This widespread ecological system occurs above upper timberline throughout the Rocky Mountain cordillera, including alpine areas of ranges in Utah and Nevada, and north into Canada. Elevations are above 3360 m in the Colorado Rockies but drop to less than 2100 m in northwestern Montana and in the mountains of Alberta. This system occurs in areas of level or concave glacial topography, with late-lying snow and subirrigation from surrounding slopes. Soils have become relatively stabilized in these sites, are moist but well-drained, strongly acidic, and often with substantial peat layers. Vegetation in these areas is controlled by snow retention, wind desiccation, permafrost, and a short growing season. This ecological system is characterized by a semi-continuous layer of ericaceous dwarf-shrubs or dwarf willows which form a heath type ground cover less than 0.5 m in height. Dense tuffs of graminoids and scattered forbs occur. Dryas octopetala or Dryas integrifolia communities are not included here, except for one very moist association, because they occur on more windswept and drier sites than the heath communities. Within these communities. Cassiope mertensiana, Salix arctica, Salix reticulata, Salix vestita, or Phyllodoce empetriformis can be dominant shrubs. Vaccinium spp., Ledum glandulosum, Phyllodoce glanduliflora, and Kalmia microphylla may also be shrub associates. The herbaceous layer is a mixture of forbs and graminoids, especially sedges, including, Erigeron spp., Luetkea pectinata, Antennaria lanata, Oreostemma alpigenum (= Aster alpigenus), Pedicularis spp., Castilleja spp., Deschampsia caespitosa, Caltha leptosepala, Erythronium spp., Juncus parryi, Luzula piperi, Carex spectabilis, Carex nigricans, and Polygonum bistortoides. Fellfields often intermingle with the alpine dwarf-shrubland.
Information Source: http://www.natureserve.org/explorer/