Estimating the susceptibility of wildland vegetation to trailside alteration.
The frequency and cover of understorey species was determined adjacent to and 10 m distant from trails through 6 forested and 2 meadow ecosystems in the Eagle Cap Wilderness, Oregon. The impact of the trail on the ecosystem was determined by measurement of the coefficient of floristic dissimilarity (FD), a function of the difference in cover and frequency of each plant species at varying distances from the trail. The effect of the trail on the ecosystem, as indicated by the FD coefficient, was greatest in Pseudotsuga menziesii/Physocarpus malvaceus, Picea engelmannii/Thalictrum occidentale and Abies lasiocarpa/Vaccinium scoparium vegetation types, in which the understorey plants were mesophytic forbs or woody shrubs with brittle stems and branches. The vegetation types least susceptible to damage were Pseudotsuga menziesii/Calamagrostis rubescens savanna, and grassland and meadow ecosystems.