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Near Fairy Creek in the North Bridger Mountains, large patches of trees have been carved out of the forest and downed conifers shelter aspen from browsing elk, moose and deer.

Johanna Nosal, a silviculturist for the Custer Gallatin National Forest, pointed out spots where Forest Service crews cut down conifers and left them “hinged” over aspen suckers. The technique gives the delicate shoots enough sunlight to grow and keeps animals from nibbling on them too much, she said.

Nearby, large piles of woody debris marked areas where Forest Service crews cut down conifers that were competing with aspen for sunlight and other resources. Those piles will be burned during winter months, according to Nosal.

“Without fire or other types of intervention, these conifer species will grow and outcompete the aspen, and the aspen stand will become unhealthy and die,” Nosal said. “In the absence of fire, there’s nothing to keep out the conifers and keep aspen dominant in the area.”

There is no recorded fire history in the forests around the North Bridgers, and the absence of stand-replacing fires due to fire suppression means large trees have grown to dominate the landscape, according to Nosal.

By opening up the landscape in the North Bridgers, officials hope to help aspen thrive and diversify the age classes, sizes and species of trees in the area, she said. Aspen saplings are an important food source for wildlife, and the trees tend to be more fire-resistant.

The work to rejuvenate aspen is a secondary goal in a broader push by the Forest Service to make forests at the northern end of the Bridger and Bangtail Mountains more resilient to diseases and tree-killing insects like bark beetle and mountain pine beetle.

Crews are thinning the forest and clearing out patches of trees in some areas to reduce the number of large conifers, Nosal said. Later on, workers will come back to those areas and plant new seeds, which officials hope will increase the number of younger trees.

“We don’t have a lot of diversity in this North Bridgers landscape,” Nosal said. “We have a lot of old, mature, larger trees and not a lot of young trees.”

That’s a problem, she said, because scientific literature indicates that having diversity across a landscape makes it more resilient to the impacts of insect outbreaks.

“This project area is at a high risk for Douglas fir bark beetle outbreak because we have a lot of old, mature Douglas fir, which bark beetles like,” Nosal said.

“Our data shows that if we get an outbreak in this area, we could have up to 80% of our trees die in our Douglas fir stands.”

Back in 2017, the Forest Service proposed the North Bridgers Forest Health project under a Farm Bill provision that allows officials to speed up logging in areas that are susceptible to insects and disease.

The approximately 2,300-acre timber project calls for forest thinning, scattered clear cuts and other treatments between the Grassy Mountain area in the Bangtails to the Fairy Creek area in the Bridgers. Sun Mountain Lumber out of Deer Lodge purchased the contract for the project.

Corey Lewellen, Bozeman District Ranger for the Custer Gallatin National Forest, said that while crews can treat a maximum of 2,300 acres, the number of treated acres may decrease as the work gets carried out.

The North Bridgers project was designed primarily to keep stands of trees resilient to outbreaks of insect and disease, but other goals included improving aspen health, reducing fuels around the wildland urban interface and supplying wood products to local mills.

After the timber project was approved in 2018, the work was held up due to litigation.

Alliance for the Wild Rockies and Native Ecosystems Council sued over the project in federal court on grounds that its environmental analysis was insufficient. A federal judge ruled against the groups in the summer of 2020, clearing the way for work to begin.

Now, in the fall of 2021, the project’s mechanical treatments are about halfway complete, Lewellen said.

Temporary roads have already been built, and some have already been decommissioned. That means crews have torn up the soil and scattered large logs and boulders around the roads, blocking off motorized or mechanized travel.

Prescribed “broadcast” burning in portions of the forest’s understory may occur in future spring or fall months, Lewellen said. Pile burning — where workers light up big piles of woody debris — could start this winter.

Once large-scale logging is done, hand crews likely need to do some extra work in the project area through the next three to five years, according to Lewellen.

One of the more controversial components of the project — thinning stands of trees the Forest Service classifies as “old growth” — is also underway in one unit of the forest along South Brackett Creek.

In that area, crews have thinned out towering old growth Douglas fir trees, which offer unique habitat and can take hundreds of years to replace.

Lewellen noted that thinning out such trees isn’t something the Forest Service took lightly, but the agency felt it was necessary to protect the remaining trees against environmental stressors like bark beetle.

Removing some big trees makes the general area less attractive to bark beetle, which usually target dense stands, Nosal explained.

What’s abnormal is not that bark beetle outbreaks occur (the species is native to the region), but that trees in many areas are clumped into dense stands, she said. That legacy comes from decades of fire suppression, which is often necessary for protecting private property and other values at risk.

“If we have a fire tomorrow, in some of these stands that we’ve treated — they’ll be more resilient to stressors,” Lewellen said. “As time goes on, I think those trees will continue to respond well.”

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Helena Dore can be reached at hdore@dailychronicle.com or at 582-2628.

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