Quaking aspen (Populus tremuloides) is the most widely dispersed tree in North America. It is found growing across the northern regions of the United States and Canada from the Atlantic to the Pacific Oceans. Groves of quaking aspen trees are also found growing in the high mountains of central Mexico, as well as in mountainous regions as far north as the Arctic Circle.
Each autumn, the shortening of the hours of daylight and the return of near freezing weather triggers the breakdown of chlorophyll, the chemical that gives plants their green color. As the green fades, the quaking aspen forests decorate their mountainous landscapes with spectacular displays of shades of yellow with occasional splashes of orange and red.
Quaking aspens, with their tall, straight trunks, stand alongside the endless miles of meandering forest roads like sentinels guarding the entrance into a high-mountain magical kingdom.
And when discovered on a prairie at the base of an ancient volcano, a grove of quaking aspen becomes a palette of golden colors upon one of ol' Jack Frost's magnificent natural autumn portraits.
The name "quaking" comes from the fluttering action of the trees' heart-shaped leaves when blown by the wind. This fluttering action is caused by the flattened petioles of the leaves. (Petioles are the stalks that attach the leaf blade to the stem.) The yellow-green color of the 1.5- to 3-inch (4- to 7.6-centimeter) leaf surface has an underside color of contrasting silver. The edge of each leaf is finely serrated.
Quaking aspen are members of the willow family, Salicaceae. In the western mountains of the United States quaking aspen grow best at the 5,000- to 12,000-foot (1,500- to 3,700-meter) elevation range. Quaking aspen seldom grow below an elevation of 1,500 feet (460 m) due to the mildness of the winter found at this level. They are a short-lived species, having an average lifespan of 75 to 100 years.
Quaking aspen trees generally grow to a height of about 50 feet (15 m) with a spreading crown of 25 feet (7.6 m). Larger species known as "old growth aspen" that measure some 100 feet (30.5 m) tall and 3 feet (1 m) in diameter have been found in the Rocky Mountains of Colorado and New Mexico. They are a fast-growing tree that prefers a moist, slightly acidic soil. Quaking aspen grow best when the summers are relatively dry with abundant sunshine and when winters see heavy snowfall that reinvigorate the forest soil, resulting in rapid spring and summer growth.
The bark of the quaking aspen is unique in its smooth texture and light gray or off-white color. Some refer to the color as greenish-white. Shallow furrows that look like horizontal lines often appear. Old aspen often have bark that has split, leaving furrows that are dark gray. Since quaking aspens self-prune their lower branches, eye-shaped black scars are common on the lower trunk.
There are both male and female aspen trees. During the time that both male and female trees flower, the male anthers and the female stigmas are both reddish in color adding to the unique character of the quaking aspen tree. Seeds are dispersed by the wind and only remain viable for two or three weeks. They require a moist environment and full sunlight to sprout.
But most quaking aspen trees reproduce asexually by producing clones of the original tree from an ever-spreading root network. Groves of quaking aspen are really the stems of one of the Earth's largest living organisms. Thousands of quaking aspen trees that are genetically identical to each other can be joined underground by a single root network that can continue to reproduce and live for hundreds if not thousands of years.
Because of this root suckering method of reproducing, quaking aspens are often the first to re-establish a forest environment after a forest fire or a man-made forest clearing. As the forest of aspens continues to grow, they begin to provide shade for the forest floor which is necessary for new conifers to sprout. Over time a new conifer forest will grow often replacing the aspen stand.
The heartwood of quaking aspen was once considered to be worthless by loggers. The tree even had the nickname "weed tree" in some parts of the mountains. But the modern lumbering industry now sees quaking aspen as "green gold" for its pulp's value for producing high quality paper. Groves of quaking aspens are prime habitat for wildlife and add great beauty to recreational sites.
Fire in the forest is the primary threat to a grove of quaking aspen. Fire easily kills the thin bark of the tree and even a light fire can injure the bark, allowing a decaying fungus to enter. These decaying fungi will soon destroy and hollow out the wood, causing the tree to then break during mountain windstorms.
Insects, animals and humans can also easily damage the bark of quaking aspen allowing for disease organisms to enter. Grazing animals such as herds of deer and elk eating the tender bark can have a devastating affect on a quaking aspen grove.
Botanists speculate the quaking aspen forest of the Rocky Mountains may be in decline. Much of the decline, they believe, is from the normal succession toward a conifer-dominated forest. Yet in the areas of most recent massive wildfires, it will be the quaking aspen tree that begins to sprout first in the blackened landscape in the cycle of re-vegetating the mountain forests.
But, where the forests still stands and are healthy, it is September once again and the golden colors of the quaking aspen are a sure sign that summer is over.
For those who live among the quaking aspen, the firewood has once again been cut and stacked in preparation for the winter that will soon come.
The roads of mountain meadows lead past the split rail fence toward the groves of quaking aspen trees at the base of the silent volcano. And since these quaking aspen groves share a common root system, the leaves turn golden at the same time, creating a brilliant, picturesque landscape.
Autumn is coming to the mountains of the American West once again. How do we know? The beauty of the golden quaking aspen tells us so!