The Alaska Vegetation Classification - Alaska Geobotany Center ...

Distribution and site characteristics-Open low alder-willow shrub occurs on steepnorth slopes and along drainageways near tree line in interior Alaska and on riverterraces in northern Alaska. The shrubs and mosses form a hummocky mat overmineral soil or rocks. Permafrost is probably present at most of these sites, but thethickness of the active layer has not been measured.Successional status-These communities are probably fairly stable at many sites.With decreasing elevation and decreasing slope steepness, communities on drainagewaysgrade into tall alder-willow communities. North Slope terrace communitiesprobably become shrub-tussock tundra communities as the permafrost table risesand soils become colder and wetter.Closely related types-Open low alder-willow shrub communities are similar toopen tall alder-willow shrub and closed low alder-willow shrub but are composedprimarily of low (less than 1.5 meters [5 ft] tall) shrubs and have open (less than75 percent) shrub canopies. They also are similar to open low alder and open lowwillow communities but have substantial cover of both kinds of shrubs. Some standsmay be similar to shrub-tussock tundra but have more and usually taller alders andwillows and few tussocks.Primary references-Bliss and Cantlon 1957, Brock and Burke 1980, Viereck 1963.Communities-Alnus crispa-Salix spp./Carex bigelowii-Empefrum nigrum-Vacciniumvifis-idaea/Cefraria cucullafa-Cladonia spp. (Bliss and Cantlon 1957, Viereck 1963).Alnus crispa-Salix planifoliaEriophorum angusfifolium/Sphagnum spp. (Brock andBurke 1980).ll.C.2.1. Open Low Alder ShrubDescription-These communities have 25 to 75 percent cover of shrubs at least 20centimeters (8 in) tall, which are primarily alders. Shrubs taller than 1.5 meters (5 ft)provide less than 25 percent cover and tree canopy cover is less than 10 percent.Ahus crispa dominates most of these communities, but A. fenuifolia is dominant insome stands. Common understory species include Betula nana and the ericaceousshrubs Ledum decumbens, Empetrum nigrum, Vacciniurn uliginosum, V. vifis-idaea,and Arctostaphylos alpina. Carex bigelowii is often present, and friophorurnvaginatum tussocks may be present but not abundant. Mosses, such as Hylocomiumsplendens, Aulacomnium spp., Tomenfhypnum nifens, and sometimes Sphagnumspp., form a continuous mat.Distribution and site characteristics-Open low alder shrub occurs on gentlealpine slopes, broad drainageways, and locally in poorly drained flats in southwestern,south-central, and interior Alaska and on river terraces in northern Alaska.The substrate consists of an organic mat over mineral soil and is generally acid.Permafrost is present at many of these sites.Successional status-Successional relations are unknown. In northern Alaska,open low alder communities seem to occur in areas adjacent to and slightly betterdrained than areas supporting shrub-tussock tundra. Sometimes these areas arequite moist, but the water is moving (for example, open low alder shrub in broaddrainageways receiving water from shrub-tussock tundra upslope). On level groundaway from drainageways, open low alder shrub may give way to shrub-tussocktundra as the permafrost table rises and the soil becomes wetter and colder.143