Masters dissertation is foccused on survey through the issue of species diversity decrease and potentional taxonomic homogenization of forest vegetation at the landscape-scale in Slovakia using data acquired during general forest vegetation survey and its resampling in recent years. Many studies have explored species richness of forest vegetation at local spatial scales, though much less is known about temporal trends in diversity at landscape-scale, whereby the same lack of knowledge is within this issue in sub-montane and montane regions, whereas most resurvey studies carried out in Europe so far have focused on lowland forests. Moreover, processes of homogenization are poorly documented and understood within the ordinary managed high forests, which cover a significant part of Central Europe, Slovakia including. Therefore, the aim of the dissertation is to through the analyse of the empirical data observe, whether the processes of biodiversity decrease and homogenization caused by global environmental changes and which have been documented in lowland temperate forests so far do occur in submontane and montane region as well and thus if there could be found any trend in these vegetation changes within the altitude gradient.The first part of the thesis is focused on explanation of the issue of the loss of forest vegetation species diversity and its taxonomic homogenization along with the major initiating and driving factors particularly in the forests of Central Europe and therefore Slovakia as well. In the next part of the thesis I describe the methods of acquirement and processing of the empirical data for the analyse of the mentioned processes containing the whole spectrum of forest ecosystems of Slovakia. The last part is dedicated to interpretation of the results of the analyses along with the comparison with the existing knowledge on the issue.