W. North America
"In many parts of the Pacific Northwest, Douglas-fir-western hemlock/Cascade barberry and western hemlock/Cascade barberry-salal habitat types provide important big game wintering areas. Stands often offer good structural diversity and remain relatively snow-free. However, where dense shrub thickets develop, big game use may be limited. Western hemlock/Cascade barberry-Oregon oxalis and western hemlock/Cascade barberry-deerfoot vanillaleaf types serve as big game summer range.
Cascade barberry presumably provides cover for small birds and mammals. The diverse structure of western hemlock/dwarf Oregon-grape-salal types provides good big game hiding cover. Pacific silver fir/Cascade barberry and western hemlock/dwarf Oregon-grape-Oregon oxalis communities offer good thermal cover for deer and elk." 
"Cascade barberry fruits are tart but edible. Native peoples of the Pacific Northwest traditionally ate the fruits and made medicinal teas from the boiled roots. Dyes for baskets were also obtained from the roots.
Cascade barberry is a popular ornamental. It is well suited for shady locations and is widely planted in gardens throughout the Pacific Northwest. Its attractive foliage and short stature make it a particularly effective border plant. Although it multiplies well under cultivation, it does not form dense thickets. Foliage often turns a striking reddish-purple in winter after exposure to cold temperatures ." 
Little value as graze for livestock, and slow to establish for rehabilitation. 
 Tirmenstein, D. A. 1990. Mahonia nervosa. In: Fire Effects Information System,. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/shrub/mahner/all.html.