Quaking aspen, Populus tremuloides, is perhaps the most widely recognized of western trees. It is a characteristic constituent of the Rocky Mountains flora. The species name tremuloides describes the propensity for the leaves to flutter with the slightest air currents because of particularly thin, flattened, pliable leafstalks. In this respect, the western aspen is similar to a Eurasian counterpart, Populus tremula, which is prevalent throughout Britain to North Africa and Asia. The range of P. tremuloides is from Labrador and Hudson Bay to Alaska, southward throughout Canada and the majority of the United States (with the exception of the Atlantic southeast and Gulf Coast) into northern Mexico. There are five subspecies, with variation in flowers, shape and size of the leaves, and autumnal color. Two are primarily eastern, with the major western variety called P. tremuloides aurea, because of the yellow golden fall color. The western variety ranges from Alaska to Mexico, from the Pacific coast to western Texas, Colorado, Nebraska, and Manitoba. The remaining two varieties have limited distribution in Wyoming and Vancouver, British Columbia. Another native is bigtooth aspen, Populus grandidentata, which is found across the Great Lakes region to New Brunswick and Nova Scotia. It has a larger Leaf with more prominent saw-toothing.
In the northern portion of its range, aspen grows from sea level up to 3,500 feet. In the southern aspect of its range, in the Rockies, it is found predominantly between 6,000 and 11,000 feet above sea level. Western aspen is a forest-forming tree, covering large areas with dense, pure stands. It is frequently a temporary forest occupant, but it may be dominant for a long time after fire destruction of conifers. In rich loam soil the trees may grow to 90 to 100 feet high with 30-inch diameter trunks; when cultivated, aspen seldom achieves half that height. It is a good foliage source for livestock such as cattle and sheep, but also for deer and elk.
Aspen propagates both by seedlings and suckering (or cloning), the latter being quite extensive. Many forest groves are derived from a single tree, with new trees arising from numerous sprouts from the shallow root system. At one point in 1990, the largest living organism was felt to be an aspen grove covering 200 acres in Utah, and weighing approximately 6,600 tons. It was found to be a single genetically pure organism. There is little genetic diversity even with seedling propagation, as was demonstrated with regeneration of aspens via seedlings after the disastrous Yellowstone fire in 1988. Distantly related populations shared 90% of the same.
RICHARD W. WEBER, M.D
Ann Allergy Asthma Immunol 2001