The Bachelor's work is focused on issue of degradation of plant species diversity in temperate oak forests of Slovakia. The intention of the work is to make clearer and sumarize actual knowledge about the topic, as well as all the other related information. Moreover, the aim of the work is to analyze the issue and point out to wider context. Due to global environmental change and change in land use management ecosystems of temperate lowland forests suffer from thermophilization and eutrophication resulting in homogenization of forest undestorey vegetation. Homogenization means decline of plant diversity forest plant species typical for oak woods of temperate zone. First chapter of the work is intent on explanation of the issue. It is devoted to biodiversity, its loss and causes of the loss of plant diversity of oak woods in Slovakia, which are: change in land use management, increased loads of nitrogen and global climate change. The second chapter is devoted to possible solutions of loss of species diversity based on information obtained through manipulative experiments. Also, I analyze the manipulative experiments carried out in abroad. Finally, in the last chapter I represent study accompanied by manipulative experiment, which takes place in Slovakia under the auspices of Technical University in Zvolen.In concusion I sumarize all of the acquired knowledge about the theme and I evaluate the solution of the problem. Key words: plant diversity, biodiversity loss, global environmental changes, vegetation restoration