Epiphyte diversity and abundance were examined along the Fraser River and its tributaries in central-interior British Columbia at varying distances from point-source air pollution discharges. Black cottonwood (Populus balsamifera L. ssp. trichocarpa (Torr. & A. Gray ex Hook.) Brayshaw trunks near discharges in Prince George had comparatively low epiphyte diversity and supported an unusual acidiphilic lichen community, including Tuckermannopsis chlorophylla (Willd.) Hale, Usnea lapponica Vain., and Vulpicida canadensis (Räsänen) J.-E. Mattsson & M.J. Lai. At a greater distance from air pollution sources, a more characteristic flora was observed, including Collema Wigg. spp., Lecidea erythrophaea Flörke, Leptogium (Ach.) Gray spp., Lobaria pulmonaria (L.)Hoffm., Nephroma parile (Ach.) Ach., Peltigera Willd. spp., and Strangospora moriformis (Ach.) Stein. These changes were accompanied by large differences in bark pH; mean values ranged from 3.7 in Prince George to 6.7 in upriver stands for black cottonwoods, from 3.5 to 5.4 for live spruce branches (Picea glauca (Moench) Voss), and from 3.1 to 4.9 for dead spruce branches, respectively. Epiphyte communities proximal to Prince George were characterized by many nitrophilous species. Our data showed a strong covariate influence of climate, with Lobarion community lichens more abundant in the easternmost highprecipitation plots. Numerous provincial-and global-level conservation priority species were found, including Collema quadrifidum D.F. Stone & McCune, newly discovered for Canada; Collema coniophilum Goward, a Species at Risk Act listed species; and provincially at risk Heterodermia speciosa (Wulf.) Trev., Physcia tribacia (Ach.) Nyl., and Santessoniella saximontana T. Sprib., P.M. Jørg. & M. Schultz, mostly in sites distant from air pollution sources.