The Alaska Vegetation Classification - Alaska Geobotany Center ...

Figure 41-Open tall willow shrub of Salix bebbiana witha low shrub layer of Vaccnium uliginosum and Ledumgroenlandicum and a herbaceous layer of Equiseiumawense and Epilobium angustifolium that has developedafter a fire in black spruce in interior Alaska.layers may contain Calamagrostis canadensis, Epilobium angustifolium, Geraniumerianthum, Aconitum delphinifolium, and other forbs. Mosses may be common orabsent. Rhacomitrium canescens may be present on dry gravelly sites; Polyfrichumspp., Hylocomium splendens, and Drepanocladus uncinatus may be common onmesic sites. Lichens are generally rare, which reflects the early successional statusof most of these stands.Distribution and site characteristlcs-Open tall willow communities occur on floodplains and recent outwash deposits. They also occur on sand dunes, in drainageways,and on sheltered slopes. They are common throughout most of the Stateexcept for southeastern Alaska and the Aleutian Islands. The substrate consists ofexcessively drained alluvial sands and gravels or loams. The coarser substrates tendto be quite dry except when flooded. Flood-plain sites are subject to periodic flooding.Most flood-plain sites lack relief, but in some fine-textured soils, hummocks andhollows may be present. In forested areas permafrost is absent or far below thesurface; in tundra areas the active layer may be as shallow as 30 centimeters (12 in).Successional status-Flood-plain open tall willow communities frequently developfrom seral herb communities as willow seedlings grow and begin to dominate. Inforested parts of the State, most of these communities will be replaced by trees afterseveral intermediate stages if the communities are not redisturbed by flooding orerosion. In tundra areas, the willows eventually become decadent and do not growas tall as an organic soil layer builds up and soil temperatures decrease. The willowsusually are replaced by dwarf shrub-sedge tussock tundra or, in some cases, wetsedge meadow tundra. Successional relations of nonflood-plain open tall willowstands are mostly unknown.Closely related typesopen tall willow communities are similar to closed tall willowcommunities but have less than 75 percent cover. They also are similar to open lowwillow communities but are taller with canopy heights averaging 1.5 meters (5 ft) ormore. Some stands may be similar to open tall alder-willow or open tall birch-willow,but alders and birches are absent or only minor components of willow communities.Photographs-Figure 41, this publication.Primary references-Hanson 1951, Ritchie and others 1981, Viereck 1970a,Webber and others 1978.119