Quaking Aspens

Contributed by Lois Ports for Bristlecone Audubon

Aspens (Populus tremuloides) are the most widespread tree in North America. From the Midwest, across Canada, north into Alaska and across the West through to Arizona and New Mexico, quaking aspens occur on the edge of conifer forests in clusters or “clones.”

One aspen tree is actually only a small part of a larger organism. A stand or group of aspen trees is considered a singular organism with the main life force underground in the extensive root system. Before a single aspen trunk appears above the surface, the root system may lie dormant for many years until the conditions are just right. In a single stand, each tree is a genetic replicate of the other, thus a “clone” of aspens is used to describe a stand. Each aspen grove includes one or more aspen clones. Take a drive up Lamoille Canyon during the fall and it is easy to see where the different clones are located. The aspen trees of a particular clone will change color at the same time because they are genetically related.

Older than Sequoias or Bristlecone Pines, the oldest known aspen clone has lived more than 80,000 years on Utah’s Fishlake National Forest. Not only is that clone the oldest living organism it is also the heaviest, weighing in at an estimated 6,600 tons. Even if the trees of a stand are wiped out, it is very difficult to permanently extinguish an aspen’s root system due to the rapid rate in which it reproduces.

The deciduous aspen stands thrive in a variety of environments. Aspens quickly colonize recently burned or bare areas to establish a stand of young trees given the proper conditions. They prefer moist soil but can survive near springs in desert conditions. One vital variable for a healthy clone is abundant sunshine. Aspens grow all the time—even in winter. Beneath the thin, white outer bark layer is a thin green photosynthetic layer that allows the tree to create sugars and grow when other deciduous trees would otherwise be dormant. During hard winters, the green, sugary layer provides necessary nutrients for deer and elk. Throughout the year, young aspens provide food or a variety of animals including beaver, porcupine, grouse and rodents. 

Today, many places in the West have seen diebacks of aspen. This may be due to several different factors, such as climate change, which exacerbates drought and modifies precipitation patterns. Sudden aspen death is occurring more often as a result of drought stress. In areas where grass is limited, deer and other ungulates are heavily feeding on young aspens, preventing the trees and clone from reaching maturity. Additionally, successional replacement by conifers due to fire suppression alters forest diversity and creates conditions where aspen may be at less of an advantage. Aspens do not thrive in the shade, and it is difficult for seedlings to grow in an already mature aspen stand. Fire indirectly benefits aspen trees, since it allows the saplings to flourish in open sunlight in the burned landscape, devoid of other competing tree species. 

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