This diploma thesis was focused on the community ecology of corticolous subaerial cyanobacteria and algae. Altogether 54 morphotypes were identified on the surface of the tree bark in the Nature Reserve Březina in České středohoří Mts., Czech Republic. Compared to publish data on tropical and subtropical habitats, high morphological diversity of these organisms in a temperate region was thus recognized. Coccoid green algae - most of them belonging to the class Trebouxio-phyceae - dominated. In a study focused on the algae community structure at small spatial scales (such as a single tree trunk), the temporal factors were found as the most important factor influencing the species composition. The height of a sample on trunks and type of bark roughness seemed to influence the species richness, yet the differences were not significant. The alpha-diversity and species composition of corticolous algal communities among individual trees were strongly influenced by host tree species. The pH of the bark surface also had significant impact on species composition. Generally, trees with lower pH of the bark surface (alder, spruce) had lower species richness, whereas trees with more alkaline bark surface (ash, beech, maple) had higher alpha-diversity values. Considering the generally efficient dispersal ability of...