Every year about this time, Fall is ushered in by a flush of Aspen trees as their leaves turn to gold. Where I live in the Rocky Mountains of Colorado, the particular aspen is called the trembling or quaking aspen. The broad leaf and the flattened stem cause them to flutter in the breeze. It is a type of poplar tree called populus tremuloides. As tourists visit New England in Autumn for Leaves and Lobsters,visitors come to Colorado to leaf peep as the aspens change to dramatic yellows and reds. I did so recently along the Continental Divide.
The change in color occurs first at the highest altitudes. For example, at 9800 feet, the aspens “peaked” their color change and the leaves begin to fall at the end of September. Where I live at 6500 feet, the edges of the aspen leaves are just beginning to turn from green to gold. At this time of the year, the production of chlorophyll which gives the leaf its green pigment slows to a standstill and the yellow, orange and red pigments of carotenoids and anthocyanins show in the leaf.
Send in the Clones
Aspens are unusual in that they grow in large communal groves or more specifically clonal colonies. These form from a single seedling. They spread widely across the area by roots that erupt above ground as root suckers. In my yard, for example, they can spread dozens of feet, invariably coming up in the middle of my lawn. Initially looking like weeds, they are not killed by traditional weed killers but need to be pulled out.
In the Colorado Rockies, snow may come before the aspens change. Several years ago the first snowfall of the year came the last day of Summer. When that occurs, the fragile leaves may die before they turn gold. Other times the first snow comes after the change. One might see snow and the golden leaves on the ground at the same time.
In the Roots
An aspen tree may die, but the root system remains intact, sending up replacements nearby. In this way, a grove may survive a large forest fire and is very hardy. The trees themselves are subject to a variety of diseases and insects. In urban settings, they rarely last more than 25–40 years, and half a dozen of them have died on my property. However, in forests, they may live almost 10 times that length, and the root system longer still.
Many colonies grow larger from year to year, spreading over acres of land. In Utah, the oldest known colony, named Pando (“I spread”) is reportedly thousands of years old. On the other side of the Rocky Mountains from me, it is located in Fishlake National Forest and is also considered the largest organism in the world in terms of both volume and mass, measuring 106 acres and 6,000 tons.
For you shall go out in joy and be led forth in peace; the mountains and the hills before you shall break forth into singing, and all the trees of the field shall clap their hands. -Isaiah 55:12
Bill Petro, your friendly neighborhood historian
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