Question: What does the world's largest living organism do all day? Answer: Pretty much whatever it wants. But very slowly.
The U.S. Forest Service has adopted an informal live-and-let-live policy for the enormous tree killer it calls the "humongous fungus."
The huge root-rot infestation underlies 2,200 acres east of Prairie City in a remote corner of eastern Oregon's Blue Mountains at an elevation of about 6,500 feet near the Strawberry Mountain and Monument Rock wilderness areas.
The Forest Service plans to publish a brochure about the gigantic fungus, Armillaria ostoyae, this summer. "There is no way to eliminate it," said Malheur National Forest ecologist and tree expert Mike Tatum of John Day.
Most people walking by would never know the fungus lurks just below the ground's surface, occupying its time in the quiet business of sending out shoestring-like tentacles called rhizomorphs and wrapping them around tree roots.
Its sheer mass -- it's roughly the size of 1,600 football fields -- makes Herman Melville's fictional white whale Moby Dick seem like a tadpole. And it could get bigger.
In terms of age, Armillaria is a fungiform Methuselah. Researchers say it may have been 100 years old when Alexander the Great conquered the known world in 330 B.C. And some estimates suggest it could be 8,000 years old, said Forest Service researcher Catherine Parks, who has spent 10 years studying it.
Parks, a research ecologist with the Pacific Northwest Research Station in La Grande, led the studies in cooperation with Oregon State University. She said age estimates are based on measurements of its rate of growth, but vary significantly because of the likelihood of weather and climate shifts over the millennia.
Through DNA fingerprinting and a process called vegetative pairing, Parks' research team determined that Armillaria is a single organism and therefore the biggest living thing on Earth. Another Armillaria fungus in a 1,500-acre tract of Ponderosa pine near Mount Adams in Washington state previously had been thought to hold the unofficial title.
Researchers took samples from different sites and grew them together on petri dishes. Instead of forming barrier lines, samples grew together, establishing that they were of the same organism, Parks said.
When word got around, a pesticide applicator in Georgia telephoned Parks. "He said, 'I read about your problem, and I can kill it,' " she recalls. Parks politely declined. Armillaria is just too big, and virtually all of it is underground, she said.
The fungus can be found worldwide, but prefers dense, closed-canopy forests -- the kind that allow hikers to see little of the sky as they tramp along, Tatum said. The only obvious signs of its presence are the gaps created when it kills trees.
Such openings aren't necessarily bad because they allow fungus-resistant tree species and undergrowth to get a foothold, Parks said. And when a tree dies, it recycles its nutrients into the soil for trees that come after it, she said.
Douglas fir and white fir are particularly vulnerable to the fungus here in the Northwest, while Western larch and Ponderosa pine tend to be more resistant, she said.
Armillaria spreads by extending its rhizomorphs through the upper soil and among tree roots, Tatum said. The rhizomorphs can reach out 10 feet and penetrate roots by a combination of enzyme action and physical pressure.
Infected trees can be identified by cutting into the bark above the root. White filaments called mycelia that sap water and carbohydrates from the tree to feed the fungus are always present in infected trees.
"It looks like latex paint," Parks said of the telltale mycelia. "You can peel it off in a layer."
From an aircraft, biologists see "little rings of dead trees" when Armillaria is present in a forest, Parks said. The fungus never kills all the trees, but the rings sometimes coalesce into larger patterns of mortality, she said.
Whether that's good or bad depends on your point of view, but the fungus is part of the ecosystem, Parks said. "If your land management objective is to grow trees, it is definitely counter to that," she noted.
Tatum says a big, hot wildfire might someday cut the humongous fungus down to size. A 5,000-acre conflagration sideswiped it about four years ago, and the flames killed host trees and energized soil organisms hostile to the fungus, he said.
On the other hand, it might get a lot bigger if nature fires no more broadsides its way, he said. "It will always be out there," Tatum said.The Oregonian
