This shrubland system is found in the lower montane and foothill regions in the Rocky Mountains, including east into the island mountain ranges. It also occurs in southern Montana, where it forms compositionally diverse shrublands. It is common in foothills and lower slopes of mountain ranges, along higher creeks, and in draws and ravines of high plateaus on the northwestern Great Plains. The communities in this system grow at the interface between larger riparian areas and the adjacent upland shrublands and forests, usually occurring as small dense thickets, narrow bands, or irregular patches. The elevational range is 680 to 2,652 meters (2,234-8,700 feet). Shrub cover ranges from 30 to 100 percent. In Montana, chokecherry (Prunus virginiana) is frequently the dominant shrub species and on some sites, American plum (Prunus americana) may be solely present or co-dominant. Other shrubs associated with Prunus-dominated shrublands include currant (Ribes species), skunkbush sumac (Rhus trilobata), western snowberry (Symphoricarpos occidentalis), serviceberry (Amelanchier alnifolia), elderberry (Sambucus spp.), birchleaf spiraea (Spiraea betulifolia), andboreal sagewort (Artemisia frigida). Antelope bitterbrush (Purshia tridentata), creeping Oregon grape (Mahonia repens), and Woods rose (Rosa woodsii) may be present in some stands, along with scattered Rocky Mountain juniper (Juniperus scopulorum).
Stands can be dominated by one species but are often a mix of three to six shrub species, which can be as abundant or even more abundant than the dominant species. In Montana, for example, chokecherry is frequently the dominant shrub species and on some sites, American plum may be solely present or co-dominant. Other shrubs associated with Prunus-dominated shrublands include currant, skunkbush sumac, western snowberry, serviceberry, elderberry, birchleaf spiraea andboreal sagewort. Antelope bitterbrush, creeping Oregon grape, and Woods’ rose may be present in some stands, along with scattered Rocky Mountain juniper.
In drainage bottoms, herbaceous cover is usually less than 10 percent. On slopes, shrubs typically occur within grasslands, and graminoid cover can be greater than 75 percent. Graminoid species include mountain brome (Bromus carinatus), needle and thread (Hesperostipa comata), basin wildrye (Leymus cinereus), and bluebunch wheatgrass (Pseudoroegneria spicata). Mesic sites support forb species such ascow parsnip (Heracleum maximum) and starry Solomon’s seal (Maianthemum stellatum). Smooth brome (Bromusinermis), cheatgrass (Bromus tectorum), Kentucky bluegrass (Poa pratensis), and Canadian thistle (Cirsium arvense) are introduced species.
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