The relationships between traffic-related air pollution, bark pH and epiphytic lichen mycota on Pinus sylvestris and Tilia cordata were studied. Traffic is considered the main source of air pollution in Tallinn and, therefore, greatly influences lichen composition and species richness, their diversity increasing on Pinus sylvestris near roadways but decreasing on Tilia cordata. Traffic also affected bark pH of Pinus sylvestris, but not of Tilia cordata: the bark of Pinus sylvestris is normally acid (mean pH in control plot 3.0) and is modified to subneutral (up to 5.7) near roadways. The influence of alkaline dust pollution, connected with traffic, is clearly observed on epiphytic lichen composition of P. sylvestris in Tallinn. Besides dust, nitrogen oxides are important pollutants too, but the effects of acidic air pollution are less evident now compared to the previous studies.
