The Alaska Vegetation Classification - Alaska Geobotany Center ...

Closely related types-Closed low alder-willow communities are similar to closedtall alder-willow communities and open low alder-willow communities, but the canopyis primarily less than 1.5 meters (5 11) tall and provides at least 75 percent cover.These communities also are similar to closed low willow communities but have asubstantial alder component.Primary reference-Wibbenmeyer and others 1982.Communltie+Alnus spp.-Salix spp. (Wibbenmeyer and others 1982).ll.C.2. Open Low ScrubOpen low scrub Communities are characterized by an open canopy (25 to 75 percentcover) of low shrubs (0.2 lo 1.5 meters [E in to 5 ft) tall). More specifically, they have25 to 75 percent cover by shrubs at least 20 centimeters (8 in) tall, shrubs taller than1.5 meters (5 it) provide less than 25 percent cover, and trees overtopping the shrubcanopy provide less than 10 percent cover. If low shrubs are the only plants present,cover can be as low as 2 percent. Many shrubby wetlands and tundra types are in-cluded in this unit. Many ericaceous shrubs sometimes grow shorter than 20 centimeters(8 in) and sometimes grow taller. In practice, ericaceous shrub communitieson wetlands and those containing shrub birch are treated as open low scrub. Otherericaceous shrub communities (primarily alpine heath vegetation) are treated in thedwarl scrub unit (1I.D.).II.C.2.a. Open Low Mlxed Shrub-Sedge Tussock TundraDescrlptlon-These communities have at least 25 percent shrub cover and are dominatedby tussock-forming sedges, usually Eriophorum vaginatum but sometimesCarex bigelowii. Tussocks are commonly 5 to 30 centimeters (2 to 12 in) high and15 to 35 centimeters 6 to 14 in) wide, often with a density of 2-4 tussocks1persquare meter (10.8Ift ) (Hopkins and Sigafoos 1951, Racine and Anderson 1979).Trees are absent or very scarce. Mosses and dwarf shlubs form a mat surroundingthe tussocks. Commn shrubs include Betulaglandulosa, 8. nana, Ledumdecumbens, Vaccinium vitis-idaea, and V. uliginosum. Other shrubs sometimescommn include Empetrum nigrum (especially in western Alaska), Rhododendronlapponicum (especially in calcareous areas), Salix planifolia, S. reticulafa, andArctostaphylos rubra. Rarely an open overstory of scatfered alders (Ahus crispa) orwillows up to 1 meter (3 ft) tall is present. Herbs other than the tussock-formers aregenerally scarce, though Rubus chamaemorus is locally commn and Arctagrostislatifolia. Poa arctica, Eriophorum angusfifolium (especially in frost scars), Pedicularislabradorica, and Perasires frigidus may be present. Common mosses includePleurozium schreberi, Hylocomium splendens, Aulacomnium spp., and Sphagnumspp. Sphagnum is often a rather minor constituent, or even absent, but is sometimesquite important. Lichens, such as Cetraria cucullata, C. islandica, Cladonia spp.,Cladina rangiferina. and Jhamnolia subuliformis, may be common.128