Lichen communities of black oak group (Quercus (Erythrobalanus) spp.) tree trunks in 29 study sites near the rural Columbia generating station, Portage, Wisconsin, were surveyed before (1974) and three years after (1978) station operations began, to determine if SO2 air pollution from the station had affected the communities. SO2 emissions from the station were relatively small: maximum 1 hr level was 389 micrograms SO2/cu m (15 pphm) and annual average concentrations were 5-9 micrograms SO2/cum (0.20-0.35 pphm). Some differences between lichen communities in higher- and lower-SO2 impact areas could be seen in 1978 survey. No lichen species were lost due to SO2, but communities in higher-SO2 areas exhibited more changes in species frequencies between 1974 and 1978 than did communities in lower-SO2 areas. Several common lichen species showed altered patterns of distribution and abundance in higher-SO2 impact areas. (Copyright (c) 1980 by the American Bryological and Lichenological Society, Inc.)