Earth's Oldest Living Organism May Not Be What You Think

What might be the oldest living thing on Earth lives on the side of a highway in Utah, and many people drive right through it without even noticing. It looks like a forest of aspen trees but is actually a single organism, one that originated from a single seed that managed to clone itself tens of thousands of times. The trees all share the same root network, covering 106 acres within Fishlake National Forest. At an estimated weight of 13 million pounds, it is the largest living organism by mass in the world, over 5,000 times heavier than a bison, the biggest land mammal in the United States.

The scientists who discovered this remarkable aspen collective in the 1970s named it Pando, a Latin word meaning "I spread." A scientific study posted on bioRxiv in October 2024 used over 500 DNA samples to gauge Pando's age, landing on an estimate of 34,000 years, with a potential range of between 16,000 and 80,000 years old. While the study is still awaiting peer review, the findings would make Pando both the oldest-known living organism and the largest. It begs the question: how does one little tree grow to become such a dominant and enduring force?

Pando is a quaking aspen (Populus tremuloides), so named because it has flat leaves with long stems that quiver at even the faintest hint of a breeze. The quaking aspen is the most widespread species of tree in North America, partly thanks to the fact that it is an asexually reproducing organism. Although aspens do produce pollen and eggs in their flowers, meaning they are technically capable of sexual reproduction, they tend to favor the simpler approach of cloning themselves.

To do so, the aspen sprouts a new stem from its root system, which bursts through the soil and becomes a trunk from which new branches and leaves grow. From the surface, the stem appears to be an entirely new tree, but there are clues that reveal the true nature of the situation. For example, all of the trees that make up a clonal colony such as Pando grow their flowers and shed their leaves at the same time each year.

The original stem of Pando sprouted during the last ice age, but that stem has long since died. Although aspen clones can live for thousands of years, the individual stems only live about 50-150 years each before dying off and being replaced by new growth. Today, Pando is made up of roughly 47,000 stems (trees), the oldest of which are estimated to be around 130 years of age. Theoretically, Pando could continue to grow indefinitely, but unfortunately, the opposite appears to be happening.

Aerial photographs of Pando taken over the past seven decades show a steady downward trend. Gaps have appeared within the clone, showing stems are dying off without being replaced. The stems that make up Pando at the moment are almost all in the late stages of their life, so it's essentially a population of senior citizens with nearly no young or even middle-aged individuals in line to fill their place. As for why Pando's stems are dying faster than they can reproduce, the main culprit is grazing by animals in the woodland ecosystem.

Mule deer are a particularly problematic species for Pando, eating new sprouts before they can grow into full trees. The deer population has been allowed to grow unchecked since the early 1900s, when hunters took out many of their natural predators, such as wolves and mountain lions. Cattle are another major threat. Some National Parks allow seasonal livestock grazing on their lands, and cattle typically graze in Fishlake National Park for a couple of weeks each year. In this short time, they eat tremendous amounts of undergrowth around Pando.

In response to these threats, the Forest Service built protective fencing around parts of Pando, which have since seen a resurgence. However, as of the writing of this article, only about half of Pando has been fenced off, and the unprotected areas are still struggling. Pando has proven its resilience for tens of thousands of years, so hopefully, it can keep tacking onto its record age.