In Fishlake National Forest in central Utah, there is a stand of quaking aspen — Populus tremuloides — that covers about 43 hectares (106 acres) of mountainside. From above, it looks like an ordinary aspen forest. About 47,000 trunks rise from the ground, each one between 80 and 130 years old, each producing the white bark and shimmering leaves the species is known for.

Genetic testing has revealed they are not separate trees. They are 47,000 trunks of a single organism, all sharing one massive interconnected root system underground. The colony is named Pando — Latin for 'I spread.' It is functionally one tree.

Pando reproduces clonally. New trunks sprout from the root system, mature, eventually die — but the root continues, sending up new shoots indefinitely. The above-ground trunks have the lifespan of a tree. The underground organism has, by various estimates, been alive for between 14,000 and 80,000 years. Some studies, weighing climate constraints and growth rates, place the age closer to 16,000 years. Others suggest much older.

Pando weighs an estimated 6,000 metric tons. It is one of the heaviest known living organisms on the planet — and possibly the oldest individual life form on Earth, depending on how you count.

It is also dying. New shoots aren't reaching maturity. Deer and elk graze the young trunks before they can grow tall, and Pando's natural predators — wolves, bears — were hunted out long ago. Without intervention, the colony will collapse within a century.

A single organism that has survived ice ages and human civilization is being eaten alive by deer.