Climate change models forecast forest changes

Climate change promises to alter forests in Glacier National Park and wilderness areas in the coming years, but there’s some significant and unpredictable variables that come into play as well.

That was the message presented by Bob Keane, a research ecologist with the Forest Service’s Rocky Mountain Research Station at the Missoula Fire Sciences Laboratory, at a talk sponsored by the Bob Marshall Wilderness Foundation.

Keane began his career studying whitebark pine in the Bob Marshall Wilderness Complex. In recent years, his efforts have focused on climate change modeling and impacts to forests in places like Glacier Park’s Lake McDonald Valley and the Bitterroot Valley south of Missoula.

The modeling comes with a healthy dose of caution, Keane advised — change is constant, never easy or simple, and everything is local. A single mountain, for example, might have several microclimates that preserve a species that a large-scale model might miss.

Having said that, however, the models present some interesting scenarios, particularly in Glacier Park.

One model suggests that western white pine — a once thriving species that has been decimated by blister rust — could once again become the dominant species in the Lake McDonald Valley. The modeling suggests that as the valley gets warmer and drier, white pines could do well because they’re adapted to a more frequent fire regime.

But the model only works if enough of the trees and their offspring survive and become resistant to blister rust. If they don’t, then models suggest western larch could be the dominant species.

Eastern white pine stands are already showing resistance to blister rust. And while the fatal fungus is present in trees in Glacier Park, a host of saplings, particularly in the Apgar area, are surviving below the current canopy of lodgepole pine and larch. Humans could also help by planting blister rust-resistant trees.

Lodgepole pines could end up being the big loser as the Earth warms. While they’re a fire-dependent species, they’re not a fire-resistant species. If fire frequency is too high, lodgepole can’t survive because they can’t survive long enough to reproduce. Other species like subalpine fir also do poorly when fire frequency is high.

There are already signs of significant climate changes, Keane noted — average March temperatures in Bozeman, for example, have increased eight degrees over the last 15 years.

“The shoulder seasons drive everything,” Keane notes.

As springs get warmer sooner, higher elevation snows melt quicker and the landscape dries faster. Fires used to be rare above 6,000 feet because snowpacks melted so late in the year. Now high elevation fires are not uncommon.

Wildfires are also starting earlier in the year, he said, and that harms species like Ponderosa pine. They’re well adapted to fire, but spring fires can kill Ponderosa pines because that’s when they’re growing new tissue. The trees are dormant by fall, which used to be the normal fire season.

Climate change models also suggest a 30 percent increase in lightning, which can ignite fires, and more forest fuels, as higher temperatures create longer growing seasons.

Humans also play a huge role in forest change. For decades, humans tried to suppress wildfires, but historical evidence shows that Native Americans set fires and set them often — 10 to 100 times more land burned in the West prior to European settlement. Historically, wildfires were large but not catastrophic, Keane said.

A healthy fire regime can even be good for fish. Modeling in the Bitterroot National Forest suggests that a frequent fire regime near bull trout streams allows for growth of Douglas fir, which is fire resistant, in riparian areas. When a fire comes through, the Douglas fir survive and shade the streams. A large catastrophic wildfire, however, kills everything.

Another important variable in climate modeling is insects, Keane noted.

“None of the models predicted what mountain pine beetles have done in the past five years,” he said.

Large pine beetle outbreaks have killed millions of acres of trees in the Rocky Mountains, from Alaska to New Mexico.

Keane recommends a more holistic approach for forest management, one that uses fire as a management tool. He noted that a single fire in the Bitterroot cost $50 million to fight.

“For that, we could have restored whitebark pine in a ton of ecosystems,” he said.

The whitebark pine plots Keane examined in the 1990s will get another look in the coming years. The Bob Marshall Wilderness Foundation will host several trips this summer to gather data on those plots. For more information, visit online at www.bmwf.org.