Pando

Pando, in Utah, is a single aspen clone made of about 47,000 stems joined by one root system. It covers 43 hectares and weighs about 6,000 tonnes.

Some fungal colonies cover more area but weigh less.

Context

Pando, whose name is Latin for 'I spread', grows in Fishlake National Forest in south-central Utah. What looks like a forest is a single genetic individual: every stem is a genetically identical copy, connected below ground by a shared root network. Researchers identified the clone as one organism by comparing the genetic makeup and traits of the stems, such as the timing of leaf change in autumn.

The weight comes from an estimate, not a weighing. Scientists counted stems, measured their sizes, and used formulas to work out the overall mass of roots and trunks. The figure of about 6,000 tonnes is therefore approximate, and the stem count of about 47,000 changes as stems die and new ones sprout.

The clone's age is uncertain. Estimates run from several thousand years up to far higher numbers, but individual stems live only about 100 to 130 years, and the root system is what persists. Because it is hard to date, any figure should be treated with caution.

Pando is not doing well. Grazing by deer and cattle has prevented many young stems from surviving, and managers have used fencing and other measures to help regeneration.