The Alaska Vegetation Classification - Alaska Geobotany Center ...

Successional status-Communities on alpine and subalpine slopes are probablystable, though possibly subject to slow colonization by forests. Subarctic lowlandstands also may be fairly stable as long as moisture conditions are constant. A dropin the water table probably favors tree invasion, and a rise in the water table mightallow shrub-tussock communities or shrub birch-ericaceous shrub bog communitiesto occupy the site. Arctic stands generally develop from closed shrub thickets as thepermafrost table rises and the active layer becomes wetter. In time, many of thesestands will develop into shrub-tussock tundra.Closely related types-Open low shrub birch-willow shrub is similar to mesic shrubbirch-ericaceous shrub communities and shrub birch-ericaceous shrub bog communitiesbut has more willows, willow being codominant with birch. They also resemblesome open low willow communities but have shrub birch. They are similar to closedlow birch-willow and open tall birch-willow communities but are more open andshorter, respectively. Some stands may approach shrub-tussock bog or shrub-tussocktundra, but Eriophomm vaginatum is much less important than it is in those types.Primary references-Spetzman 1959, Steigers and others 1983, Talbot and others1984, Viereck 1963.Communities-Betula nana-Salix brachycarpa-S. planifolia-S. lanata/Arctostaphylosrubra-Cassiope fetragona-Ledum decumbens (Spetzman 1959). Betula nana-Salix lanata/Carex aquatilis-Equisetum spp. (Craighead and others 1988). Salixarbusculoides-S. glauca-S. hastataBetula glandulosa/Bromus pumpellianus-Festucaaltaica (Batten 1977). Betula glandulosa-Salix glauca-S. planifolia/Festuca alfaica-Vaccinium vitis-idaea-Arctostapaphylos alpina/Hylocornium splendens (Viereck 1963)Salix glauca-Betula nana (Childs 1969). Betula glandulosa-Salix planifolia-Vacciniumuliginosum (Steigers and others 1983). Betula glandulosa-Salix spp.-Eriophorumspp./Hylocornium splendens (McCartney 1976, Talbot and others 1984).ll.C.2.g. Open Low Willow ShrubDescription-These communities have 25 to 75 percent cover of shrubs (primarilywillows), at least 20 centimeters (8 in) tall (fig. 47). Shrubs taller than 1.5 meters(5 ft) provide less than 25 percent cover and trees overtopping the shrubs provideless than 10 percent cover. The understory is generally dominated by dwarfshrubs or forbs. Willows commonly dominant include Salix glauca, S. planifoliaand S. lanata. Trees are generally absent. Shrubs important in the understoryinclude ericaceous shrubs such as Arctostaphylos rubra and Vaccinium uliginosum,dwarf willows such as Salix reticulafa, or subshrubs such as Dryas spp. Commonunderstory species include Petasites frigidus, Fesfuca altaica, Carex bigelowii, andArtemisia arctica. Nonsphagnaceous mosses may form patchy to continuous mats.On wet sites, Sphagnumspp. are sometimes present. Lichens are generallyunimportant.137