This system occurs above upper treeline throughout the Rocky Mountains and east into the mountain island ranges of central Montana. Elevation ranges from as low as 1,981 meters (6,500 feet) in northwestern Montana to 3,200 meters (10,500 feet) in southern Montana. The climate is very cold, with heavy snow accumulation and a very short growing season (60 to 90 days). This system occurs on level or concave glacial topography with late-lying snow and subirrigation from surrounding slopes. It can occur on all aspects, but is most common on north and east facing aspects. These sites are characterized as snow bed communities, where snow persists until mid or late summer, or occasionally, until fall. Soil temperatures remain colder than in the surrounding alpine meadows throughout the growing season. Soils are moist but well-drained, strongly acidic, and often with substantial peat layers. These dwarf shrublands are 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 (1.6 foot) in height. The ericaceous shrub community is dominated by western moss heather (Cassiope mertensiana), white arctic mountainheather (Cassiope tetragona), yellow mountain heath (Phyllodoce glanduliflora), pink mountain heath (Phyllodoce empetrifomis), and alpine bog laurel (Kalmia microphylla). Grouse whortleberry (Vaccinium scoparium), bilberry (Vaccinium myrtillus) or mountain huckleberry (Vaccinium membranaceum) are often found within the heath shrublands in northwestern Montana. The willow community forms localized thickets on level areas or on the perimeter of depressional areas and can be dominated by either mat forming or dwarf -shrub alpine willows (Salix spp.). The herbaceous understory is composed of a diversity of alpine sedges (Carex ssp.), rushes (Juncus spp.), woodrushes (Luzula spp.), alpine grasses and forbs.
This system is composed of dwarf shrublands of ericaceous dwarf-shrubs or dwarf, alpine willows forming a low shrubland ground cover less than 0.5 meters (1.6 feet) in height. The ericaceous shrub community is dominated by western moss heather, white arctic mountainheather, yellow mountain heath, pink mountain, and alpine bog laurel. Grouse whortleberry, bilberry, or mountain huckleberry are often found within the heath shrublands, especially in northwestern Montana. Common graminoids and forbs include showy sedge (Carex spectabilis), shortstalk sedge (Carex podocarpa), Rocky Mountain sedge (Carex scopulorum), Hitchcock’s woodrush (Luzula glabrata var. hitchcockii) and Piper’s woodrush (Luzula piperi). Forbs such as alpine pussytoes (Antennaria species), arnica (Arnica species), Indian paintbrush (Castilleja species), glacier lily (Erythronium grandiflorum), alpine Saint John’s wort (Hypericum formosum), viviparous bistort (Polygonum viviparum) and Rocky Mountain groundsel (Packera cymbalarioides) are found within the heath-dominated shrubland.
Willow dominated communities form localized thickets on more level areas or around the perimeter of depressional areas. These depressional areas can have greater peat development. Dwarf, mat-forming species such as arctic willow (Salix arctica) and snow willow (Salix reticulata) are common associates. Other willow bed communities composed of shrubs that are less than .5 metrs (1.6 feet) tall include undergreen willow (Salix commutata), grayleaf willow (Salix glauca), plane leaf willow (Salix planifolia), and, in areas underlain by calcareous parent material, shortfruit willow (Salix brachycarpa) (Bamberg and Major, 1968). Sedges and rushes dominate in the depressional or level areas and are usually the last to emerge after snowmelt. These areas are species poor and are dominated by black sedge (Carex nigricans), Drummond’s rush (Juncus drummondii) and tufted hairgrass (Deschampsia cespitosa) or purple mountain hairgrass (Vahlodea atropurpurea). Sibbaldia (Sibbaldia procumbens), Ross’ avens (Geum rossii), and marsh marigold (Caltha leptosepala) often occur in openings in the peat (Cooper et al., 1997). Alpine dwarf shrublands occur as distinct patch types within Rocky Mountain Alpine Fell-Fields or adjacent to Rocky Mountain Alpine-Montane Wet Meadows or at the upper elevational limit of Rocky Mountain Subalpine Woodlands and Parklands.
Cooper, Stephen V., Peter Lesica, and Deborah S. Page-Dumroese. 1997. Plant community classification for alpine vegetation on the Beaverhead National Forest, Montana. Ogden, UT (324 25th Street, Ogden 84401): U.S. Dept. of Agriculture, Forest Service, Intermountain Research Station.
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