Aspens can be identified by their smooth, white bark marked by black scars where lower branches are naturally self-pruned. Quaking Aspen leaves are somewhat heart shaped, with finely saw-toothed margins and range in size from 1.25-3" (3-8 cm) long. The leaves attach to branches via a long and flattened petiole, so that even the slightest breeze causes the leaves to flutter. This gives the overall tree the appearance that it is quaking or trembling - hence the common name Quaking Aspen and the scientific name's specific epithet - tremuloides. In the spring and summer, leaves are glossy green on the upper surface and dull green underneath. In the fall leaves turn yellow, gold, and in rare instances, even red. Quaking Aspens grow in large and dense colonies throughout North America enduring lows of -78° F and highs of 110° F. They prefer moist soil, but can grow near intermittent springs in desert environments that receive less then 7 inches of annual precipitation. The only absolute requirement for Quaking Aspen is lots of sunlight.
Quaking Aspens are often confused with birch trees. Although aspen are somewhat similar in appearance to some species of birch, birch trees belong to an entirely different family of trees. Birch are famous for having bark that peels back like paper; aspen bark does not peel. Whereas aspen leaves are perfectly flat, birch leaves are slightly "V" shaped and more elongated than Quaking Aspen leaves.
Common Names: Quaking Aspen, Trembling Aspen, "Quakies"
Scientific Name: Populus tremuloides
Size (height) English & Metric: 40-100 ft (12-30 m) tall
Habitat: Moist soils in openings or along edges of pine and spruce/fir forests
Flowering Season: May & June but rarely flowers
Range: From New England through Canada, into Alaska, and south into California, Arizona and New Mexico.
Aspen are remarkable and unique trees. In fact they are so different that it may be better not to think of aspens as trees. First of all, a stand of aspen is really only one huge organism where the main life force is underground. Think of aspens as large 1-20 acre systems of roots that remain hidden underground until there's enough sunlight. Then the roots sprout up white things called trunks that then leaf off green things called leaves. This is called "vegetative" or asexual reproduction. Only after severe fire and under ideal climatic conditions, will aspen reproduce sexually as a flowering plant.
With careful inspection, clones can be mapped, as all the trees that sprout from a single clone will have the same branching structure because they are genetically identical to one another. Even easier and more obvious is to watch as aspen forests change color in the fall. Members of different clones will all have the same shade of color transitioning from green to yellow at the same time. By examining this different color patchwork along a mountainside you can distinguish individual clones from each other.
Asexual or vegetative reproduction from root systems offers many benefits including phenomenal longevity. Aspen "clones," as the individual root systems are called, can live to be thousands of years old. The oldest known clone in existence is called "Pando" and is located in the Fishlake National Forest north of Bryce Canyon National Park in central Utah. It has been aged at 80,000 years! Although 5-10,000 year-old clones are much more common, even these youngsters are much older than Sequoias and even Bristlecone Pines. Current research on fungal mats in Oregon and Creosote Bushes in the Desert Southwest may rival aspen for the title of "Oldest-known Living Thing."
The other aspect of their lifestyle that makes them unique is that beneath the thin white outer bark is a thin photosynthetic green layer that allows the plant to synthesize sugars and keep growing even during the winter when all other deciduous trees go into dormancy. This green layer of the bark makes it survival food for deer and elk during hard winters.
Because of their vegetative reproduction, aspens are in no danger of going extinct. Aspen forests will eventually become spruce and fir forests as the taller, more dense trees shade out the aspen underneath the canopy. However, even after 100 years or more, the dormant root system will spring back to life sprouting new trees once sunlight is allowed to reach the forest floor again. Therefore, forest fires, no matter how severe, encourage the growth of new aspen trunks in the asexual process also known as "root suckering."
Aspens are so successful that curious foresters have tried everything in an effort to determine what it takes to kill an aspen clone. The only sure method is injecting tons of herbicides directly into the root system. Even "discing" (a huge roto-tiller pulled by bulldozers) down to three feet below the soil will not kill an aspen clone. The chopped up roots keep right on growing. Heavy browsing by deer and elk is hypothesized to be detrimental to aspens, but in reality, only kills individual trees. Individual trunks invariably become afflicted with disease after 100 years or more, but the root systems are apparently immune. The only natural force that appears to limit growth of aspen are pocket gophers, which in abundance, can chew aspen root systems back faster than they can grow.
When and where to see at Bryce:
The above-ground portions of Quaking Aspens are few and far between at Bryce Canyon National Park. Historic photographs show that these kinds of forest used to be much more common. The aggressive suppression of forest fires, (natural or otherwise) has allowed spruce and fir forests to overshadow the once common aspen groves. Using prescribed fires to burn away key portions of the spruce and fir forests will allow aspen to quickly return to their former glory as a keystone species that assures the survival of many other kinds of plants and animals. Look for little pockets of aspen along the scenic drive at the southern end of the park and also tucked underneath the canyon rim between Sunset and Sunrise Points.
Buchanan, Hayle 1992. Wildflowers of Southwestern Utah. Bryce Canyon Natural History Association. Bryce Canyon, Utah
Lanner, Ron. & Rasmuss, Christine. 1988. Trees of the Great Basin: a Natural History. University of Nevada Press
Little, Elbert L. 2001 National Audubon Society Field Guide to Trees - Western Region. Random House Inc. New York, NY
Stuckey, Martha & Palmer, George. 1998. Western Trees: A Field Guide. Falcon Publishing, Inc. Helena, MT