The Alaska Vegetation Classification - Alaska Geobotany Center ...

11.0.1. Dtyas Dwarf ScrubThese are dwarf scrub communities dominated by species of the genus Dryas.Ericaceous shrubs, willows, sedges, and lichens may be abundant or evencodominant.1I.D.l.a. Dryas Dwarf Shrub TundraDescrlptlon-These communities are dominated by species of the genus Dryas,which form mats a few centimeters thick (figs. 52 and 53). Dwarf shlubs other thandryas may be absent or common, or sometimes even codominant. Common dwarfshrubs include ericads Vacciniurn vitis-idaea. V. uliginosurn, Cassiope tetragona,Arctostaphylos alpha, and A. rubra, and prostrate willows Salix reticulata andS. phlebophylla. Shrub birch is absent or nearly so, as are shrubby willows such asSalix glauca and S. brachycarpa. Graminoids, such as Hierochlo.5 alpina. Triseturnspicaturn, Carex rnicrochaeta, and C. scirpoidea may be present, but provide littlecover. Forbs, including Oxyfropis nigrescens, Hedysarurn alpinurn, Minuarfiaspp., Anemone spp., and Saxifraga spp. may be common. Mosses, such asTornenthypnurn nitens and Rhacornitriurn spp., usually are present in smallquantities, and lichens (such as Cetraria cucullata, Cetraria spp.. Cladina alpestris,Tharnnolia spp., and Stereocaulon spp.) may be common but not codominant. Treesare absent, and shrubs taller than 20 centimeters (8 in) are absent or provide lessthan 25 percent cover. Plant cover ranges from sparse to complete. Patterns,commonly steps or stripes, may be present.Dlstrlbutlon and site characteristics-Dryas dwarf shrub tundra is common onwindswept alpine sites throughout the northern two-thirds of the State and occasionallyis present on well-drained, exposed arctic lowland sites. Soils are mostlythin, well drained, and stony (generally Pergelic Cryaquolls, Cryoborolls, orCryochrepts). Permafrost usually is present, but the active layer is at least 50 centimeters(20 in) thick and usually much thicker. Most sites are exposed to strongwinds, which remove fines and organic material.Successional status-Successional relations are largely unknown. Most of thesecommunities are probably quite stable. Soils change very slowly in these exposedsettings, which creates a relatively constant environment for plant growth.Closely related types-Dryas tundra is similar to dryas-sedge tundra and dryaslichentundra but has fewer sedges and lichens, respectively. Some stands may besimilar to dwarf ericaceous tundra or dwarf willow tundra, but ericaceous shrubs andwillows, if present at all, are subordinate to dryas in the dryas tundra communities.Some open low shrub communities (such as low willow and mesic shrub birchericaceousshrub) have large quantities of dryas, but dryas tundra lacks shrub birchand erect shrubby willows.Photographs-Johnson and others 1966, figures 2 and 6; Racine and Anderson1979, figure 12; figures 52 and 53, this publication.Primary references-Johnson and others 1966; Jorgenson 1984; Komarkova andWebber 1978; Racine and Anderson 1979; Viereck 1962, 1963; Webber and others1978.