Cottonwood and Balsam Poplar
It is common for people in interior Alaska and corresponding areas of northwestern Canada to use the name cottonwood when referring to one widespread variety of deciduous tree. But since cottonwoods do not grow in Alaska except on the southern and southeastern coast, the terminology obviously is wrong.
The error is a small one in one sense because the tree referred to, balsam poplar, is practically indistinguishable from its close relative, the black cottonwood. Balsam poplar is the most widespread broadleaf tree in Alaska; it ranges even farther north and west than another close relative, the quaking aspen.
Close up, it is easy to distinguish between balsam poplar and quaking aspen from the leaves and, to a lesser extent, by the branching structure. Where they appear in mixed stands, the poplar sometimes has small, leafed branches lower down on the trunk. Aspen leaves are nearly round, one to two inches across, shiny green above and pale beneath. Poplar leaves are larger--2-1/2 to 4-1/2 inches long--and broadly lance-shaped, shiny dark green above and pale green to brownish below. The cottonwood leaf is very similar to the poplar.
If you see a cottonwood tree in interior Alaska, you can be sure it's a balsam poplar, but in southern Alaska it could be either. In areas such as the lower Susitna Valley, near Anchorage, the trees themselves apparently do not know the difference, because they interbreed to produce hybrids. Once in a great while, a poplar goes out on a limb and even hybridizes with an aspen. Only the experts can identify the end product.
Both poplar and cottonwood grow well in river bottoms and sand bars. While poplar may grow to 100 feet high and two feet across, cottonwood can reach to 125 feet and be much larger in diameter. Cottonwoods three feet in diameter at breast height are common. To avoid both bending over and the flare near the tree stumps, foresters measure the tree diameters at breast height, hence the term breast height diameter.
One giant cottonwood near Klukwan, not far from Skagway and Haines, has breast height diameter just over ten feet. The Klukwan giant holds the national record for black cottonwood diameter. Its nearest rival, a tree near Salem, Oregon, does hold the national height record. The Klukwan giant belies the belief that trees tend to get smaller the farther north one goes.
Both balsam poplar and cottonwood have value for fuel wood, pulp and lumber. The large cottonwood stands in the lower Susitna Valley are considered to have the highest potential for economic development of any stands in the valley, though the volume of both white spruce and birch there is somewhat larger. The best cottonwood stands in the Susitna Valley contain as much as 34,000 board feet of lumber per acre. Whereas balsam poplar has somewhat limited use for lumber, black cottonwood has higher strength and is, therefore, superior.
Persons wishing to learn more about Alaska's trees will be interested in a low-cost but comprehensive book by Leslie A. Viereck and Elbert L. Little, Jr. entitled Alaska Trees and Shrubs. It is published by the U.S. Department of Agriculture.
