This shrubland ecological system is found within the zone of continuous forest in the upper montane and lower subalpine zones along both sides of the Continental Divide from southwestern to northwestern Montana, and in the island mountain ranges. Soils tend to be moist to wet. It is found on steep mountain slopes, usually on north and east facing aspects. In northwestern and west-central Montana, it forms within upper montane Douglas-fir (Pseudotsuga menziesii) and Engelmann spruce-subalpine fir (Picea engelmanii/ Abies lasiocarpa) forests on steep slopes and ravines. Soils are usually shallow, rocky or gravelly with good aeration and drainage. Occurrences are typically found in locations with cold-air drainage or ponding, or where snowpacks linger late into the summer, such as north-facing slopes and high-elevation ravines. They can extend down in elevation to the montane zone in places where cold-air ponding occurs, especially on north and east aspects. In northwestern Montana, elevation ranges from 1,525 to 1,950 meters (5,000 to 6,400 feet) west and immediately east of the Continental Divide and up to 2,682 meters (8,800 feet) in southwestern Montana. Common shrub species include rusty leaf menziesia (Menziesia ferruginea), black twinberry (Lonicera involucrata), alder buckthorn (Rhamnus alnifolia), prickly currant (Ribes lacustre), thimbleberry (Rubus parviflorus), sitka alder (Alnus viridis), cascade mountain ash (Sorbus scopulina), Sitka mountain ash (Sorbus sitchensis), and thinleaf huckleberry (Vaccinium membranaceum).
These shrubland communities develop on steep mountain slopes, at the heads of cirque basin drainages, and on upper elevation toeslopes within the mesic montane and subalpine forest zones. Common shrub species include rusty-leaf menziesia, black twinberry, alder buckthorn, prickly currant, thimbleberry, Sitka alder, cascade mountain ash, sitka mountain ash, and thinleaf huckleberry. Extensive stands of mountain huckleberry are important summer and fall foraging areas for grizzly and black bears.
On some sites in northwestern Montana, rusty leaf menziesiaand Sitka alder can form nearly impenetrable stands. Drier aspects of this community can also support stands of thimbleberry, Canadian buffaloberrry (Shepherdia canadensis), birchleaf spiraea (Spiraea betulifolia), and deerbrush ceanothus (Ceanothus velutinus).
The herbaceous understory can be sparse on sites with dense shrub cover. Common graminoids include bluejoint reedgrass (Calamagrostis canadensis), pinegrass (Calamagrostis rubescens), sedges (Carex species), and blue wildrye (Elymus glaucus). Common forbs and ferns include beargrass (Xerophyllum tenax), fireweed (Chamerion angustifolium), and bracken fern (Pteridium aquilinum), reflecting the mesic nature of many of these shrublands. Other forb species include baneberry (Actaea rubra), arnica (Arnica species), queen’s cup beadlily (Clintonia uniflora), boreal bedstraw (Galium triflorum), twinflower (Linnaea borealis), clasp-leaf twisted stalk(Streptopus amplexifolius), and western meadow rue (Thalictrum occidentale). Post-fire communities are often dominated by fireweed, yarrow (Achillea millefolium), nettle-leaf giant hyssop (Agastache urticifolia), aster (Symphyotrichum spp.), goldenrod (Solidago spp.), and pearly everlasting (Anaphalis margaritacea).
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