Phytosociological relevés from a natural acidophilous oak forest Calamagrostio−Quercetum, as well as Scots pine, Douglas fir and beech plantations located in the same habitat were analysed. Our investigations did not confirm the negative effect of Scots pine on biodiversity. We observed a decline of species number with the decrease of light availability. The undergrowth biodiversity in the oak forest was reduced by the presence of beech the most. The observed quantitative and qualitative differences among the compared forests resulted from the combined effects of light availability, the character of plant litter, agrotechnical works, as well as dispersal abilities of plant species.