The Alaska Vegetation Classification - Alaska Geobotany Center ...

Dlstrlbutlon and slte characterlstlcs-open aspen stands usually occur on verydry sites on steep, south-facing slopes along rivers in interior and south-centralAlaska. They commonly are associated with dry midgrass-shrub or sagebrush-grasscommunities. Soils generally are shallow silt loams over fractured bedrock and arequite warm and dry. Open aspen stands also infrequently occur on more or lesslevel, well-drained alluvium. If permafrost is present, it will be at depths greater than70 centimeters (28 in).Successlonal status-Open aspen communities frequently develop on sites wherewhite spruce stands have been destroyed by fire. White spruce may be unable toreinvade steeply sloping, dry sites, though small changes in summer climate mayenable such an invasion at some time in the future. A series of hot, dry summersmay stress the aspen to the point of making them susceptible to death by certaindiseases, thus converting the open aspen stands to dry midgrass-shrub communitiesor open sagebrush-grass communities. On the other hand, a series of wet, coolsummers presumably could lead to the expansion of aspen forest at the expense ofgrassland and shrubland.On most flood-plain sites aspen will be replaced by white spruce if left undisturbed.Closely related types-Open aspen communities are similar to closed aspencommunities but have less tree cover and generally occur on steeper and dryerslopes.Photographs-Figure 30, this publication.Primary references-Neiland and Viereck 1977, Viereck and others 1983, Yarie1983.Communltles-Populus tremuloides/Salix spp./Arctosfaphylos uva-ursSramineae(Yarie 1983). Populus fremuloides/Salix spp./Arcfosfaphylos uva-ursEpilobium spp.(Yarie 1983). Populus fremuloides/€laeagnus commufata-Shepherdia canadensis/Arctostaphylos spp./lichens (Neiland and Viereck 1977). Populus fremu/oides/Shepherdia canadensis/Calamagrosfis purpurascens (Viereck and others 1983).I.B.2.c. Open Balsam Poplar (Black Cottonwood) ForestDescrlptlon-These open stands are dominated by balsam poplar or blackcottonwood and have a total tree cover of 25 to 60 percent (fig. 31). Other treespecies generally are absent. Balsam poplar reaches sizes of 40 centimeters (16 in)d.b.h. and 20 to 30 meters (65 to 100 ft) in height. The trees of most open stands,particularly those near timberline, rarely exceed 10 to 12 meters (30 to 40 ft) tall,though the maximum diameters remain about the same. Black cottonwood may growslightly larger than balsam poplar. Understory composition is variable, but thereusually is a scattered tall shrub layer consisting of Salix spp. and Alnus spp. and alow shrub layer dominated by Viburnum edule, Rosa acicularis, Shepherdiacanadensis (restricted to balsam poplar), or Oplopanax horridus (restricted to blackcottonwood). Common herbs are Calamagrostis canadensis, Pyrola spp., Mertensiapaniculata, Epilobium angustifolium, and Arctostaphylos rubra. Hylocomiumsplendens and Pleurozium schreberi are common bryophytes.