Tremble and Quake

I often hear the statement, “Aspen don’t live very long,” when having discussions about trees on the Front Range, especially when people have an opportunity to plant a new tree. The notion that aspen are a short-lived tree sparks a number of thoughts and questions and really a curiosity about these organisms many people regard as short-lived.

If you happen to be a tree geek (aka arborist), you probably know that the oldest and largest recognized single living organism on this planet is a colony of aspen in Utah. It even has a name, Pando, given by Michael Grant of the University of Colorado. Pando spans over 106 acres, with over 50,000 stems and an estimated 6,600 tons of mass - a genetic individual referred to as a clone.

When most of us think of trees we think of massive stems growing out of the ground high into the sky with leaves or needles. This is the predominant visual manifestation of trees, but when it comes to the oldest trees and Pando it is actually the roots that live the longest. These root systems live on, long after the initial stem has decomposed and returned to the earth. The root system of Pando is thought to be at least 80,000 years old with some scientists postulating that it’s likely to be one million years old.

When an aspen stem begins to dieback the root system will often send up a sprout from one of it’s lateral roots. This sprout or “sucker” is genetically the same tree and will grow more rapidly than a seedling if given the right conditions. This growth is because it is able to draw on larger energy stores than seedlings. Suckering is how Pando has survived for millenia. This suckering is also what many people experience popping up in their lawns each year, much to their frustration. Humans have not yet learned a way to effectively tell aspen how annoying this is and to please stop.

Aspen stems can grow quickly and can also dieback at a relatively young age. The growth rate of aspen is typically higher in cool, moist and sheltered conditions. The growth of these trees slows with exposure to wind, higher elevation and more arid conditions. It’s these arid conditions that favor the clonal reproduction of aspen especially in the West. Pando hasn’t reproduced sexually for about 10,000 years, since the last glaciation. Now that’s a long time.

In recent times it has been observed that Pando may be declining and dying. The reasons for this are complex and have to do with pressure from animal grazing and climate change. The young suckers are being eaten at a fast rate, preventing the organism from being rejuvenated. Their vigorous stems cannot grow up to replace the older mature stems. This means Pando does not have a healthy canopy of various aged stems. The future of Pando’s survival depends upon the survival of these young stems. The need to protect and care for the next generation is a lesson we can all learn from.