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Like Fungi in the Bank: Sierra Nevada Forests Invest in Fire-Withstanding Fungi

March 17, 2016
by Chelsea Leu

The Rim Fire, sweeping through the Sierra Nevada in 2013, rendered 257,000 acres of vegetation into ash, razed whole stands of trees, and ranked as the third biggest wildfire in California history. But the conflagration also sparked a discovery, if you happened to be a mycologist running a field experiment in the area. UC Berkeley Ph.D. student Sydney Glassman was simulating the effects of disturbances on fungi in pine forests when she discovered that nature had already done most of the work for her: Of her lab’s 19 test plots nationwide, 2 in the Stanislaus National Forest had been burned. So she gathered new soil samples, planted some seedlings for the fungi to grow on, and waited.

These species were surprisingly resilient to high heat, and in a paper published last October, the scientists dubbed them “fire fungi.”

Part of the reason the Rim Fire caused so much devastation was that the forests weren’t adapted to catastrophic, high-temperature blazes. But after a few months, Glassman’s pine seedlings started to grow. And so did the spores on them—a raft of 30-odd fungal species (including varieties such as Rhizopogon olivaceotinctus and Wilcoxina mikolae) that had withstood the flames and lived for scientists to tell about it. “There were certain fungi that actually increased in frequency and abundance after the fire,” Glassman says. These species were surprisingly resilient to high heat, and in a paper published last October, the scientists dubbed them “fire fungi.”

Because of their unusual hardiness, the fire fungi are crucial to a forest’s regeneration after severe wildfires. As ectomycorrhizal fungi, they have a mutually dependent relationship with the pines. “It’s sort of a chicken-egg scenario—the fungi need the tree, and the tree needs the fungi,” Glassman says. “The trees can’t grow without them.” The bargain goes something like this: The fungi, living at the tree’s roots, enable the trees to slurp up more nutrients and water from the soil, and receive photosynthesized sugars in return.

So the fungi’s spores act sort of like a safety deposit box buried in the ground, a rainy day fund for unprecedentedly large infernos. And after the Rim Fire, the investment paid out: When Glassman returned to her plots two years later, the area was green with shrubs and pine seedlings. If the ecosystem develops normally, new species, including new fungi, will arrive to repopulate the landscape, and the fire fungi will retreat. “When a forest is healthy and active, they’re going to be sitting around as spores, waiting for a disturbance to happen,” Glassman says.

But when disaster strikes again—an increasingly likely occurrence, Glassman points out, as the warmer springs and drier seasons of climate change herald more mega-fires—the spores will be ready.

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