The Alaska Vegetation Classification - Alaska Geobotany Center ...

Closely related types-Black cottonwood forests are closely related to balsampoplar forests, and the trees themselves are sometimes considered conspecific. Theseed capsules of black cottonwood split into three parts at maturity, as opposed tothose of balsam poplar which split into two parts at maturity. Closed black cottonwoodcommunities resemble open black cottonwood communities in species compositionbut have much greater tree cover.Primary references-US. Department of Agriculture 1986, Viereck and Little 1972.Communities-Populus trichocarpa (undescribed).I.B. I.C. Closed Balsam Poplar ForestDescrlptlon-These forests are dominated by balsam poplar and have more than60 percent canopy cover (fig. 25). This species commonly reaches diameters of40 centimeters (16 in) and heights 01 30 meters (90 ft). Flood-plain balsam poplarstands are the most productive lorest stands in interior Alaska. Annual tree productionaverages 551 grams per square meter per year (4,900 Ib/acre) and reaches950 grams per square meter per year (8.500 Ib/acre) on the most productive sites.Young stands have densities on the order of 2,000 stems per hectare (800 stems/acre), but densities drop to 600 to 800 stems per hectare (200 to 300 stems/acre)in older stands.Alms crispa and A. tenuifolia are common shrubs in these stands. Willows arecommon to abundant in young stands, but drop out after the balsam poplar canopybegins to close. Other common shrubs include Rosa acicularis (which may form anearly continuous layer about 1.5 meters [5 R] high), Viburnum edule, and sometimesCornus stolonifera. Dwarf shrubs are absent. A dense layer of herbs usuallyis dominated by Calamagrosfis canadensis and Equisetum spp. Other common herbsinclude Geocaulon lividum, Galium boreale, and Meffensia paniculafa. Mosses andlichens usually are sparse because they are intolerant of the heavy leaf fall andfrequent flooding that the forest floor is subject to. Some mosses usually are present,though, on the bases of the tree trunks, and the lichens Pelfigera spp. and Cladoniaspp. can be found on sites flooded relatively infrequently.Phases-South of the Alaska Range, Oplopanax horridus may dominate the herblayer and a variety of ferns becomes important.Figure 2SClosed broadleaf forest of balsampoplar with a shrub layer of Ainus tenuifolia, Rosaadcularis, and Viburnum wduie and a herbaceouslayer primarily of Equisetum awense and E.prarense on the flood plain of a river in interiorAlas!ia