The Alaska Vegetation Classification - Alaska Geobotany Center ...

Figure 37-A. Aerial view of closed tall shrub of willow and alder surrounded by a mixed birch-sprucestand adjacent to a small stream in south-central Alaska. 8. Ground view 01 dosed tall shrub shown in A.11.8.1. Closed Tall ScrubClosed tall scrub communities have 75 percent or more cover of shrubs 1.5 meters(5 ft) tall or taller (fig. 37, A and 6). Tree species overtopping the shrub canopyprovide less than 10 percent cover. Seedlings and saplings of tree species may beabsent or abundant beneath the shrub canopy. Low shrubs and dwarf shrubs areusually sparse or absent. Mosses may be abundant.II.B.1.a. Closed Tall Willow ShfubDescription-These stands have about 75 percent or greater cover of shrubs (principallywillows) taller than 1.5 meters (5 ft) (fig. 38). Maximum heights range from 2to 3 meters (6 to 10 ft) in the north to over 6 meters (20 ff) in well-developed thicketsin the south. Common dominant species include Salix alaxensis, S. arbusculoides,S. planifolia, and S. lanafa, as well as S. barclayiand S. sifchensis in the southernpart of the State. Sometimes a few alders (Alnus spp.) contribute to the overstorycanopy, and scattered balsam poplar (Populus balsamifera) or black cottonwood(Populus frichocarpa) overtop the willows. Low shrubs such as Pofenfilla fruficosa,Salix hasfafa, and S. brachycarpa are usually uncommon and restricted to openings.The understory is sparse in dense stands, though mosses, including Po/yfrichumspp., Hylocomium splendens, and Drepanocladus uncinatus, may grow abundantly.Slightly more open stands may have a dense understory of Calamagrosfiscanadensis, Fesfuca alfaica, and Equisetum spp.Dlstribution and site characteristics-Closed stands of tall willow are commonthroughout the State except for the Aleutian Islands and a narrow strip of tundranext to the Arctic Ocean. They are especially common in south-central, western,and interior Alaska and occur primarily on flood plains and streambanks, but theyalso are common on roadsides, burns, alpine drainageways, and (especially inwestern Alaska) sheltered slopes and lake margins. Soils usually are well to moderatelydrained and range in texture from loam to gravel. Permafrost is absent or50 centimeters (20 in) or more below the surface.Successional status-Closed tall willow communities on flood plains are successional,usually developing from seral herb communities and eventually replaced bysome kind of forest. Tall willow communities developing on burns usually arereplaced by forests in the forested parts of the State. In tundra regions, closed tall