone national parks, Saunders said.

The report notes that Yellowstone, Grand Teton, Glacier, and Rocky Mountain national parks attract 11 million visitors each year and generate more than $1 billion annually in visitor spending. Another 60 million people visit the region’s 37 national forests each year.

“If you think of these areas with much reduced forest cover, they would be very different places,” Saunders said.

If the country doesn’t alter its course, those species important to the Rockies are “going to go away,” said co-author Jason Funk of the Union of Concerned Scientists.

The report documents widespread tree mortality across the West that already has occurred.

Aspens abruptly died across large areas of their range in the early 2000s, triggered by an exceptionally hot and dry stretch that peaked in 2002, the report says.

By 2060, areas in the Rockies climatically suitable for aspens could decline by 61 percent and 71 percent in Montana, Saunders said. Montana and Colorado have the most aspens in the West.

Diana Six, a professor of forest entomology/pathology at the University of Montana, said the current outbreak of mountain pine beetles is 10 times larger than any previous outbreak on record. A doubling would have been remarkable, she said.

The most convincing evidence that climate warming is responsible is that the bugs are now surviving in areas where it was once too cold for them to live, such as high-elevation white bark pine forests. The tree is now a candidate for listing as an endangered species.

“It’s now all the way to the Yukon, and that could only have happened with warming,” Six said.

Over the past 15 years, bark beetles have infested 46 million acres, an area nearly the size of Colorado, the report says. The U.S. Forest Service estimates that as many as 100,000 beetle-killed trees now fall to the ground daily in southern Wyoming and northern Colorado alone, the report says.

The region also has seen a 73 percent increase in the number of large wildfires of more than 1,000 acres between 1984 and 2011, an increase of about 18 wildfires a year, Funk said.

On average, wildfires burned more than six times as much land each year from 1987 to 2003 compared to 1970 to 1986, the report says.

Wildfires, infestations and drought are only symptoms of climate change, Funk said. Temperatures have risen, on average, about 2 degrees since 1895.

In the southern Rockies, tree rings are becoming skinnier, indicating less growth resulting from warmer winters and summers, said Park Williams, assistant research professor at Columbia University’s Lamont Doherty Earth Observatory. Warmer temperatures don’t just reduce forest growth, he said. They also enhance forest death, meaning the forests are more susceptible to wildfires and bark beetles.

In the past 30 years, wildfires have burned in 11 percent of the forests in the southwestern Rockies, he said, with wildfires so severe on 6.5 percent that the forests are now dying, Williams said.

In the future, he predicts, large wildfires will open up giant patches in forests that are too large for native tree species to recolonize. Instead, the trees will be replaced by grasses and shrubs, which are better at recolonizing, he said. Forests will survive, he said, most likely in high-elevation stream drainages with more moisture and cooler temperatures.

To respond to the threat, land managers need strategies that can make the forests more resilient, the report says. Carbon emissions also need to be reduced, it says. And it recommends that Congress increase funding for federal land-management agencies.

Reach Tribune Staff Writer Karl Puckett at 406-791-1471, 800-438-6600 or kpuckett@greatfallstribune.com. Twitter: @GFTrib_KPuckett.

At risk

• Quaking aspens have suffered severe and widespread mortality across much of the Rockies due to drought and high temperatures. Continued climate change could eliminate the species from much of its current range.

• Piñon pines have experienced a massive die-off triggered by drought and exceptional heat and will be lost throughout much of its existing range with continued climate change.

• Much of the current range of four other widespread species — lodgepole pine, ponderosa pine, Engelmann spruce, and Douglas fir — is projected to become climatically unsuitable by 2060 if heat-trapping emissions continue to rise.

Source: Union of Concerned Scientists, Rocky Mountain Climate Organization