The Alaska Vegetation Classification - Alaska Geobotany Center ...

Figure SB--Dry graminoid herbaceous stand of Elymusarenarius with Senecio pseudoarnica and Medensiamaririma on sand dunes in the Aleutian Islands.Elymus arenarius ranges in height from around 20 centimeters (8 in) in the Arcticto over 1 meter (311) in the southern part of the State. Elymus innovatus is usually30 to 70 centimeters (12 to 30 in) tall depending on site conditions. Vegetative coverof communities of both species may be complete or sparse.Distribution and site characteristics-Hymus arenarius communities are characteristicof coastal and near-coastal sand dunes and the upper parts of coastalsand beaches around the State. Exceptions are the Aleutian Island communitieswhere dominance is shared by ferns or large forbs of the family Umbelliferae(Apiaceae), which do not occur on coastal sands but on well-drained, mesic soils onslopes. In northen Alaska, because of the small tidal range and the extreme erosiveforce periodically exerted on beaches by storms, elymus communities are rare onexposed beaches and more commonly are found on the inland side of spits andbarrier islands. Along much of the Beaufort Sea coast, sand substrates are rare andelymus communities are restricted mostly to dune fields at river mouths and smallisolated pockets of sand scattered along the coast. Elymus innovatus communitiesform small localized stands on flood plains and dry south-facing slopes in the Alaskaand Brooks Ranges. Substrates of the coastal Elymus arenarius communities consistof circumneutral (pH 6.4 to 7.3) sands or pebbles. Although many of these communitiesare inundated by infrequent storm surges, water drains quickly without leavingany appreciable quantity of salt in the soil. Substrates of other elymus communitiesare well drained and consist of silt loams to river gravels. Permafrost is absent fromall but the most northern sites; even there it is at least 1 meter (3 ft) below thesurface.Successional status-Hymus arenarius is normally the first species to colonizeshifting dune sands. On beaches, elymus communities gradually replace halophyticherb communities as uplift or beach progradation decreases the frequency of tidalinundation. Increasing numbers of grasses, sedges, forbs, or low shrubs invade theelymus communities as the substrate is stabilized; the exact species depends on sitecharacteristics and location. In western Alaska, ericacious shrubs, particularly crowberry(Ernpetrum nigrurn), and several grasses and sedges gradually replace theelymus. In south-central and southeastern Alaska, succession proceeds throughvarious herbaceous and shrubby types to culminate in Sitka spruce forest.159