The Pando aspen clone in Utah is thought to be 80,000 years old, but some think it could be ten times older. It’s hard to guess age and long-term research would have had to begin when humans were starting to emigrate out of Africa.
While Pando isn’t technically the oldest individual tree, this clonal colony of Quaking Aspen in Utah is truly ancient, and at 6,615 tons, it is also the heaviest known living organism on earth.. The 105-acre colony is made of genetically identical trees, called stems, connected by a single root system. Pando is located in the Fishlake National Forest, near Fish Lake on the Fish Lake Plateau located at the western edge of the Colorado Plateau in South-central Utah.
The “trembling giant” got its start at least 80,000 years ago, when all of our human ancestors were still exploring the Great Rift Valley. But some estimate the woodland could be as old as 1 million years, which would mean Pando predates the earliest Homo sapiens by 800,000 years.
Some experts speculate that less well-studied Quaking Aspens in Utah may be 80 hectares in extent and one million years old. Some scientists think that portions of Pando's root system may be dead and might have led the plant to split into separate groups and therefore would not be one organism, though the collective groups would remain the same singular, genetic individual.
The Pando's current 80,000 year designation is based the evidence indicating that there are few if any naturally occurring new aspens in most of the western United States since a climate shift took place 10,000 years ago and eliminated favorable soil conditions for seedling. Successful seeding has not occurred in the western United States since the last glaciation, some 10,000 years ago due to the rarity of a favorable suite of conditions in semiarid environments.
Individual trees have a lifespan of about 200 years, but clones — considered as as a single entity — can sprawl for acres, all descended from one original tree, and are able to reproduce indefinitely.
In a recent study, the oldest clone, estimated to be 10,000 years old, produced one-fourth the pollen of younger clones. Extrapolating, it shouldn’t take more than 20,000 years for pollen production to cease altogether when the clone will still be able to copy itself through its roots, but it won’t be able to make seeds and capacity for sexual reproduction will be extinguished. Without seeds, the clone will be immortal but stuck in place, exposed to disease, drought, fire, and climate change.
“There’s a slow and steady loss of fertility with age,” said San Diego State geneticist Dilara Ally in an interview with wired.com. “Because we were able to calculate the rate at which male fertility was lost, we could estimate how long it would take fertility in the oldest clone to dwindle away entirely.”
“You’re at risk of going extinct if you lose your sexual fitness, because you have no other way of dispersing into a different environment,” said Ally. “Once you get to the point of no return, where your sexual function is no longer capable of operating, then how do you persist in a changing environment?”
The seeds of the aspens’ doom lie in their immortality’s mechanism. While traits like root growth or leaf respiration or disease resistance are immediately subject to the pressures of natural selection, sex doesn’t much matter for an individual tree. Even if seeds are defective, root clones suffice for reproduction. Sex-related mutations can freely accumulate — and by the time seeds are needed, it’s too late.
Sexual selection may still take place, only at some evolutionary scale beyond immediate comprehension, where generations are measured in millennia. For now, such speculation is beyond the scientific horizon.
“I never really believed that anything could live forever,” said Ally. “We just didn’t have a way of showing how they aged."Other candidates for oldest or heaviest living organisms include the possibly larger fungal mats in Oregon, the ancient clonal Creosote bushes, and strands of the clonal marine plant Posidonia oceanica in the Mediterranean Sea.