Comm #8087
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Salix arctica / Polygonum bistortoides Dwarf-shrubland
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accession code: VB.CC.27256.SALIXARCTICAPOL
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Western Ecology Working Group of... |
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This alpine association has been defined for southwestern Montana in the East Pioneer and Anaconda-Pintlar ranges, as well as in Glacier National Park in northwestern Montana. This community occurs primarily as small patches, from the uppermost subalpine to the highest alpine elevations, from 1980 to 2440 m (6495-7990 feet). It is mainly associated with receiving positions, toeslopes and lower to midslopes of gentle terrain. Slopes range from flat to moderate with all aspects represented, though steeper slopes tend to have northerly or easterly exposures. This community is also noted to occur downslope from snowbed communities, which may augment its moisture supply. Substrates include various sedimentary rock types, both calcareous (limestone) and not (siltstones, argillite). The type occurs predominantly in small, visually salient patches that appear as a continuous blanket of green due to high coverage of both the vascular (shrubs 50%, graminoids 15%, and forbs 30%) and bryophyte (50%) components. Salix arctica is both dominant and diagnostic; Dryas octopetala is the only other shrub of note, though its cover seldom exceeds 10%. Poa alpina and moist-site Carex spp. (Carex albonigra, Carex phaeocephala, and Carex nova) contribute the most to graminoid cover. Cover of the diagnostic forb Polygonum bistortoides generally exceeds 10%, but other forbs, including Polygonum viviparum, Geum rossii, Potentilla diversifolia, Oreostemma alpigenum (= Aster alpigenus) and Claytonia lanceolata, are often codominant. This association most often grades to moist turf types or unequivocal snowbed communities (e.g., Carex nigricans Herbaceous Vegetation (CEGL001816)) or wet meadows (e.g., Deschampsia caespitosa - Caltha leptosepala Herbaceous Vegetation (CEGL001882)). Most other dwarf-shrub Salix spp.-dominated types occur on yet wetter sites, therefore they should be recognized first in working keys. The dominance of Salix arctica is diagnostic for the alliance of the same name but how this plant association is distinguished from others within the alliance has not been addressed. |
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