What the World’s Largest Organism Reveals About Fires and Forests

Despite concerns raised by Weaver and others in the field, fire suppression became a cornerstone of forest management. And at first, coinciding with a relatively cool, wet period, it seemed to work. Fires across the American West were limited and generally controllable. For about 50 years, this fire regime was presumed to be normal. The main goal of the forest service during this era was to support the timber industry and, for decades, it thrived in a stable, fire-free environment. Forests were first cleared of old growth, because large trees made more money than small trees. New-growth trees were then seeded on a grid-like pattern, and reliable, fast-growing species, such as fir trees, were preferred.

As a result, there are now more fir trees in western forests than there should be. Douglas firs and grand firs, specifically, are common—and are not adapted to withstand fires. Though these firs are native, they are proliferating in “non-native numbers,” says McWilliams. A 2017 study in the journal Trees, Forests and People found that firs and other species lacking fire adaptations are nine times more common today than in past centuries—in some areas, they comprise more than 90 percent of a forest’s tree mass.

Douglas firs and grand firs have allowed something else to happen. These species are highly susceptible to infections of the fungus A. ostoyae. While the Humongous Fungus predates 20th century forest management through fire suppression by thousands of years, it probably would not have gotten so enormous without it.

The A. ostoyae specimen known as the Humongous Fungus is not alone; in the late 20th century, another outsized Armillaria, this one in Washington State, achieved similar proportions. “I always say that this is the largest documented organism,” McWilliams says. “It’s highly likely that there’s a bigger one out there somewhere.”

Ironically, these giant fungi slowly destroying the forest may also be tools to help it recover from a century of problematic fire management—and to protect it from a changing climate that’s hotter, drier, and at greater risk for catastrophic fires.

While it’s unclear whether a fire burning above it would damage the Humongous Fungus itself, McWilliams notes that in areas of the forest where Armillaria infection is most advanced, trees are spaced further apart and organic material on the ground has been broken down. As the Humongous Fungus and other Armillaria expand at a rate of up to 5 feet per year in all directions, they chomp through the highly susceptible Douglas firs and grand firs—creating space, and filtering nutrients back into the soil, to support the potential growth of species more resistant to fire (and fungus). Eventually, Armillaria could clean out all the overgrowth and natural debris on the forest floor—but not on a timeline that’s acceptable to humans.

Now, more forest management experts are starting to reintroduce fire into the landscape across the American West through small, highly controlled fires known as prescribed burns. Intentionally setting fires can be politically tricky, even in communities where people understand the benefits, but, says McWilliams, “You’re going to have smoke one way or the other. Do you want a little bit of smoke one day or a lot of smoke when you can’t control it?”

He and other forest scientists hope that we can restore our symbiotic relationship with the forest, aiding the cycles of natural fires that benefit many fire-adapted species, and respecting the ecosystem’s natural rhythms.

Meanwhile, the Humongous Fungus of Malheur National Forest will keep growing.