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Zach Hedstrom, founder of Boulder Mushroom, holds a mass of wood chips Friday, Oct. 13, 2023, in northwest Boulder. The mass shows mycelial cohesion and matting, a stage at which the chips are unified with higher moisture retention, before the layer’s formation and transformation into topsoil. Wood rotting fungi and other mycelium can have strong enzymatic capacities that easily break down biomass from Colorado’s forests and burn sites. (Olivia Sun, The Colorado Sun via Report for America)

GOLD HILL — Zach Hedstrom kneels on the forest floor, scraping at the 2-inch-deep duff of lodgepole pine needles and pine cones disassembled by squirrels, looking to see whether ghostly fibers of mycelium are quietly consuming the hillside. 

This would be a good thing.

A mushroom-based takeover of a sunny plot previously thinned for wildfire mitigation is actually the goal, not a horror movie nightmare. The fingers of mycelium can claw their way through wood chips, sawdust and broken branches, and quickly break down wood into a damp, fecund strata that promotes plant regeneration at the same time it blocks wildfire. 

What Hedstrom uncovers for an assembly of two dozen Boulder County forestry experts is an inspiring layer of devil’s food cake crumbs shot through with white mycelium strands. Compared to a dusty gray, hard-packed sheet of sand a few feet away that was never treated with fungus, the dark soil is a veritable rainforest. 

“You can feel this and it’s actually spongy to the touch,” Hedstrom says, as the murmuring crowd nods and reaches reverently for soil that is apparently on a miraculous journey back to health. 

Soil from a mycelium treatment area, right, is compared to that of typical soil near Gold Hill. (Olivia Sun, The Colorado Sun via Report for America)

Now the fungi proving grounds need to get much bigger. Hedstrom’s Boulder Mushroom, a host of Boulder County agencies and nonprofits, and foresters in other major Colorado watersheds have science-backed theories that enriching depleted forest soils with fungus can improve public lands throughout the West. The federal government wants to thin trees and reduce fire danger on 50 million acres in the next 10 years, leaving behind overwhelming piles of tree limbs and wood chips that can last decades in arid climates. 

The people of the mushroom want to hand nature back some of its teeth, by broadcasting a carefully selected mix of mycelium across forest floors and open spaces in pursuit of a healthier ecosystem. 

“We are looking for other tools in our toolbox,” Hedstrom said. His metaphor is echoed precisely in the course of a sunny afternoon in the hills above Boulder, by agencies that are partnering with him to pursue fungi dreams. 

“It’s amazing to see the momentum,” said Maya MacHamer, co-founder and director of the nonprofit Boulder Watershed Collective, which promotes forest and wildlife health in the Boulder Creek drainage. MacHamer encouraged the group assembled in the parking lot of Sacred Mountain Ashram to walk with Hedstrom into the surrounding forest and “witness something that’s growing bigger and bigger. And the innovation that the community is welcoming in on many different levels, that is really what’s catalyzing a lot of this work to move forward more rapidly.”

Maya MacHamer of Boulder Watershed Collective speaks to participants in a tour of a wildfire mitigation project in Boulder County. (Olivia Sun, The Colorado Sun via Report for America)

But is the coalition doing it right?

Boulder County’s taxpayer-funded climate innovation fund has staked Boulder Mushroom, the watershed collective, and Grama Grass & Livestock with a $100,000 grant to expand research on mushroom treatment of forest floors. Hedstrom doesn’t claim he can do it alone, but some forestry experts believe the dream of mushrooms chewing up and neutralizing mountains of fire fuel is worth seeding similar startups with public grants. 

Hedstrom’s Boulder Mushroom — “Colorado’s premium center for fungi”! — infuses wood chips with enzymes from mycelium, the root-like threads spreading underground from the classic mushroom cap. While untreated chipped wood can take years to break down under dry Western skies, chips mixed up with fungi break down into productive soil relatively quickly. At the Gold Hill demonstration, Hedstrom showed piles of decaying wood and budding soil that had a good start 16 to 20 months after treatment. 

The process comes with bonus results, like sequestering carbon as vegetation springs up from the spongy mix. 

There’s plenty of territory for Hedstrom’s dream to take root. The U.S. Forest Service is deep into a nearly $5 billion, 10-year program to reduce wildfire danger and improve habitat health on 50 million acres of vulnerable federal and local lands. Colorado’s Front Range is home to dozens of square miles of the thinning plan, which is leaving behind seemingly endless piles of shorn trunks and branches. 

Burning the slash piles is only safe in calm weather, preferably when new-fallen snow dampens the surrounding brush. Local partners like Jefferson County have tried chipping all the trunks and branches and spreading the sawdust on site. But as anyone knows who has a Colorado garden spread with mulch, the chips blithely endure. 

Mushroom-aided breakdown works, as Hedstrom and other researchers, like the Coalition for the Upper South Platte, have demonstrated in artificial windrows of piled up wood chips and on test plots in thinned forests. The problem now is to get the idea to, well, mushroom, to a scale that could have regional impact. 

Once Hedstrom’s crews have grown enough mycelium for a broad treatment, they scatter the spores in clumps of decaying wood and soil by hand. Hedstrom’s more recent addition has been to mix mycelium with water, and spray a decay-inducing liquid out over the same area. The dual treatments should accelerate decay rates, he said. 

This is where the goodwill among wildfire-fighting mushroom advocates begins to take on a danker musk. 

The Coalition for the Upper South Platte has high hopes for mushrooms, but one of its leaders says the Boulder Mushroom faction is overselling its results, using dubious methods through the water-casting of mycelium and threatening everyone’s funding with unserious science. 

“They don’t train their mushrooms,” said Jeff Ravage, a forester and mycologist — fungi expert — with the coalition. The South Platte region has plenty of past and future fire problems of its own, from a heating climate that has stunted some forest regeneration to seemingly endless debris from mitigation thinning and disasters like the 2002 Hayman fire. 

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A truly scientific mycology approach “trains” mycelium starting in petri dishes, Ravage said, refining strains by feeding them what is in effect “90% candy bar and 10% wood chips.” The portion of wood chips from the target debris is gradually increased until the fungi strains are a lean, mean rot-ready machine. Cue “Rocky” and the “Gonna Fly Now” montage. 

Without that kind of scientific rigor, Ravage said, there’s no way to tell if Boulder Mushroom is doing more than the “placebo effect” you would get from spraying water on a forest floor and watching normally paced wood degradation happen on its own. 

Boulder Mushroom says it does train the fungi it uses before they are sent into the wild. “All of our fungal inoculants are grown out on petri dishes in our laboratory first to assess their vigor and train them before use. We get every strain started in this manner prior to application in the field,” Hedstrom said.

Ravage said he hates to criticize those like Hedstrom who want the best for Colorado watersheds. “I’d like to see it work,” he said, “but we keep reaching out to him and he keeps not reaching back. You know?”

“What we’re trying to do is guarantee success by being rigorous about it,” he said. To Ravage, it’s not at all clear yet that mushroom-enhanced decay can jump easily from the windrows the South Platte advocates and Pike National Forest create, with sawdust 4- or 5-feet deep, to a thin layer exposed to air on a broad forest floor or open meadow. 

Hedstrom knows Ravage is a vocal critic, and Hedstrom does not appear to be ruminating while he is germinating. Hedstrom said Ravage has never contacted him.

“We’ve also conducted our own studies using our own methods, and a lot of them are, in fact, quite similar” to the South Platte group’s, with similar results, Hedstrom said. “From what I can interpret here, we’re really trying to address the scalability aspect of this work.” 

Ravage’s team has done pilot work on smaller plots, a few square meters at a time, Hedstrom said, where “we want to be able to bring this into an operational capacity, which is why we’re looking at solutions to be able to treat multiple acres.”

For Hedstrom, the promise of the premise is always right there, in the lacy white fibers of feeding mycelium tangled up in decaying soil. 

“At Gold Hill,” Hedstrom said, “we dug down into those chips. And you could visibly see them.” 

Update: This story was updated on Oct. 26, 2023, with more comments from Boulder Mushroom about how it trains fungi.

Michael Booth is The Sun’s environment writer, and co-author of The Sun’s weekly climate and health newsletter The Temperature. He and John Ingold host the weekly Sun-Up podcast on The Temperature topics every Thursday. He is co-author with...