Pando: The largest organism on Earth is dying

One of the largest living organisms on planet Earth is in peril and in need of urgent attention, according to a study by researchers Paul Rogers and Darren McAvoy, from Utah State University, in south-western US. The organism, known as Pando (which means “I spread”, in Latin), is outwardly a forest of quaking aspen trees (Populus tremuloides) occupying 43 hectares in Utah’s Fishlake National Forest. But, in fact, it is an individual comprising about 47,000 genetically identical male aspen ramets, or above-ground stems, and one massive root system weighing about 6 million kilograms.

Rogers and McAvoy say their Pando findings have global implications. Their report, published in the journal PLOS One, says aspen forests, which contain chiefly P. tremuloides and close relative P. tremula, are “among the most widespread tree systems in the world”, but they are threatened by human impacts such as global warming, deforestation, fire suppression, and unchecked herbivore grazing.

“While Pando has likely existed for thousands of years – we have no method of firmly fixing its age – it is now collapsing on our watch,” Rogers says.

The researchers studied various attempts at protecting the organism, including experiments involving clear-cutting portions of the forest and building fences around certain areas.

They concluded that their “first comprehensive assessment of conditions at the famed Pando aspen clone reveals an ancient forest threatened by recent human decisions”, and that “a vital lesson derived from this study is that independently managing vegetation and wildlife may harm both”.

“While several human alterations to this forest have taken place in recent decades, it is the lack of simultaneous herbivore regulation that has caused this stand’s degeneration,” they say.

This unique “forest of one tree” was first described in the 1970s, the report says. A “gross estimate of a post-glaciation origin seems plausible, meaning the clone is likely thousands of years old, though not older than 14,000 years”.

The researchers say the Pando aspen clone is “putatively the largest known organism on earth in terms of dry-weight mass”. However, claims as to the “largest living organism on Earth” have also been made on behalf of an Armillaria solidipes, a specific honey fungus that reportedly measures more than 10 square kilometres in the Blue Mountains of Oregon, on the US west coast.

The paper says systems such as Pando support “unusually high levels of biodiversity, when compared to surrounding conifer-dominated forests”.

In a better-managed setting, aspen forests such as Pando would benefit from “rejuvenating fire”, and the presence of predators that would keep in check native browsing animals.

Although human incursions into the forest have harmed it, the paper says the greatest damage to the Pando organism has been from grazing animals, mainly mule deer (Odocoileus hemionus) and, to a lesser extent, domestic cattle and Rocky Mountain elk (Cervus elaphus).

Rogers and McAvoy say most people are unaware of Pando, but efforts have begun to increase public awareness and education about its significance, while at the same time avoiding an increase in visitor numbers, which could lead to trampling and vegetation damage.

These combined effects can be especially damaging to the forest’s resilience, they add, along with having a “cascading effects on biodiversity”.

To help them achieve a complete measure of the clone forest’s current status, the researchers built a collection of aerial photography of the grove. They gathered aerial photographs covering nine years at the site and digitised six of them, which provided ample material for interpretation.

These photo years (1939, 1950, 1967, 1976, 1989, 2011) were processed so each could be directly compared at the same scale.

They also used previous genetic sampling work to digitise an accurate Pando clone boundary, which gave them a consistent frame for viewing changing forest conditions over a 72-year period.

The researchers say many previous conservation efforts have failed to find coordinated strategies that consider the needs of the forest and the inevitable presence of herbivores, particularly at regional and multinational levels.

“There should be no confusion over the point that both domestic and wild herbivore populations are governed by people’s preferences and actions, and that those decisions result in long-term consequences for ecosystems writ large,” they write.

Rogers says Pando serves as “a symbol of nature-human connectedness and a harbinger of broader species losses”.

“Regionally, and indeed internationally, aspen forests support great biodiversity,” they conclude.

“This work further argues for ‘mega-conservation’ as a departure from traditional individual species-habitat approaches. It would be shame to witness the significant reduction of this iconic forest when reversing this decline is realisable, should we demonstrate the will to do so.”

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