BC to cent. Calif., N. Idaho
"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.
In some areas, Cascade barberry is browsed by black-tailed deer. In other locations it is seldom used. Harcombe reported moderate use of Cascade barberry by Roosevelt elk during winter but not in the spring or summer. Various small mammals feed extensively on the foliage. It is, for example, an extremely important dietary component of the white-footed vole in the Coast Ranges of Oregon . Cascade barberry comprised 32 percent of the vole's diet in February but declined to 17 percent by June. The value of dwarf Oregon-grape browse to domestic livestock is apparently low in most locations. Utilization by domestic sheep in the Cascade Ranges in Washington may reach 6.8 to 23.7 percent. The fruits are readily eaten by many small birds and mammals. In some areas, black-tailed deer also eat the fruits. The nectar of several species within the genus Berberis is favored by the Anna's hummingbird...
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 ." 
For rehabilitation of disturbed sites, "Cascade barberry can be easily propagated from seed and from rhizome or stem cuttings. However, plants may be slow to establish . Detailed information on propagation techniques is available." 
 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.