Let’s begin with a couple of riddles: What’s bigger than a whale yet hides out of sight?
What could fill 250 semi trucks yet spreads itself thin?
The answer lies in the Blue Mountains of eastern Oregon and it tries to kill whatever it touches. But to see it, you have to know what to look for.
It’s a fungus.
"People don’t think of mushrooms killing trees,” says Greg Filip, a pathologist with the U.S. Forest Service. Trees often benefit from mushrooms at their roots.
Honey mushrooms, however, suck the life out of a number of types of trees. The trees fight back, shoving out the invading fungus, pitch oozing out of holes in the bark. But in many cases it's a lost cause.
“It’s girdled by the fungus,” Filip says. “The fungus will grow all the way around the base of the tree and then kills all the tissues.” Filip stands in the Malheur National Forest surrounded by trees dying in slow motion.
“It could be 20, 30, 50 years maybe before it finally dies,” he says. If you’re thinking of a classic mushroom with a cap and gills and spores, the honey mushroom fits that bill for only a few weeks each autumn.
Most of the year it’s just a thin, white layer that packs a lethal punch. Filip chops with a hand axe at the base of a tree. Higher and higher he removes bark. Even two feet above the roots, he finds a layer of the white fungus. His fingers peel back a layer “like latex paint.” That white fungus spreads up under the tree’s bark and rots its roots.
"Then there’s no movement of water or nutrients up and down the tree when that happens,” Filip says. Back in 1988, Greg Whipple was the first Forest Service employee to realize they had “something different” on their hands. Back then it seemed to cover 400 acres.
Today, its footprint covers more than 3 square miles. “We haven’t seen anything else in the literature that would suggest that anything else in the world is larger in acreage,” Filip says.
They’ve dug out samples far and wide and in every spot they find more fungus. It’s not just the same type of fungus. DNA testing has convinced the scientists this is the largest single living organism in the world.
If you could scoop it all up and pile it together, scientists calculate it could weigh at least 7,500 tons, and maybe up to 35,000 tons. That’s the weight of more than 200 gray whales. This humongous fungus is nothing new.
“When you realize this fungus spreads at 1 to 3 feet a year and you have something that large, you can calculate the age," Filip says. "And we’re looking at something anywhere from 2,000 to 8,000 years old. Its scientific name is Armillaria.
It also has a couple common nicknames, including “honey mushroom” and “shoestring fungus.” Instead of white, rubbery layers, the fungus sends out black fibers underground. The trees’ interconnected roots provide an unwitting pathway for this parasite on the prowl. The honey mushroom exists in other places, like Michigan and Germany.
But Oregon’s is the largest ever measured. Near Glenwood, Washington the fungus has plagued private timber harvesters for decades. In the 1970s, researchers set out to see if they could eliminate the fungus entirely on test plots at a private timber farm.
In some areas, they cut trees and dug out stumps. In others, they went farther and raked out every last fibrous root they could find. This produced the best results with less fungus and more pine trees survived after being planted on this treated ground. The study has continued for more than 40 years.
Dan Omdal, with the Washington Department of Natural Resources, says there’s one significant drawback to the most effective approach. “It’s very expensive and oftentimes prohibitive to do that level of intervention.”
Timber companies can’t afford to dig out every last trace of the fungus. Omdal is trying another approach. Perhaps they can find which kind of trees can best manage to live with the fungus.
On DNR land near Glenwood, they deliberately planted four different kinds of conifers inches from the stump of a tree killed by Armillari. Of the ponderosa pine, Doug fir, western larch and white pine, perhaps one can tolerate the fungus without dying.
“Remember, it’s the baddest fungus on the block,” says Omdal. “We’re looking for a tree that can grow in its presence. It’s foolish to plant the same species where you harvested in areas that are infested by the disease.”
In eastern Oregon, pathologist Filip notes there’s another way to view the humongous fungus: as a helpful invasion. It’s simple nature helping nature. The fungus kills trees, rots them and recycles them back into the soil.
“There’s a wildlife benefit to these trees,” says Filip, “Once they’re dead, they decay, the birds begin to excavate them and use them for cavities." Living on such a scale, under entire forests, scientists say the humongous fungus is not something humans will have much impact on. It’s part of the landscape.