Lichens are an important group of organisms in terms of environmental issues, conservation biology and biodiversity, principally due to their sensitivity to changes in their environment. Therefore it is important that we develop our understanding of the factors that affect lichen distribution. In this thesis, both spatial and temporal distributions of epiphytic lichens at different scales have been studied in southern Sweden.

Generation time of the red-listed lichen Cliostomum corrugatum was examined using Bjärka-Säby as the study site. The results showed that the average age of an individual of C. corrugatum is 25–30 years at the onset of spore production.

The rarity of C. corrugatum was also examined. DNA analysis of an intron from 85 samples, collected at five sites in Östergötland, yielded 11 haplotypes. Results from coalescent analysis, mantel test and AMOVA indicated that C. corrugatum have a high ability to disperse. The study concluded that its rarity is most likely connected with the low amount of available habitat, old Quercus robur.

The changes in the distribution of epiphytic lichens in southern Sweden, between 1986 and 2003, were also compared. For each year a centroid was calculated on all combinations of tree and lichen species. The three significant cases showed that the centroid movement pointed toward a north-east or north-north-east direction.

Finally differences in species richness and cover of lichens on large Q. robur were examined between urban and rural environment. The results demonstrated that species number and percent cover was significantly higher on oaks standing rural compared to oaks standing urban. Effects of urban sprawl showed a decline in species richness and cover with increasing age of the surrounding buildings.