Lichens are an important group of organisms in terms of environmental issues, conservation biology and biodiversity, since lichens are sensitive 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.

Brokind was chosen as the study site to investigate the succession of epiphytic lichens on Quercus robur using a chronosequencial approach. Fourteen of the investigated taxa out of 50 proved to be significant. The taxa were divided into three groups according to whether they occurred on young, middle-aged or old trees.

Generation length 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.

Generation length 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 of an intron from 85 samples, collected at five sites in Östergötland, yielded 11 haplotypes. Results from the 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 Q. robur.

The changes in the distribution of epiphytic lichens in southern Sweden between 1986 and 2003 were 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.

Regional gradients of abundance and size of Hypogymnia physodes at 66 sites in southern Sweden were examined. The coordinate system rotating the reference system of investigated sites around the origin was used to search for the best explanatory power for the angle of the explanatory variables. The results showed a gradient of increase in the probability of occurrence in a north-north-east direction and an increase in diameter on thallus size in a west-north-west direction.