Ancient Quaking Aspen Clones

The wildflowers are playing out their last act of the summer here in Colorado and it is just about the time to focus on fall colors. Unlike the Eastern U.S., with its majestic maples and other colorful deciduous trees, here the primary source of fall color is our beloved Quaking Aspen (Populus tremuloides).

The Quaking Aspen is a graceful tree whose leaves dance in the slightest breeze. They are usually found swarming in large groves and at this time of the year their colorful season finale descends from the high altitudes in a glorious display. These swarms turn yellow and red and we Coloradans log on to the local weather to find out where to worship them with our cameras.

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Eldora, Colorado, Aspen Grove, 26 September 2008

There is more to this popular poplar than meets the lens. It turns out that this plant has a very solitary sex life. Here are the facts:

  • Quaking Aspen reproduce primarily through root sprouts, and extensive clonal colonies are common. Each colony is its own clone, and all trees in the clone have identical characteristics to the original mother tree and share a single root structure.
  • A stand of aspen is really only one huge organism. Think of aspens as large systems of roots that remain hidden underground until there's enough sunlight. Then the roots sprout up white things called trunks (or suckers) that then leaf off green things called leaves. This is called "vegetative" or asexual reproduction. This makes the grove hardy and independent of pollinators but it also halts evolutionary progress making adaptation to environmental change impossible.
  • Entire aspen colonies can be lost due to the encroachment of spruce and fir into its ecosystem. Aspen is dependent on fire, avalanche, or other "clearing" disturbances to keep stands open allowing sunlight to permit reproducing from suckers. Grazing and fire suppression are causing loss of aspen habitat.
  • Thanks to a common genetic blueprint, all members of a clone will all have a uniform shade of color transitioning from green to yellow at the same time. By examining the different color patchwork along a mountainside in the fall you can distinguish individual clonal colonies from each other.
  • Dispite their solitary method of reproduction, aspen seeds do exist. They have very specific conditions needed to germinate and under adverse climatic conditions seldom produce aspen seedlings that survive. Aspens here in the Western U.S. have not propagated from seed since the last Ice Age which means that this ancient organism hasn't evolved for over 10,000 years! Will global warming reward or punish this old giant?
  • A group of 47,000 Quaking Aspen clones nicknamed "Pando" in the Wasatch Mountains, Utah (USA) is sometimes considered the world's largest organism by mass, covering 43 hectares (110 acres).