The biggest living thing on Earth is being nibbled to death. Can it be saved?

Pando, a huge aspen grove in Utah, is a single organism that’s lived for millennia. Unchecked grazing is destroying it.

By Craig Welch
Published 11 May 2022, 11:36 BST
01 pando
These quaking aspen trees, in Fishlake National Forest, Utah, form the biggest single organism on the planet. Grazing deer and cattle that munch on newly sprouted trees are threatening the forest's survival.
Photograph by Diane Cook and Len Jenshel, National Geographic Creative

A tree is sometimes more than just a tree. Quaking aspens, North America’s most widely distributed tree, often reproduce through cloning. What appear as individual trees are instead collections of genetically identical stems. White trunks with shimmering leaves—green in spring; yellow, orange, pink, or red in fall—shoot up as suckers from a single massive root system. Each clonal aspen stand is a single being.

A single aspen clone often covers less than an acre, but sometimes more—even much more. Sometimes a tree is its own forest.

In south-central Utah, up near 9,000 feet on the Colorado Plateau, in a stretch of national forest dotted with juniper and sagebrush, there stands a peculiar aspen grove. Instead of dozens or even hundreds of clonal trunks, there are 47,000, all connected to a single root structure. Known as Pando—Latin for “I spread”—this behemoth stretches across 106 acres, an area twice the size of New York City’s Grand  Central Station.

A quaking aspen tree, Pando aspen, in Fishlake National Forest, Utah. The trees are part of a single organism, called a clonal body.
Photograph by Diane Cook and Len Jenshel, National Geographic Creative

Pando is a celebrity. In 2006 it appeared on a postage stamp. In 2014, Utah adopted quaking aspens as the official state tree.  And yet, through the way the land and animals have been managed around Pando, it’s being destroyed, one clone at a time.

Death by a thousand bites

Pando’s magnificence is in its mass. As far as we know, at least above ground, no single living thing on Earth is heavier. At 5.8 million kilograms, this single being is estimated to weigh three times more than the planet’s biggest individual tree, a giant sequoia in California known as General Sherman. Pando is roughly as heavy as 35 blue whales, 1,000 elephants, or all the people who attended the Super Bowl in 2022.

Each trunk in Pando lives 85 to 130 years, and as each dies, new green shoots arise. But now those shoots are being eaten by grazing mule deer and cattle.

Paul Rogers, an adjunct professor of ecology at Utah State University and director of the Western Aspen Alliance, has studied Pando for years. In 2018, he reviewed 72 years of aerial photos and conducted the first comprehensive analysis of this forest. He found fewer trunks were regenerating than were dying. A new inventory in 2021, not yet peer reviewed, shows a still greater excess of deaths.

Precisely how long Pando has lived is not clear; some have claimed it is 80,000 or even a million years old, but both are incredibly unlikely, Rogers says. It’s probably just a few thousand years old—younger, certainly, than the last ice age, which ended about 12,000 years ago.

But humans have subtly altered this ecosystem, by eliminating predators like wolves, bears, and cougars, and by grazing cattle on forest lands. If we don’t find better ways in coming decades to protect Pando from livestock and wildlife, Rogers says, this unusual forest specimen may simply cease to exist.

Aspens will put up new shoots in response to stress, but if those shoots are eaten by grazers like deer or cattle, the young trees don't have a chance to mature.
Photograph by Diane Cook and Len Jenshel, National Geographic Creative

“Imagine walking into a town of 50,000 people where everybody in town was 85 years old,” he says. “That’s sort of the issue with Pando.”

The forest is growing older. But the next generation isn’t surviving. “And it’s happening on our watch,” Rogers says.

The problem with Pando

Pando is a thing of mystery. Beginning a mile east of Mallard Bay, on Fish Lake in Utah’s Fishlake National Forest, its 440 stems per acre—about one every 10 feet on average—spread over tens of thousands of yards of volcanic rock, interspersed with boulders, some as big as cars. How did this beast get so big? Nobody really knows. But the fact that it did, and that aspens are so common in the Northern Hemisphere, suggests there may be even bigger single-clone groves waiting to be discovered.

Rogers has spent endless hours in the sway of Pando. He’s written poetry about it, felt his smallness beneath its bigness. Its peacefulness moves him in ways he’s not quite able to articulate.

The stand was brought to the world’s attention by a University of Michigan scientist named Burton Barnes. In the mid-1970s he walked through it and compared leaves on neighbouring trees, using them to distinguish between stems originating from a single root system and unrelated trees nearby. Decades later, other scientists sampled DNA from 209 stems across Pando. They showed Barnes had been right. This enormous stand of aspens was all one plant.

It has been known for quite some time that Pando has a few health problems. In the late 1980s, as part of an experiment, the U.S. Forest Service clear-cut two small patches. Nothing grew back. In 1992, they cut another area and fenced it off. That part of Pando is now a very dense stand of about five-inch-diameter trees, all about 35 feet tall.

How could that be? If you cut or kill or burn or scar aspen, its response is to make new babies. Stanley Kitchen, an emeritus research scientist with the Forest Service, has seen aspen groves resprouting with 3,500 shoots per acre—“so many that it’s like walking through a corn field.” Fertility isn’t the problem.

In 2018, researchers finally diagnosed Pando’s afflictions with clarity. At 65 monitoring plots, Rogers and a colleague tracked dead and live trees, stem regrowth, shrub cover—and mule deer feces. The strongest indicator of forest health was regeneration, and the presence of deer corresponded with poor regeneration.

From August to October, when flowers and other plants dry out, mule deer graze and browse in Pando, packing on protein for the fall. About that same time, ranchers with permits to graze cows on nearby forest units pass through for about two weeks a year. All those animals converge on Pando’s shoots, mowing them down before they can become trees.

A possible solution

The problem, however, is simpler than its solutions. Deer and elk are managed by the state, which is under pressure to keep populations high for hunting. But hunting isn’t allowed near Pando. It’s a recreation area, popular with tourists. There are even a few cabins. The animals know it’s safe. They’ve learned over decades to gather here.

Rogers has heard all the suggestions: using firecrackers, or shooting at deer with blanks, or chasing them off with all-terrain vehicles. He doesn’t consider those ideas practical. Altering grazing patterns in forests established for “multiple use” isn’t easy either. Some ranchers have run cattle here for generations.

There could be money available to do large-scale fencing from a private donor, but someone would also have to maintain it. And, Rogers asks, do we really want this iconic thing fenced off like in a zoo? “That doesn’t address the root of the problem,” he says.

As it stands, the parts of Pando that aren’t fenced off for research already are developing along a different ecological path, with different understory plants appearing where trees aren’t growing back. Rogers suspects that may be because the lack of adult trees allows in far more light. Dividing Pando into fenced and open areas is “pushing the most uniform forest of its kind we know of in the world in a new direction,” Rogers says.

But in another community on a nearby mountain, Kitchen, at least, sees reason for optimism. There, browsing by elk and cows, along with decades of suppressing wildfires, had allowed fir and spruce to begin taking over aspen stands. Kitchen and others within the Forest Service collaborated with hunters, environmentalists, ranchers, state officials, and landowners. In 2015, a new 10-year plan to save the aspen on that mountain emerged, with support from all quarters. It included more hunting of deer and elk if their feeding on shoots continues to be a problem.

It has not solved all the problems, Kitchen concedes, but it seems to be making a difference. Aspens are resprouting.

Rogers supports attempting such a process at Pando—along with the immediate culling of a handful of deer habituated to the region and some changes to grazing. One way or the other, he says, “we need to stop the bleeding.”


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