The thesis deals with the study of changes in species composition and diversity in the plant communities of Fageto-Quercetum group of forest type with dominancy of Quercus petraea. We analysed these recent changes through data based on resurveying typological representative plots of forest typology located in the second level of the forest vegetation on andesite bedrock of Slovenské stredohorie Mts. These plots were in this region established during detailed typological survey between 1961 and 1974. The methodology of the resurveying 146 typological representative plots was identical to the methodology when they were set up. The data obtained from restored as well as the data from original plots were analysed in the JUICE and CANOCO programs. After evaluating of the results, we can state that changes in the oak forests communities of Slovenské stredohorie Mts. are relatively similar with changes in plant communities on whole temperate Europe. And that specifically to significant decline of fidelity, frequency and average cover of thermophilic species, acidophilus resp. mesotrophic mesophytes. On the contrary, species with increase fidelity, frequency and average cover are eutrophic even nitrophilous with wide amplitude to temperature and moisture. Decline of this species groups can be explained by anthropogenic eutrophication and also with increasing concurrency of tree species like Carpinus betulus, Fagus sylvatica and Acer campestre in the lower canopy layers. Other possible causes of these changes and their consequences are discussed in the discussion.