Aspen trees are the most widely distributed tree in all of North America. They can be found from Alaska through Canada into the continental United States south and into Mexico. Colorado and Utah (the Rocky Mountains) are home to the largest portions of aspen trees in the world.
Aspen trees are a part of the willow family. There are six species: Big Tooth Aspen; Quaking, Trembling or American Aspen; Common, Swedish, Trembling or Eurasian Aspen; Grey Poplar; Japanese Aspen; Chinese Aspen; and White Poplar.
Aspen trees live in the wild for approximately 120 years. Taller aspen trees provide shade for young spruce and fir trees below and are an important part of the ecosystem. They provide habitat for woodpeckers, bluebirds, swallows, and other species of animals. Fallen aspen leaves, bark and other parts of the tree provide environment for insects, bacteria and fungi. Deer are attracted to aspen trees and the bark as well.
Aspen trees usually reach 20 to 50 feet tall, with a spread of 10 to 30 feet wide.
Aspen leaves change color seasonally, usually a brilliant yellow color, and they are nearly round in shape. The leaves quiver in the breeze and can twist and shake due to flattened petioles. This can also allow greater photosynthesis to occur by factoring in more light during the day. Aspen trees are known for their shivering or quaking leaves in nature.
Legend has it that the crucifix that Jesus Christ died upon was made from an aspen tree. The tree was filled with grief and remorse after Jesus died, and all aspen trees have trembled and quivered ever since. Aspen trees are the only trees that are said to tremble but never bend at the strongest of winds.
Aspen trees are grown in colonies derived from a particular seedling. One colony in Utah is approximately 80,000 years old, possibly the oldest living colony.
According to Northern Arizona University, aspen trees are in decline on the Colorado Plateau. The U.S. Forest Service estimates between 1962 and 1986, aspen trees have declined by 46 percent in Arizona and New Mexico. That is due to the combination of modern fire suppression methods and a steady increase in elk herbivory in many forests.
Scientific researchers continue their studies on aspen trees and birch trees, particularly in the Midwest regions, to see how carbon dioxide and greenhouse gases affect forest ecology and diversity in the long term. In one study, forest scientists are researching how quaking aspen, paper birch and sugar maple in Wisconsin will respond to the levels of carbon dioxide and ozone expected in the north by 2050.