Aspens - Colonies of Clones, Families of Fabulous Color
Durango Herald, Sept 14, 2006
Allison Pease, Executive Director

Aspens leaves showing shades of color.

Over the next few weeks, the mountains around Durango will take on a shimmering glow as aspen trees mark the passage of autumn.

Sometimes rich in hearty reds, sometimes emboldened in brilliant gold, these quaking groves will vary in color from place to place.

The variety of color is explained by the unique way aspens reproduce. Aspen groves are colonies of clones, families of color.

With a broader range than any other North American tree, aspens are found from Newfoundland to Alaska to central Mexico. In the East, aspens are one of hundreds of native tree species, but in the arid West, they are one of only a few species that thrive. Some Colorado forests contain as much as 35 percent aspen, and the groves are considered second only to riparian zones in the quality of habitat they provide.

The trees produce two-inch catkin flowers in early spring. These catkins have small (one-quarter-inch) narrow cones that release tiny, cottony seeds. While a mature tree can produce 1.6 million seeds annually, germination is difficult. Seeds are viable only for short periods and require a continuous supply of moisture, exposed mineral-rich soil and the right temperature - typically between 59 to 77 degrees F.

As a result, aspens in the West reproduce almost entirely by ramets (sprouted clones) that sprout from existing root systems. They grow in stands of a single male or female plant.

While individual aspen ramets are among the shortest-lived trees in the forest, aspen colonies can be extremely long-lived organisms. Discovered in 1992 by researchers from the University of Colorado at Boulder, the Pando (Latin meaning "I spread") colony in Utah is a massive grove of aspen trees that is actually a single remarkable plant. Originating from the root system of a single tree, this incredible organism is estimated to weigh 6,600 tons, cover 107 acres, contain 47,000 stems and be 80,000 years old.

This characteristic of aspens, to send out cloned sprouts, makes them vital in the recovery of disturbed areas like those affected by fire. Mature root systems can generate 400,000 to 1 million shoots per acre. Young sprouts can grow three feet per year, easily out-competing species that propagate by seed.

However, as shade from a maturing canopy increases, the sprouts decrease. Over time, the conifers grow taller than the aspens, eventually shading them out and taking hold. Thus, aspen clones depend on periodic disturbances such as fire to maintain the colony.

This unique characteristic of aspens also makes viewing their brilliant autumn show even more fun. Different colonies change at different times and with distinctly different colors. So, as you watch the show over the next month, see if you can spot these families of color in individual colonies of clones.