Trees are known for their longevity, and there are countless examples of trees living to 1000 years and beyond. At this age they can grow to cover acres of land, but in Southern Utah, USA, the Pando aspen tree colony breaks all records.
The unusual properties of aspen trees
Aspen trees are curious. Although they are the most widespread variety of tree in North America, some argue that they shouldn’t be thought about like other trees. Above ground, they look very similar to birch trees, with smooth white bark pockmarked with black scars from fallen lower branches. Despite the apparent similarities, Populus tremuloides or quaking aspen trees couldn’t be more different.
The real magic takes place underground. Like the mychorhizal networks that link individual trees in a forest, an extensive network of roots grows underneath the trees, connecting them. Unlike the fungal networks, however, all of the trees are part of the same organism, growing from the same set of roots. In this way, one aspen ‘tree’ can have thousands of trunks, all genetically identical.
This method of asexual reproduction gives the aspen some incredible properties. One colony of aspens will change color in the autumn at the same time, but the group right next to them won’t have started the process. The result creates spectacular pockets of color that cover the landscape in autumn.
Aspen colonies are also very resilient. Thanks to their deep, strong roots, they can quickly regrow after forest fires and other calamities. In fact, recent efforts to prevent forest fires have had the unexpected consequence of reducing aspen populations, as taller trees like spruces and firs crowd them out. Not to worry though, as aspen colonies can regrow from their root systems even after lying dormant for over a hundred years.
The current best practice to encourage regeneration is a bit counter-intuitive: clear cut a large section of the forest. Aspens will be the first to regrow, and aren’t even slowed by cold weather, since they have a layer underneath their bark that is able to photosynthesize and create sugars. This means it can continue to grow even after it and other deciduous trees have lost their leaves.
The oldest and heaviest living thing on Earth
When Burton V. Barnes was exploring the forests of the Fishlake National Forest in Utah, he made an amazing discovery. A single aspen colony consisting of 50,000 individual trunks extended more than a hundred acres. It was eventually called ‘Pando’, meaning ‘I spread’ in Latin. It’s also called ‘The Trembling Giant’.
Researchers are unsure about the actual age of Pando, but the general consensus is 80,000 years, with some estimates as high as 1 million years. For reference, even the conservative estimate of 80,000 years dates it back to the start of the most recent ice age. It would be at least 50,000 years old before humans set foot in North America. This makes it much older than any other tree, and by most accounts it’s the oldest living thing on the planet.
The individual trunks of Pando average a respectable 130 years, but they regularly die and are replaced by a new, identical clone.
In addition to its age, Pando is also known for its weight. At an estimated 6,000 metric tons, it’s the heaviest living thing on Earth. It was celebrated as one of the 40 ‘Wonders of America’ in 2006, with its very own commemorative stamp from the United States Post Office.
How Pando grew so old
The reasons for Pando’s unique longevity lie in the history of its geographical region. Although they favor asexual reproduction (as in clones), aspens are also capable of flowering to create new offspring. This normally happens in wetter regions, which is why the aspen trees in New England are much younger and more genetically diverse.
In the Western United States, climate changes dating back more than 10,000 years have made the region much more arid than in the past. Young aspen trees will not thrive in these conditions, so the existing colonies favored clonal reproduction. After a certain point, the root systems become so deep and complex that they can sustain growth indefinitely.
Many of the oldest trees in the world are threatened by invaders, whether they’re insects, diseases, or other plants. Aspens seem to be immune to these threats. Even if an individual trunk or thousands of trunks die from infection or fire, the roots remain unaffected.
Recently, Pando hasn’t been regenerating as well as rangers expect. No one is sure why, but special care is being taken to make sure that it continues to thrive for future generations. One thing is for certain, Pando may be the oldest living thing in the world, but it certainly hasn’t grown frail in its old age.
Many people have commented about the beautiful photos used in this article. Most of them can be found on the US Department of Agriculture Forest Service page. Not only do they protect the forest, they also have some excellent photographers.
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