The Alaska Vegetation Classification - Alaska Geobotany Center ...

The sites themselves are covered with snow through part or most of the summer.Species present must adapt to a short growing season.Successional status-These specialized communities are not likely to change aslong as winter precipitation and wind patterns do not change significantly.Closely related types-These communities may resemble mesic sedge-herbmeadow tundra but have a more open vegetative cover and less sedge cover andare located in snowbeds. In some cases, these snowbed communities may gradeinto alpine herb communities on adjacent talus, but a topographic break and changesin species usually separate the two. Open dwarf scrub snowbed communities aredominated by prostrate mat-forming shrubs, are usually more densely vegetated thanalpine herb-sedge snowbeds, and occur on sites with long growing seasons.Prlmary references4ohnson and others 1966, Scott 1974a.Communities-Cetraria delisei-Oxyria digyna-Koenigia islandica-Saxifraga rivularis(Johnson and others 1966). Carex lachenalii-Oxyria digyna-Claytonia sarmenfosa(Scott 1974a). Rhacomifrium canescens-Dicranoweisia cirrafa-Oxyria digyna (Scott1974a). Anthelia julacea-Scapania paludosa-Saxifraga hirculus-Lepfarrhena pyrolifolia(Shacklette and others 1969). Rubus arcticus-Sedum mea-Polygonumbisforta-Saxifraga hirculus (Racine and Young 1978). Carex nigricans (Jaques 1973).III.5.l.c. Alpine HerbsDescription-Alpine herb communities consist of sparse vegetation on talus andblockfields. A wide variety of herbs may be present, often with no particular speciesdominating. Species commonly present include Draba spp., Saxifraga spp., Festucabrachyphylla, Potentilla spp., Diapensia lapponica, Oxyria digyna, Androsace spp.,Epilobium latifolium, and Smelowskia spp. Woody plants are absent or nearly so.Small patches of mosses such as Andreaea spp. may be present between rocks.Lichens, especially crustose lichens, may be common. These communities are openwith much bare rock between individual plants.Distribution and site characteristics-Alpine herb communities occur on talus, rockoutcrops, and blockfields throughout the State. These are sites too steep or toowindblown for soil development. The substrate consists of lithosols or regosolsbetween rocks.Successional status-These are early successional communities colonizing stony,unvegetated surfaces. They persist at these sites indefinitely because soil formationis slow and fine materials are either blown away or moved downslope as soon asthey are formed.Closely related types-Alpine herb communities are very similar to seral herbcommunities, but seral communities occur primarily on flood plains, cutbanks, andother sites where succession to other communities will occur fairly rapidly afterdisturbance ceases. Alpine herb communities are maintained in a successional stateindefinitely by steep slopes and wind erosion. Some species are common in bothcommunities (notably Epilobium lafifolium). Others, such as Artemisia tilesiiandEedysarum mackenzii, are more typical of seral herb communities. Still others, suchas Draba spp. and Smelowskia spp., are more typical of alpine herb communities.191