Pando, The Trembling Giant

What is the largest living organism? Some would say the elephant, weighing in around 13,000 pounds. Some would say the blue whale, easily weighing over 200,000 pounds. It is difficult to comprehend the immense size of some of the creatures on earth. Today, I want to look at the grove of Trembling aspen trees in Utah. Until recently, it was considered to be the largest living organism in the world (it was displaced by a pretty awesome fungus).

Pando

Taking up approximately 106 acres (43 hectares) and weighing nearly 6,000 metric tons, this grove of aspens is one of the largest living organisms discovered to date. To add to the enormity of it all, there are an estimated 47,000 stems within this 106 acres, all belonging to a singular root system. Estimates of the age of the root system are upwards of 80,000 years old, making it not only one of the largest but also one of the oldest known living organisms.

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

Trembling Aspen

Populus tremuloides, or trembling aspen, is native to North America. It is one of the most aggressive pioneer species around, meaning it is one of the first tree species to colonize open areas (including burned areas). Because it is one of the first trees to grow after forest fires, repeated forest fires have allowed aspen to gradually increase their distribution. Left unchecked however, aspen is easily replaced by other species that are shade tolerant (shade tolerance is the ability for a species to thrive in shaded areas, and tend to replace trees that need direct sunlight by gradually choking them out). Due to regular fires and the substantial size of the root system, Pando has yet to be replaced.

Trembling aspen has the ability to reproduce asexually by sprouting new stems from the existing root system. Every stem that sprouts from the root system is an identical clone of the parent tree, meaning that it is an extent of the same organism. This allows the individual to take over more territory, giving it more nutrients and other resources.

Within the Pando Clone, Fishlake National Forest, Utah. Photo by B. Campbell.

The Problem

If you are anything like me, the vast size of this is mind boggling. Moreover, the Earth itself is mind boggling. This organism has persisted for thousands of years, and in the last few decades, there has not been any notable new growth occurring. In 2018 a study found that this lack of growth is likely due to human interference. Not global warming or anything (although that probably doesn’t help), but the study specifically called people out on allowing deer and other ungulates to thrive. Lack of predators (due to the removal of them) have caused deer populations to skyrocket, leading to them chowing down on new aspen stems, resulting in fewer saplings.

The Takeaway

Honestly, I am not sure if we can fix all of the things we as a species have done to the planet. It is arguable that Pando would eventually stop spreading without our help, but then again, maybe it wouldn’t. 80,000 years is a long time to persist, and we may have inadvertently stunted the growth of this trembling giant. Granted, there have been fences put up around parts of the forest, and there has been some success in these areas, but I feel that anything less than reintroduction of natural predators is a band-aid. Maybe we should build a wall around Pando instead of the southern border.

Anon. Mule deer impede Pando’s recovery: Implications for aspen resilience from a single-genotype forest. Website https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0203619

Anon. How Aspens Grow. Website https://www.fs.fed.us/wildflowers/beauty/aspen/grow.shtml