Scientists say key to burned tree re-growth in Sonoma County is: fungus

In the heart of fire-swept Trione-Annadel State Park, blackened columns of Douglas Fir, bare exposed earth, and the ghostly gray limbs of oak, madrone and bay still stand on the steep ridges and rolling hillsides between Oakmont and Bennett Valley.

Amid the devastation, meadows have sprouted with new green grass, and patches of tiny, orange, cup-like Anthrocobia - mushrooms that appear only after fire - have emerged among the white ashes, a strange splash of color amid the black and white landscape.

But the regeneration of the forest itself hangs, literally, by a delicate thread.

Down in the smoke-scented soil, beneath the dark char and white ash, tiny tendrils known as mycelia, thin as spider silk, are spreading. And their survival is key to the restoration of the woodland giants towering overhead.

In winter, when the rains come to California, some of these important forest dwellers betray their presence, sending up the mysteriously shaped and colored fruiting bodies we know as mushrooms.

But the fungus below them, the invisible living organisms that bear the mushrooms, are busy all year.

If we could see them, they'd be everywhere, an interwoven network of microscopic filaments, running through the layers of soil, within the leaf litter, beneath bark and in the living wood, and in everything that's decaying.

At UC Berkeley, Tom Bruns, a researcher and fungus expert, or mycologist, has spent decades studying the hidden world of fungi in the wild, and their relationships with living plants.

“There's a lot we don't know,” he said, “but we now estimate 90 percent of all plant species live in association with fungal partners. They're absolutely everywhere.”

And, without their fungal partners, it's now known, many seedlings and trees will simply not survive.

The mycorrhiza fungi send their filaments out into the surrounding soil, gathering water and essential nutrients like nitrogen and phosphorus, which they transport back to the tree. Their branching mycelia are so incredibly fine that a cubic inch of soil can contain a mile or more of them. As a result, they extend the tree's reach to critical food and water by ten to 1,000 times.

In exchange, Bruns explained, the tree provides them with sugars and carbon, which the growing fungus can't produce themselves.

“Up to 20 percent of the sugar energy and fixed carbon produced by tree leaves using sunlight, is transported to the fungal mycorrhiza,” Bruns said, adding that individual types of trees and plants can each have their own particular fungal partners.

Fungus pipelines

And what's more, this so-called “wood-wide web” has recently been found to connect trees and stands of forest together. In 2016, researchers in Switzerland tracked the movement of tracers, and discovered that carbon absorbed by the leaves of one tree appeared in the tissues of separated neighboring trees, transported there by fungus pipelines.

So, what happens to this essential, delicate fungal network when the forest catches fire?

Most of them are destroyed and disappear, Bruns said, depending on how hot the fire burns, and for how long. But, he noted, many species found here have adapted to the California ecology, which is prone to regular fires.

Here, burning is a natural part of the life cycle of forests and plants. And the fungi have a few survival tricks up their sleeve.

Adaptation strategies

One of Bruns' former student researchers, Sydney Glassman, has studied the effect of fire on the mycorrhizal fungi in Sierra Nevada forests.

Now an Assistant Professor at UC Riverside, Glassman found that while fires do wipe out vast amounts of the fungal networks, and it can take a very long time for all of the species to recover, some survive by storing banks of spores deep in the soil.

Soil is a fairly good insulator against heat.

And one type of fungus, Glassman explained, of the genus Pyronema, from the Greek word pyro, meaning fire, is so specially adapted that it only emerges in abundance following the passage of flames.

Indeed, in Trione-Annadel today, the Anthrocobia have already erupted.

Fires' aftermath

Another way the fungi survive, Glassman said, has to do with the nature of wildfire itself. Up in the forests of Trione-Annadel, the fire did not cut a uniform swath of destruction. In places, one can hike for minutes at a time through landscapes marked by extreme heat and flame, with blackened bark and leafless limbs a hundred feet above bare ground.

But just around a corner, it's clear the fire passed through more quickly.

Singed patches of moss and ferns, still green, sit like toupees on top of burned boulders, and twenty feet off the ground, above a strata of dead brown, green leaves still grow.

This patchwork pattern of fire damage is normal, and important, according to Cyndy Shafer, the Natural Resource Program Manager for California State Parks Bay Area district.

“It leaves small reservoirs of plants and seeds needed for regeneration,” she explained.

In Trione-Annadel, she said, this mosaic is clear in maps produced after the fires that show how uneven the burn was in different areas. In many spots, the fire damage was low to moderate severity.

But the delicate and slow process of recovery, Shafer explained, is why the burned section of the park is still strictly off limits to the public (special access was granted for this article).

Shafer acknowledged the concern and curiosity many have for one of the region's beloved parks and made a plea for the public to understand: “Not being able to get in for a time is sacrificing in the short term, for the long-term health of the park,” she said.

So will the mycorrhizal fungus of the native oaks and woodlands revive and rebuild the forest?

That's a question Gabriel Reuben Smith, a Stanford Ph.D. student, will be studying this winter in the unique fire-scorched laboratory of Trione-Annadel and Hood Mountain parks. Smith works in the lab of mycologist Kabir Peay, another of Tom Bruns' former researchers.

Coping with fires

To get through a burn, Smith explained, one of the main adaptations of mycorrhizal fungi is to leave a spore bank, in resistant, bud-like structures down in the soil. Some species produce huge amounts of spores that are quite long-lived, and resistant to heat.

“These spores can remain dormant in soil for many, many years,” Smith said.

“Even if everything else gets killed by a wildfire, those spores will be there for the first tree seedlings that begin to take root in the aftermath, and they will come to life when they sense a seedling nearby.”

However, Smith noted, while oaks and other Sonoma hardwoods have mycorrhizal partners, it's not clear if, or how, their recovery will play out in local woodlands.

No one has ever studied the mycorrhizal fungi network in the oak forests of California after a fire - his study will be the first.

In nature, many of the essential links that support life lie hidden, until disaster strikes.

Then, as in human communities, the recovery of the whole depends on the efforts of a few resilient networks, coming together, working behind the scenes.

Stephen Nett is a Bodega Bay-based Certified California Naturalist, writer and speaker. Contact him at snett@californiasparks.com.