Saturday, October 1, 2022

Pando, Earth’s Largest Living Organism, is ‘Breaking Up’ Because of Herbivory and Fencing

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The 43-hectare Pando aspen (Populus tremuloides) clone in Utah, the United States, is thought to be the largest living organism on Earth by dry weight mass.

The Pando aspen clone from a distance (green foreground and middle — not yellow). Image credit: Lance Oditt, Studio 47.60° North.

The Pando aspen clone, also known as the Trembling Giant, is the largest known organism on our planet in terms of dry-weight mass.

This ‘forest of one tree’ has an estimated mass of 5.9 million kg, covers some 43 ha (106 acres) in south-central Utah’s Fishlake National Forest.

It consists of more than 47,000 genetically identical above-ground stems or ‘ramets’ originating from a single underground parent clone.

The clonal colony was first described in the 1970s and was later named ‘Pando’ (Latin: I spread) based on its vegetative reproductive strategy and alleged ancient lineage.

In 2018, Utah State University researchers Paul Rogers and Darren McAvoy completed the first comprehensive evaluation of Pando.

They found that browsing deer — and to a lesser degree cattle — were harming the stand, limiting growth of new aspen suckers and putting an effective expiration date on the colossal plant.

As older trees aged-out, new aspen sprouts weren’t surviving voracious browsers to replace them. Pando was slowly dying.

In response to the threat, managers erected fencing around a section of the stand to keep grazing animals out, creating an experiment of sorts.

Pando aspen clone study site projected over National Agriculture Imagery Program aerial photography backdrop, Utah, the United States; 64 sample plots were randomly distributed across the study area, with near-equal portions located within no fence, 2013 fence, and 2014 fence management regimes; a low-volume paved road bisects the clone; a campground is in the northeast portion and small cabins are located in the northcentral portions of the study area. Image credit: Rogers, doi: 10.1111/csp2.12804.

Dr. Rogers recently returned to evaluate the strategy, and to do a well-check on the overall health of Pando.

“Pando seems to be taking three disparate ecological paths based on how the segments are managed,” he said.

“Around 16% of the stand is adequately fenced to keep out browsing animals; new aspen suckers surviving those first tender years to establish into new trees.”

“But across more than a third of the stand, fencing had fallen into disrepair and was only lately reinforced.”

“Past browsing still has adverse impacts in this section; old and dying trees still outnumbering the young.”

“And the areas that remain unfenced (approximately 50% of the stand) continue to have concentrated levels of deer and cattle consuming the bulk of young sprouts.”

“These hard-hit zones are now shifting ecologically in distinct ways.”

“Mature aspen stems die without being replaced, opening the overstory and allowing more sunlight to consistently reach the forest floor, which alters plant composition.”

“These unfenced areas are experiencing the most rapid aspen decline, while the other fenced areas are taking their own unique courses — in effect, breaking up this unique, historically uniform, forest.”

“The solution to Pando’s survival might not be just more fencing,” the scientist said.

“While unfenced areas are rapidly dying off, fencing alone is encouraging single-aged regeneration in a forest that has sustained itself over the centuries by varying growth.”

“While this may not seem critical, aspen and understory growth patterns at odds from the past are already occurring.”

“I think that if we try to save the organism with fences alone, we’ll find ourselves trying to create something like a zoo in the wild.”

“Although the fencing strategy is well-intentioned, we’ll ultimately need to address the underlying problems of too many browsing deer and cattle on this landscape.”

The study appears in the journal Conservation Science and Practice.


Paul C. Rogers. Pando’s pulse: Vital signs signal need for course correction at world-renowned aspen forest. Conservation Science and Practice, published online September 8, 2022; doi: 10.1111/csp2.12804

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