A single aspen in Utah spans 106 acres and shares one giant root system

In the mountains of south-central Utah, on the edge of Fish Lake in Sevier County, stands a grove of quaking aspen that looks like an ordinary forest. Tens of thousands of slender white trunks rise from the ground, their leaves flickering in the wind and turning gold in autumn. To a passing visitor it appears to be many thousands of separate trees. It is not. Nearly every trunk in the grove is a stem of one single organism, all connected below ground by a shared root system.

That organism is called Pando, and it spans roughly 106 acres. By the measure of total living mass it is regarded as the heaviest known tree on Earth and one of the largest living things of any kind, a single individual hiding in plain sight as a whole forest.

One organism, tens of thousands of stems

Aspen reproduce not only by seed but by cloning, sending up new shoots from a spreading underground root network in a process called suckering. Each new trunk is genetically identical to the last, so what looks like a stand of individual trees can in fact be a single organism repeating itself across the landscape. Pando is the extreme case: its stems die off one at a time and are continually replaced by new, genetically identical trunks sent up from the same roots.

The numbers are striking. According to measurements of the grove, Pando covers about 106 acres, is estimated to weigh roughly 13.2 million pounds, and features on the order of 47,000 stems. Because every one of those stems shares a single root system and a single genome, the entire grove counts as one continuous living thing, of the species Populus tremuloides, the quaking aspen.

What “largest” actually means

Pando’s fame comes with a common source of confusion, because “largest tree” can be measured in several ways. In forestry, the biggest trees are ranked by the volume of a single stem, and by that standard the giant sequoia known as the General Sherman is the largest single-stem tree. The United States register of champion trees, by contrast, measures the biggest specimen within each species, and Pando holds that title as the largest aspen. When size is defined by total mass and land area occupied by one organism, Pando stands essentially alone. Being at once the heaviest tree, the largest by land area and the largest aspen clone, it occupies a category of its own.

A discovery decades in the making

Pando was not recognized overnight. It was identified in 1976 by the researchers Jerry Kemperman and Burton V. Barnes, the latter of whom had begun examining an unusually large aspen clone southwest of Fish Lake in the late 1960s and early 1970s. Using aerial photography and techniques he had developed for distinguishing aspen clones by their physical differences, Barnes concluded that a stretch of aspen forest covering about 106 acres was in fact a single clone, and he raised the possibility that it might be the world’s largest organism.

For years the finding remained relatively obscure, but later genetic study confirmed the earlier analysis, verifying that the grove was indeed one connected individual. Formal efforts to understand and protect it began through the Fishlake National Forest, the federal land stewards responsible for the site.

How old is it?

Because aspen clones continually replace their stems and roots, Pando’s age cannot be read from tree rings the way a single trunk’s can, and estimates have varied enormously. Speculative figures have ranged as high as a million years. More grounded work has narrowed the picture: charcoal studies published in 2022 place the lower end of Pando’s potential age at around 9,000 years, while a 2024 analysis based on the tree’s pattern of accumulated genetic mutations suggests an age somewhere between 16,000 and 80,000 years, though that research awaits further replication. Even the most conservative of these estimates makes Pando a survivor of the retreat of the last Ice Age, quietly cloning itself since long before recorded history.

An aging giant that needs help

Longevity has not made Pando invulnerable. Beginning in the late 1980s, the Fishlake National Forest started work to remove diseased trees and encourage new growth, including coppicing to stimulate fresh sprouting. The core concern is regeneration: in parts of the grove, too few new stems are surviving to replace the old ones as they die, in large part because browsing animals eat the young shoots before they can mature. Fences have been erected to protect sections of the tree, and a formal protection plan developed between 2015 and 2022 and adopted in 2024 aims to expand wildlife controls and safeguard the organism for the long term. For a single living thing that has endured for millennia by constantly renewing itself, the challenge now is ensuring that renewal continues.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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