Pando: The silent giant battling for survival against modern threats

In the Wasatch Mountains in the western United States, there is Pando, a 43-hectare quaking aspen grove considered the largest single organism on Earth by mass. Although Pando is legally protected and not directly threatened by humans, there is a risk of its disappearance due to other natural factors.

"Pando" (from Latin "to spread") is located in Utah. At first glance, it looks like a forest made up of individual trees with characteristic white bark and small leaves that move even in the lightest breeze. It's a 43-hectare complex of quaking aspen clones, consisting of 47,000 genetically identical stems growing from a single, interconnected root network.

Most aspen clones in North America are much smaller, with those in the western United States typically covering only about 1 hectare. Pando has existed for thousands of years, with some estimates as high as 14,000 years, even though individual stems live only about 130 years. Its extraordinary longevity and vastness have allowed an entire ecosystem, encompassing 68 plant species and numerous animals, to develop and survive in its shadow.

Scientists have estimated that the organism weighs around 5,443 tonnes, making it the largest single organism on Earth by mass.

The entire ecosystem relies on the health of the Pando complex. Although it is protected by the US National Forest Service and not at risk of logging, its disappearance could be caused by several other factors.

As reported by ScienceAlert, one of the biggest threats to the complex is overgrazing by deer and elk. Wolves and cougars once kept their populations in check, but now the herds of these herbivores are larger. Additionally, animals often take shelter in Pando to avoid hunters.

The animals eat the tips of new stems, leading to plant death and restricted growth. This problem does not exist in the fenced area of the ecosystem. Decades ago, humans excluded moose and deer from a small area, allowing the organism to regenerate - the dense plant growth here is referred to as a "bamboo garden."

Elk and deer are not the only threats to Pando. Older stems are also attacked by at least three diseases: sooty bark canker, leaf spot, and conk fungus.

Although plant diseases have been present and evolving in aspen stands for centuries, their long-term impact on the ecosystem remains unknown. In particular, the lack of new shoots and a growing list of threats to this clonal giant raise serious concerns about its future.

The most serious threat, however, is climate change. Pando originated after the end of the last ice age and has since struggled with a largely stable climate. Climate changes threaten the size and longevity of the tree, as well as the entire ecosystem in which it lives.

While no specific studies on Pando have been conducted yet, quaking aspens are threatened by climate changes such as reduced water resources and warmer springs, which hinder the production of new leaves. As competition for dwindling water resources increases, along with predictions of record summer temperatures and the risk of more intense wildfires, Pando will have difficulty adapting to rapidly changing conditions and maintaining its size.

Pando, the world's largest scientifically documented organism, has proven resilient to the environmental changes that have occurred since European settlement in the 19th century and increased recreational activity in the 20th century. It has dealt with diseases, fires, and grazing, and despite concerns about its future, scientists continue to discover the secrets of its resilience. The Forest Service is working to protect Pando and its ecosystem.