acquired August 11, 2021

Saving a Forest of One



When viewed from hundreds of kilometers above Earth, this patch of aspen foliage in south-central Utah looks somewhat ordinary. But the leaves belong to a colony that is actually quite extraordinary. More than 40,000 genetically identical trees are connected by a common root system, and are part of a single massive organism, a male quaking aspen (Populus tremuloides), that scientists have named Pando, which means “I spread” in Latin.

In this fall image (above-right), acquired with the Operational Land Imager-2 (OLI-2) on Landsat 9, Pando’s yellow leaves are visible for about 200 meters on either side of State Route 25 just west of Fish Lake. The darker green forested areas surrounding it are dominated by evergreen trees, including spruce and fir. Many of the other yellow areas in the image are aspen stands that are not part of Pando.

Pando’s trees and root system span 106 acres (43 hectares) and weigh 13 million pounds. That is roughly the size of 80 American football fields and the weight of 15 jumbo jets, making Pando among the largest and heaviest land organisms on the planet. (Offshore, sea grass and coral reefs also grow to vast sizes, but likely do not carry the immense weight of Pando.)

The precise age of Pando’s root system is difficult to determine. But scientists think the aspen seed that started the plant sprouted several thousand years ago, perhaps even as long as 14,000 years ago as ice retreated from the Fish Lake Valley after the height of the last glacial maximum. Since sprouting, that seed has grown and spread by sending up new shoots every spring from its root system. These shoots—sometimes called suckers or ramets—are recognized as trees as they grow to maturity. They typically persist for about 100 to 150 years before dying back, even as Pando sends up more shoots and lives on.

But Pando has not been well in recent decades. “It’s dying,” said ecologist Paul Rogers, the director of the Western Aspen Alliance at Utah State University. “Mule deer—and to a smaller degree cattle—frequent this area in such numbers that they are grazing on the young shoots and stopping them from getting established. If you think of Pando as a village, it’s a village full of old people with very few children growing up to take their place.”

Rogers and a colleague from Utah State University first reported in 2018 that Pando was in trouble. Field measurements and a series of historical aerial photographs made clear that the forest has thinned considerably since the 1930s. In that study, and in an update published in 2022, Rogers reported that the only parts of Pando that were showing signs of regrowth were the parts that were fenced off from deer and cattle. The photograph below, taken by Rogers, shows more growth of young stems on the inside (left side) of one section of fencing.

acquired September 15, 2018

However, Rogers wonders about how large a role fences should play in trying to save Pando. “Is fencing Pando off like a zoo animal the right solution?” he asked. “We also need to look at things like predation and what can be done to keep deer populations at more sustainable levels to address the problem in a more comprehensive way.”

For Rogers, the challenges and management questions don’t end at Pando’s edges. “Pando, though charismatic and fascinating, is a microcosm for much bigger, more global issues,” he said. “We have to think not just about Pando, but about how we keep aspens—forests more broadly—all over the world healthy and thriving as the climate changes and people put increasing pressure on ecosystems.”

That is going to require a change in perspective that expands far beyond Pando or this one part of Utah, he added. “This Landsat image is a reminder of how small even one of the world’s largest organisms is from a planetary perspective. We’re going to need monitoring and conservation of aspen forests on a global scale.”


NASA Earth Observatory images by Lauren Dauphin, using Landsat data from the U.S. Geological Survey. Photo by Paul C. Rogers (Western Aspen Alliance). Story by Adam Voiland.