Late in the summer of 2020, as hunting seasons ramped up and the world reeled from the COVID pandemic, a fire ignited in southeast Wyoming’s Snowy Range. 

It sparked to life on Sept. 27 and grew rapidly, fueled by winds that raged to 70 mph. What would ultimately be called the Mullen Fire consumed or damaged dozens of structures over more than 176,000 acres. 

Researchers say the size and intensity resulted from a combination of vast swaths of beetle-killed trees and unusually dry conditions exacerbated by climate change. While fire is natural, and in many ways necessary, biologists and fire managers weren’t sure how a blaze that big would impact the health of the ecosystem. 

Smoke from the Mullen Fire on Sept. 30, 2020. (InciWeb)

A little more than a year later, they have a much clearer picture. In some places, the Mullen Fire burned so hot it sterilized the soil — meaning plant regeneration may take decades. In other places, the threat of invasive plant species looms large, and runoff, erosion and water degradation remain possibilities. But across the bulk of the forest, scientists have found, the fire may well provide long-term benefits to wildlife. It cleared away dead trees that needed to go and ushered in aspens, willows, wildflowers and grasses. 

“Hopefully we have a good snowpack and greater spring rain next year for continued recovery,” said Ryan Amundson, a Wyoming Game and Fish Department terrestrial habitat biologist. 

There’s still much to be learned, but for now, wildlife and land managers are encouraged by what remains from Wyoming’s largest wildfire in recent history. 

Wildlife habitat

Amundson was nervous when he first ventured into the burn area after snow melted and summer began, he said. 

Little moisture fell on the area in April, May and June. Snowpack had been low. Spring regeneration — the plants that usually sprout as soon as the snow melts — was almost nonexistent. Then record high heat in June, cut the growing season short. He wondered if any plants would have a chance to grow back. 

But summer rains arrived. By late September, some aspens in the burn area measured three feet tall. Willows and wildflowers flourished. 

A yellow heart leaf arnica grows in the Mullen Fire burn zone. (Christine Peterson)

“In areas we were assessing in early spring, I thought I was going to see very high shrub mortality, but we just needed to be patient and let Mother Nature do her thing,” he said. 

Not only did species like elk, deer and bighorn sheep survive into this year, they are thriving, said Lee Knox, Wyoming Game and Fish wildlife biologist in the Laramie region. 

Deer killed during this year’s hunting season are fat, nourished by the new growth that sprouted in areas now cleared of stands of dead trees. 

Bighorn sheep will particularly benefit from open areas created by the fire. Sheep need to be able to see long distances, and tree encroachment shrinks their available habitat. Wildlife officials are conducting a study with collared sheep to track their movements and progress in the newly cleared areas. 

The post-burn forage in some places may be so good that Knox is concerned about elk and deer overgrazing the new aspen and willow growth, he said. He and other wildlife biologists will continue to encourage hunters to focus on herds in and around the burn area to be sure the new shrubs have a chance to grow. 

“Deer and elk thrive in successional change,” Knox said. “There’s not a lot for them in old growth forests. They need forbs and grasses and aspen communities to allow them to be fatter and have healthier babies and expand.”

The lack of spring moisture and low snowpack also resulted in minimal runoff and erosion, according to a recent study completed by Game and Fish. 

We won’t try and stop every fire through vegetation management, nor should we try, and we won’t avoid large fires altogether.

Jason Armbruster, Medicine Bow National Forest Brush Creek/Hayden District Ranger

Biologists surveyed multiple places in the North Platte River and several creeks in the area and found some sediment, ash and silt but no population-level impacts on fisheries. 

“We’re not out of the woods yet, but all in all it’s been a good year and we’ve avoided any catastrophic events to our fisheries from the fire thus far,” Game and Fish’s Laramie Regional Fisheries Supervisor Bobby Compton said in a news release.

Invasive species and the future

While many of the fire’s impacts have been a net positive for wildlife, the U.S. Forest Service, Game and Fish and nonprofits are also focusing on invasive species like cheatgrass that tend to flourish after wildfires. 

The Forest Service sprayed herbicides over more than 10,000 acres of forest and wilderness area to try and kill or prevent cheatgrass, said Jason Armbruster, the Medicine Bow National Forest’s Brush Creek/Hayden District Ranger. Cheatgrass offers little to no nutritional value to wildlife and livestock, and tends to outcompete native plants. It also dries earlier in the year and becomes its own fire starter, fueling bigger and bigger blazes. 

Forest officials plan to spray more acres next year. Cheatgrass won’t be eradicated, Armbruster said, but could be controlled. 

The Mullen Fire burned through this area in the Medicine Bow National Forest in 2020. (Christine Peterson)

Volunteers and forest managers also planted about 5,000 bitterbrush and mountain mahogany shrubs. The shrubs are critical foods for mule deer and other species, but they can take time to regenerate in the wild.

“We collected native seeds in the area and grew the shrubs in a nursery,” Armbruster said. “It gives the shrubs a three-year head start.”

Amundson feels hopeful for the future of the Mullen Fire burn area. The Badger Creek fire, a much smaller blaze that burned more than 20,000 acres in 2018 in the Snowy Range, has regrown healthy habitat for everything from mule deer and elk to birds and small mammals. But, he said, regeneration is time consuming. 

As for the rest of the forest, much of which is still covered in thick stands of old timber and long stretches of dead pine trees, the future is less predictable. Forest officials are working through plans to use prescribed burns, commercial sales and mechanical thinning to try and prevent another fire from running through tens of thousands of acres uninterrupted, Armbruster said. 

“We won’t try and stop every fire through vegetation management, nor should we try, and we won’t avoid large fires altogether,” he said. “But we will have an opportunity to set ourselves, and the forest, up for success.”

Christine Peterson

Christine Peterson has covered science, the environment and outdoor recreation in Wyoming for more than a decade for various publications including the Casper Star-Tribune, National Geographic and Outdoor...

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  1. It was good to read about the optimism of wildlife managers. Forests and their wildlife have been recovering just fine after fires for millennia without our help, so I’m not surprised. But the situation is different now. As noted, there still is much to be learned. One-year-old lodgepole pine seedings were hard for me to find this fall, except in one area near Dry Park, and I’m wondering if they will survive the winter and next summer’s drought if it lasts too long. The fire appears to have been hot enough in some places to kill the seed stored in the pine cones, thus it may take an unusually long time for the next generation of trees to become established. It’s doubtful that the soil was literally “sterilized”, except where it was very shallow and there wasn’t much tree growth anyway, but some understory plants were undoubtedly killed. Usually, the root systems of those plants survive and sprout new stems and leaves. Where I looked, I was impressed by how little of the understory recovered at high elevations. It will be interesting to see what develops. Cheatgrass could become a problem at low elevations, but not over most of the burned area, as implied.

  2. The Forest Service exists to serve timber interests, and for no other reason, no matter how they babble on. At best, foresters are pseudo scientists. Similar for “range managers”, who are in service to livestock farmers. Wildlife and fisheries managers often are most sympathetic to the ag crowd, too.

  3. It’s always good to see a Peterson byline in WyoFile. We’ll expect similar updates regarding other fires in the state.