Forests face more fire, insects and disease

idaho forest
A family hikes through an ancient grove of cedar trees in northern Idaho. Trees like western red cedar and western white pine are better poised to withstand changing conditions due to climate change. Lewiston Tribune photo
Climate change may set up one of Idaho’s iconic but downtrodden tree species for a comeback, even as others become more susceptible to fire, insects and disease.

January 1, 2016 — Researchers say in general the state’s diversity of tree species, habitat types and climatic zones leaves its forests well-positioned to adapt to changing temperatures and precipitation patterns.

But there will be an uptick in disturbances across the state’s green zones. There will be and already are more fires. They are starting earlier, burning more intensely and lasting longer into the fall. The now well-known epidemic of bark beetle infestations that has plagued the West in recent decades is likely to continue and perhaps increase in severity.

Root rot, which has taken advantage of the increasing dominance of species like grand fir and Douglas fir, is also likely to thrive as the climate warms. Low-elevation ponderosa pine forests could give way to grasslands, and high elevation species like white bark pine will probably continue to struggle.

But one of the so-called winners in the uncertain shifting of species distribution brought on by the changing climate could well be the long-suffering state tree — the towering western white pine.

U.S. Forest Service researchers Russ Graham and Terrie Jain at the agency’s Rocky Mountain Research Station lab in Moscow said gooseberry, a key plant in the cycle of the fungus that causes white pine blister rust, could wilt under longer and hotter summers. Its leaves will be more likely to dry out in August and September and be less able to transfer blister rust fungus spores to white pine trees. The disease, introduced to North American in the early 20th century, devastated the massive stands of northern Idaho’s white pine forests.

Jain and Graham say the tree already appears to be responding to blister rust, some 100 years after it began killing millions of trees, by turning on long dormant genes that help it resist the malady. Combined with human efforts to raise blister rust-resistant trees and conditions that will make Idaho less hospitable to gooseberry should set the tree up to take advantage of its natural inclination to prosper over a wide variety of elevations and aspects.

White pine and western red cedar, another native species, are deemed generalists and more resistant to fire and insects. Both could gain ground under a changing climate.

“When we look at climate change adaptation, two of the species that are probably going to be very adaptive, no matter what happens, is western white pine and western red cedar,” Graham said.

Idaho’s remarkable diversity in habitat types, tree species and climate patterns, will give its forests the ability to adapt to the changing conditions, according to Graham and Jain.

As Graham explains it, the climate of Idaho is largely influenced by air masses that descend from Canada, flow up from the Great Basin and blow in off the coast of Washington and Oregon. All those systems collide in Idaho’s diverse geography that includes high-elevation mountains such as the Sawtooths, moist mid-elevation forests in the Clearwater and Panhandle regions and dry sage brush-dominated deserts of the Snake River plain.

The increasing presence of fire on the landscape, however, could cause changes in forest type or even a transition from forests to grasslands. Jain said repeated fires in the same locations can damage soil and reduce seed sources. On top of that, reduced moisture in the spring can make it more difficult for remaining seeds to germinate.

“We are seeing that happen in the wilderness areas. Where we’ve had double burns or triple burns, we have large landscapes of just grass,” she said.

Trees stressed by changing precipitation patterns and increasing heat are likely to be more susceptible to bark beetles that can quickly change lodgepole pine forests from a sea of green to one with large pockets of red and then gray as needles die and drop.

As with all climate change predictions, Graham said there is a great deal of uncertainty not only for how much change is in store but how nature will respond to the change. With that in mind, he said the best way for forest managers to prepare for climate change is to do their best to protect and bolster the health and diversity of forests.

For Jeffrey Hicke, an associate professor in the University of Idaho Department of Geography, just acknowledging the climate is changing and will continue to do so is an important planning tool for managers. Forestry has always required its practitioners to look decades into the future. But now they may have to be more flexible in their planning, he said.

That is the approach David Groeschl, state forester at the Idaho Department of Lands, is taking. The agency that manages its forests for timber harvest has started to plan for a changing climate. That entails things like preparing to alter what sorts of species are planted in different places, taking care to curate seed sources from a variety of habitat types, planning for quicker growth brought on by warmer temperatures and more carbon dioxide in the atmosphere, and continuing to manage forests to make them resilient to fire, insects and disease.

He said it’s common for foresters to plan for “future desired conditions.” That has usually meant looking to the past to determine ideal conditions. But foresters more than ever have to look forward.

“We want to have desired future conditions of the forest based on what we think the conditions will be like in the future rather than always looking back and saying we have to mimic the historic conditions that were here,” Groeschl said.


by Eric Barker | Idaho Statesman