Montana mycologist fights fungus with fungus

To save whitebark pines, apply slippery jack.

 

When most Westerners venture into the woods in search of fungus, they’re looking for dinner. When Cathy Cripps goes mushroom hunting, she’s trying to save a tree.

The tree in question is the whitebark pine, an iconic species that’s been devastated throughout the Northern Rockies by mountain pine beetles and a fungal disease called blister rust. We’re accustomed to thinking of fungi as a danger to biodiversity: In addition to pines, witness bats and frogs, imperiled by white-nose syndrome and chytrid, respectively. But Cripps, a mycologist at Montana State University, is captivated by the opposite story — a certain fungus may yet be what whitebark pine needs to survive. 

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Whitebark pines are listed as warranted but precluded from protection under the Endangered Species Act. Photo courtesy of the National Park Service.

That notion emerged from years of fieldwork in whitebark pine forests throughout the Greater Yellowstone Ecosystem. There, Cripps noticed that the soil was rife with a particular fungal species: Suillus sibericus, aka Siberian slippery jack. Suillus sibericus is a mycorrhizal fungus, meaning that it forms close symbiotic relationships with the roots of plants. The fungus draws sugar from roots, and in turn pipes nutrients back to its host tree through an underground network of fine filaments. “Each root tip gets surrounded by the fungus, just like a little sock,” Cripps says.

Cripps wondered if mycorrhizal fungi could change the survival odds for whitebark pine seedlings grown in nurseries and planted for restoration. Cultivating whitebarks is an arduous process — among other complications, the seeds have to be exposed to elaborate temperature cycles in order to germinate — and not always successful. One graduate student who surveyed more than 100,000 whitebark seedlings planted in the region found that just 42 percent lived.

That low success rate is partly due to the fact that whitebark seedlings are often outcompeted by rival trees, like spruce and fir. Slippery jack offered a solution: While many other mycorrhizal fungi are “promiscuous” — they partner with more than one tree species — S. sibericus almost exclusively cohabitates with whitebark and its relatives. “We figured sibericus would give whitebark pine an advantage, without helping the tree species that are competitive with it,” Cripps says.

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Siberian slippery jack, Suillus sibericus, might just be key to whitebark pine's survival. Photo courtesy of Anna Baykalova.

That’s when the hunt began. Cripps and a graduate student named Erin Lonergan foraged for slippery jack’s lemon curd-colored mushrooms in the mountains around Yellowstone and Canada’s Waterton Lakes National Park; back at MSU, they used a coffee grinder to mill the underside of the mushrooms, where spores reside, into a powder. Finally, Cripps diluted the powder with water and employed an inoculation gun — the kind you’d use to vaccinate cattle — to implant her spore concoction into the soil around whitebark seedlings growing in the Glacier National Park nursery.

In September 2010, volunteers planted about a thousand seedlings from the Glacier nursery at test sites across the border in Waterton. This summer, Cripps and Lonergan reported that, after three years, the fungal inoculation had enhanced survival by 11 percent. “Given how difficult it is to grow seedlings, even a small increase in survival is very important,” Cripps says.

Parks Canada agrees with her: They’ll be using slippery jack on future whitebark plantings in Waterton, Banff and Jasper National Parks. (Nurseries in the U.S. haven’t yet committed to the technique, but they’re interested.) Cripps still isn’t positive how slippery jack benefits pines, though she suspects it aids the tree by helping it take up nitrogen. Just as scientists are still coming to understand how certain trees die, they have a ways to go in figuring out why others live.  

But for all the concern about whitebark survival, Cripps is equally worried about the other side of the symbiotic coin. “If you have a whitebark pine ghost forest where all the trees are just skeletons," she wonders, "how long can these specific fungi persist in the soil?”

Ben Goldfarb is a Seattle-based correspondent for High Country News.