Pando: How the World’s Largest Organism Faces an Uncertain Future

High on the Wasatch Mountains in the western United States, above a lake fed by springs, lives one immense organism that sustains an entire ecosystem on which plants and animals have depended for millennia.

In my home state of Utah stands “Pando”, a 106-acre grove of quaking aspen clones.

Though it appears to be a woodland of separate trees, marked by bright white bark and small leaves that tremble in even the lightest wind, Pando – Latin for “I spread” – is in fact made up of 47,000 genetically identical stems growing from one connected root system.

This single genetic organism has a mass of roughly 6,000 metric tonnes. Measured by mass, it is the largest individual organism on Earth.

Aerial outline of Pando, with Fish Lake in the foreground. (Lance Oditt/Friends of Pando)

Aspens form clonal groves in other places too, but Pando is remarkable because of its vast scale. Most clonal aspen groves in North America are considerably smaller; those in the western United States average only 3 acres.

Pando has existed for thousands of years – possibly for as long as 14,000 years – even though individual stems generally survive for only around 130 years. Its age and isolated location have allowed an ecosystem containing 68 plant species and numerous animals to develop and flourish beneath its canopy.

That entire ecosystem depends on the aspens staying healthy and standing. Although the US National Forest Service protects Pando and it is not at risk of being felled, several other threats could cause it to vanish.

Deer are eating the youngest ‘trees’

Excessive browsing by deer and elk is among the most serious concerns. Wolves and cougars once controlled their populations, but the loss of these predators has left much larger herds.

Deer and elk also gather in Pando because the woodland’s protected status means they cannot be hunted there.

Deer eating Pando shoots. (Lance Oditt/Friends of Pando)

When older stems die or topple, sunlight reaches the forest floor and triggers the growth of fresh clonal stems. However, when these animals eat the tops of the emerging stems, the stems die. Consequently, much of Pando has very little new growth.

One area provides an exception. It was fenced off several decades ago while dying trees were removed. By keeping out elk and deer, this enclosure has enabled new clonal stems to regenerate successfully, creating dense growth known as the “bamboo garden”.

Diseases and a changing climate

At least three diseases are also affecting Pando’s older stems: sooty bark canker, leaf spot and conk fungal disease.

Plant diseases have evolved and persisted in aspen groves for thousands of years. Yet, with little regeneration and a growing number of pressures on this clonal giant, the ecosystem’s long-term response remains unknown.

Climate change is the most rapidly intensifying threat. Pando emerged after the end of the last ice age and has since experienced a largely stable climate.

Pando has survived disease, hunting, and colonization. (Lance Oditt/Friends of Pando)

It grows in an alpine landscape surrounded by desert, so warm conditions and drought are not unfamiliar to it. Even so, climate change threatens both the tree’s size and lifespan, along with the entire ecosystem it supports.

No scientific research has examined Pando specifically, but aspen groves have struggled under climate-related pressures. Reduced water availability and warmer weather arriving earlier in the year can make it more difficult for trees to produce new leaves, contributing to declines in coverage.

As competition increases for shrinking water supplies – while nearby Fish Lake remains beyond the reach of Pando’s roots – summer temperatures are forecast to keep reaching record highs, and more severe wildfires are a possibility. Pando will therefore find it difficult to adapt to these rapidly shifting conditions while retaining its present size.

The next 14,000 years for Pando

Nevertheless, Pando is resilient. It has already endured swift environmental change, notably following European settlement of the region in the 19th century and the expansion of recreational activities during the 20th century. It has previously faced disease, wildfire and grazing, and it remains the world’s largest scientifically documented organism.

For all the reasons to be concerned, there is also hope. Scientists are helping to reveal the basis of Pando’s resilience, while conservation organisations and the US Forest Service are working to safeguard the tree and the ecosystem linked to it. The Friends of Pando also seek to make the tree virtually accessible to everyone through 360-degree video recordings.

During one summer visit to my family in Utah, I seized the opportunity to see Pando. Over two remarkable days, I walked beneath tall, mature stems that swayed and “quaked” in a soft breeze, through the dense young growth of the “bamboo garden”, and into delightful meadows that break up parts of the otherwise enclosed centre.

I admired the wildflowers and other plants flourishing in the dappled canopy shade, and enjoyed seeing pollinating insects, birds, foxes, beavers and deer, each using some element of the ecosystem Pando creates.

It is experiences like these that show us there are plants, animals and ecosystems worth safeguarding. At Pando, we have the unusual opportunity to protect all three.

Richard Elton Walton, Postdoctoral Research Associate in Biology, Newcastle University.

This article is republished from The Conversation under a Creative Commons licence. Read the original article.

An earlier version of this article was published in November 2021.