The Alaska Vegetation Classification - Alaska Geobotany Center ...

Distributlon and site characteristics-Overmature open birch stands are commonin interior and south-central Alaska. The open birch stands with a lichen understoryare apparently fairly rare; they occur mostly near the western tree line and near theelevational tree line of interior, western, and south-central Alaska. Elevational tree-linestands may have originated as a result of fires burning through white spruce stands.Moist sites, such as those near tree line, support shrubby understories. Dry sites,including stabilized sand dunes and possibly some elevational tree-line sites, supportfruticose lichens in the forest openings. Soils are moderately well drained in themature open upland birch sites. Permafrost is absent or with a deep active layer.Successional status-The successional status of many open birch stands is unknown.Some probably will be replaced by white spruce if sufficient time elapses.Others, particularly certain overmature birch communities in south-central Alaska,do not appear to be heading toward spruce dominance. Perhaps they are revertingto open shrub communities with grassy openings (Neiland and Viereck 1977).Closely related types-Open birch communities are similar to closed birch communitiesand birch woodland communities but have less tree cover than the formerand more tree cover than the latter (25 to 60 percent tree cover).Photographs-Racine 1976, figure 9; figure 29, this publicationPrimary references-Foote 1983, Hanson 1953, Neiland and Viereck 1977, Racine1976.Communities-BetulapapyriferdCladonia spp. (Racine 1976). Betula papyriferdBetula glandulosa/Hylocomium spp. (Hanson 1953; Hettinger and Janz 1974; Viereck1975, 1979). Betulapapyr-sifera/Viburnum edule/Calamagrostis spp. (Foote 1983).Betula papyriferdAlnus crispd~edumgroenlandicum (Jorgenson and others 1986).I.B.2,b. Open Quaking Aspen ForestDescription-Open quaking aspen stands aredominated by generally small aspen trees thatprovide roughly 10 to 60 percent canopy cover(fig. 30). These trees rarely are larger than12 centimeters (5 in) d.b.h. and 15 meters (50 ft)tall. A representative basal area is 8.7 squaremeters per hectare (37 ft'lacre). Rosa acicularis1 to 2 meters (3 to 6 ft) tall may be present.Shepherdia canadensis is a common lowshrub, and Arctostaphylos uva-urs-simay form apatchy ground cover. Common herbs includeCalamagrostis purpurascens, Galium boreale,and Pulsatilla patens. Neither mosses norlichens provide significant cover. Flood-plainsites may support substantial quantities of tallwillows in addition to the aspen.Figure 36Open broadleaf forest of quaking aspen with ashrub layer of Shepherdia canadensis and Rosa acicularisand an herbaceous layer of Calamagrostis purpurescens.Pulsardla patens, and the subshrub Arctosfaphylos uva-ursion a steep, south-facing bluff in interior Alaska.93