Distributions of seven species or groups of species of epiphytic lichens were registered at 193 sites of Scots pine (Pinus sylvestris L.) forest regularly distributed throughout Norway. These were Hypogymnia physodes (L.) Nyl., Pseudevernia furfuracea (L.) Zopf, Parmeliopsis spp., Bryoria spp., Usnea spp., "other foliose species" and "crustose species". Abundances were measured by a measuring-tape technique on the trunks of four pine trees at each site, with the purpose of relating the largescale distribution of the lichens to environmental parameters and gaining a better understanding of the factors regulating lichen occurrence. Multivariate numerical analyses (DCA and PCA) and multiple regression analyses were applied to the lichen and environmental data. The mean lichen cover at the sites varied from 0.2% to 56.7%, being highest along the coast of southern Norway and considerably less inland, in mountainous areas and in the north. By far the most abundant species was Hypogymnia physodes. Bryoria and Parmeliopsis species had a continental and somewhat northern distribution. Usnea species were rather unevenly distributed, but were sparse both in the highest pollution deposition areas in the south Hypogymnia physodes and Pseudevernia furfuracea were most abundant in the southern, warmer parts of the country. The collective groups "other foliose species" and "crustose species" were most abundant along the west and south coasts. The main factors determining lichen occurrence and abundance on trunks of Scots pine would seem to be those associated with temperature and moisture. Forest density also seems important. Since air pollution deposition in Norway is highly dependent on precipitation and varies along a south-north and coast-inland gradient, it is difficult to separate the effects of pollution from the effects of climatic variation. The scarcity of Bryoria and Usnea species in the southern parts of the country, however, might be attributable to air pollution.
