Habitat: Montane on both sides of Continental Divide
Height: Up to 30 m
Description: More delicate than the balsam poplar, trembling aspen is appropriately named. Its roundish leaves are attached to the twig by a long flat leaf stalk. This allows them to flutter in the slightest breeze. The leaves are light green in colour, almost round, but rapidly taper to a narrow tip. They are rarely longer than 5 cm (2 in). The bark on young trees is greenish-white to white. A white powdery substance is often apparent on the trunk, and acts as a natural sunscreen for the tree.
When September arrives, no other tree in the Rockies is more colourful. The aspen is able to survive at higher elevations than other broad-leafed trees, and in September, entire hillsides explode into yellows, oranges, and ocassionally red.
Similar Species: In the Canadian Rockies, north of the Crowsnest Pass, the trembling aspen is most commonly confused with the balsam poplar. The poplar is larger, with leaves that have a shorter petiole and are also much larger. The leaves of the balsam poplar are much longer than they are wide, unlike the smaller, rounder leaves of the aspen. As you move farther south, another variety of the balsam poplar, the
black cottonwood becomes more prevalent. This large tree has similar looking bark, but the leaves are also much larger than those of the trembling aspen.
Range: This wide ranging tree is found from Alaska and the Yukon, across Canada and south along the Rockies all the way to Mexico. Few trees are as widely ranging as the aspen which can be found from coast to coast in any area with sufficient moisture. Look for aspen along rivers, in moist areas and on the edges of coniferous forests. In the Rockies, they grow higher than other broad-leafed trees, and can be spotted hugging high south-facing hillsides.
Notes: While aspens produce millions of seeds each year, the seeds lack a hard protective covering as well as any food storage. These two things mean that the seeds remain viable for only a few weeks. Few will ever have the chance to take root. How then do aspens reproduce? The short answer is cloning. When a seed manages to take root, it will send out a series of roots, horizontally just beneath the surface. Periodically, these roots will produce a new shoot (known as a sucker) which will sprout to become a new tree. While it may look like there is a large grove of aspen trees, it may actually be a single tree joined by a common root system.
Every spring and every fall, the trees betray this common root system making it a simple matter to pick out which trees share a root system. Since all of the shoots are actually a single tree, all the shoots will come into leaf on the same day. In September, they all turn golden on the same day--and they will all be the exact shade of gold. These clonal groves can be immense, covering 40-50 hectares (100-125 acres).
Beavers: No other animal is as intricately connected to the trembling aspen as the beaver. Aspen is the most preferred food for beavers and they will regularly relocate their lodges when aspen supplies run low. Beavers feed on the leaves and bark, and use the wood for building their dams and lodges. Early trappers were quick to take advantage of the relationship between aspen and beaver, and would seek out aspen stands near watercourses in order to set their traps.
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