SPOTTED KNAPWEED DISTRIBUTION IN STOCK CAMPS AND TRAILS OF THE SELWAY-BITTERROOT WILDERNESS

This article documents spotted knapweed (Centaurea maculosa Lam.) in 3 0 campsites and along 5 trails in the Selway-Bitterroot Wilderness and assesses the role of disturbance and environmental factors in control ling infestation. Spotted knapweed was present in only 6 of 30 surveye d campsites and limited portions of all 5 trails that were sampled. Al l spotted knapweed in camps was below 1700 m elevation, in open canopy , and in areas with an opportunity class disturbance ranking of 3 or 4 . Overall disturbance levels measured using U.S. Forest Service Site I mpact Worksheets (SIWs) did not help predict occurrence of spotted kna pweed, although bare mineral soil, vegetation loss, and development va riables of SIWs provide some explanation of spotted knapweed presence or absence. There was no significant difference in knapweed frequency between areas used predominantly by horses and those used by humans wi thin camps. Over 95% of spotted knapweed along trails was found within 0.5 km of the trailhead, occurred within 4.6 m of the trail, and had low reproductive potential. If the Bitterroot portion of the Selway-Bi tterroot Wilderness is representative of forested wilderness areas in the Northern Rockies, then the perceived threat of spotted knapweed to wilderness areas may substantially exceed the actual danger in many i nstances. Study findings indicate that managers should conduct surveys before initiating costly control measures in wilderness areas, that e radication may be a viable alternative when spotted knapweed numbers a re this low, and that regulations promoting minimum-impact camping sho uld reduce spotted knapweed infestation.