Climate change could force forest changes

In the coming years, Northwest Montana's forests could look far different than they do today, according to a new study co-written by University of Montana professor Steve Running.

The report suggests some forests could be replaced by grasslands while forests now dominated by lodgepole pine could be taken over by other species.

Climate models suggest that the Pacific Northwest as a whole will see an increase in temperature from 2 to 5 degrees Celsius by 2080, with slightly wetter winters and springs, but drier summers.

Heavily influenced by ocean currents, the region has also seen cooler, wetter periods. The last one was from 1946 to 1977. Since then, the climate has been warming as whole.

The greatest increases in temperature are expected in inland British Columbia and Alberta, where the frost-free period is expected to increase by at least a month, and extremely warm summer days are likely to become more common.

Frost-free periods have a dual effect, according to the study. Cold weather kills pests like beetle larvae that feed on trees, and trees begin to grow earlier in the season as temperatures warm.

This can set up disease outbreaks in tree stands. Glacier National Park, for example, has seen outbreaks of spruce budworm and Douglas fir beetle in recent years.

The Douglas fir beetle in particular has killed many old trees in the North Fork region of the Park. The spruce budworm outbreak has infested forests on the east side of the Park. Spruce budworm stunts the growth of tree branches as moth larvae feed on needles. An infested young tree can lose all its needles to spruce budworms. Older trees generally survive but in a weakened state are susceptible to other pests.

Running cautioned that these forest changes won't happen overnight, but changes will likely occur over longer periods of time. For example, a stand of lodgepole growing in the southern reaches of its range in Montana could see a stand replacement fire, but because of climate change, it might be replaced by other tree species like Douglas fir, he noted.

Some areas of the Northwest won't see much change. Forests near the coast are buffered by the ocean's influence, the study noted.

Running collaborated on the study with Richard Waring, of Oregon State University, and Nicholas Coop, of British Columbia. The study looked at 34 different "ecoregions" as far north as the Yukon highlands and as far south as the Sierra Nevada in California.

"We can't predict exactly which tree will die or which one will take its place, but we can see the long-term trends and probabilities," Waring said. "The forests of our future are going to look quite different."