Science Series: Aspens

History of the Aspens

In the Colorado Rockies

October 3, 2023

Aspens near Steamboat Springs, Colorado. Author’s photo

HISTORY OF THE ASPENS

This week, I had the pleasure of driving through the high country of the Colorado Rockies. I live at 6500 feet elevation, so “high country” means about another 3000 feet or more above me. Every year about this time, Fall is ushered in by a flush of Aspen trees as their leaves turn to gold. The particular aspen is called the “trembling” or quaking aspen. The broadleaf and 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, golds, and reds.

Late changing aspen, 6500 feet. Author’s photo

The color change occurs first at the highest altitudes. For example, at 9,800 feet, the aspens “peaked” their color change, and the leaves began to fall this year in September. Where I live, the edges of the aspen leaves are just starting to turn from green to gold. At this time of the year, chlorophyll production, 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.

Aspens: 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. For example, in my yard, 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 must be pulled out.

In the Colorado Rockies, snow may come before the aspens change. If the first snowfall of the year comes before the first day of Fall, the fragile leaves may die before they turn gold. Other times the first snow comes after the change. One might see snow and golden leaves on the ground simultaneously.

In the Roots of Aspens

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. They rarely last more than 25–40 years in urban settings, and half a dozen have died on my property while I’ve lived there for over three decades. However, in forests at higher elevations, they may live almost ten times that length, and the root system may live longer still.

Spreading Aspens

Many colonies grow larger from year to year, spreading over acres of land. In Utah, the oldest known colony, named Pando (“I spread”), is reported to be thousands of years old. Fishlake National Forest, on the western side of the Rocky Mountains, has one of the largest organisms in the world in terms of both volume and mass, measuring 107 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 billpetro.com

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