Habitat: Western Slope Montane and Subalpine, Eastern Slope south of Crowsnest Pass
Height: Up to 40 m
Description: As you cross the continental divide towards British Columbia, or head south towards the Crowsnest Pass and the U.S. Rockies, the balsam poplar slowly gives way to the black cottonwood. Technically, the cottonwood is considered a subspecies of balsam poplar, and like its relative, it prefers low lying moist habitats, often along river courses. It is the largest of the poplar species in the Rockies, often reaching heights of 40 m (130 ft).
Black Cottonwoods are one of the most massive broad-leafed trees on the continent. The large leaves are egg-shaped, almost as wide as they are long, and rapidly taper to a point. They range in size from 7-13 cm (3-5 in), and are dark green above, and silvery-green below. Like the balsam poplar, they also exhibit brown resin blotches on the lower surface. The bark on young trees is a yellowish-green colour, becoming gray and furrowed on older trees. It is the most important deciduous tree in B.C., and is heavily logged.
Similar Species: The black cottonwood is most often confused with the balsam poplar, and is technically only a subspecies of the poplar. The leaves of the balsam poplar are more elongate, and are usually much longer than they are wide. For a more technical difference, the catkins of the cottonwood split into three parts while those of the poplar split into two.
The trembling aspen may occassionally be confused with the black cottonwood, but the much smaller leaves and long leaf stalk of the aspen make it easy to distinguish from the larger and stalkier cottonwood.
Range: The black cottonwood is common on the western slopes of the Canadian Rockies, but on the eastern slopes is generally found south of the Crowsnest Pass. In the American Rockies, the black cottonwood extends south to Colorado.
West of the Continental Divide, the cottonwood grows in a wide variety of habitats, but in the drier eastern slopes, they are restricted to moist river valleys and lakeshores.
Because of its need for high quantities of water, engineers can use it as an indicator of areas that may be prone to flooding.
Notes: The cottonwood is unmatched in its ability to produce immense amounts of cotton. Each strand has a tiny seed attached. When the cotton is released, cottonwood forests can be ankle deep in this fluff, making this a difficult time for allergy sufferers.
The wide canopies are popular for nesting eagles, hawks and even the rookeries of great-blue herons. Their rotting trunks invite woodpeckers to bore the round holes so critical for the nests of many local songbirds.
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