The content of this thesis is focused on the study of competitive relations in beech stands. The beech (Fagus sylvatica) forms homogenous stands in the zone of their ecologically-productive optimum, which they represent leading competitor limiting understorey vegetation. The selection of the studied stands was carried out on the volcanic mountain of Javorie, spreading over the volcanic bedrock. One of the observed objects was also the relationship of species richness and altitude. This relationship shows an inverse unimodal curve with a minimal number of plant species at the center of the curve, precisely on the volcanic bedrock. The data needed for analyzing and evaluating relationships were collected at different height ranges, the range of which them was set at 100 m. After collecting the data, mainly representing samples of underground biomass and phytosociological register, the fine roots were sorting according to the thickness level, contained in the soil samples, separately for each plots were then considered to determine the amount of underground biomass. In the analysis, the plant species observed by describing the plots were also processed electronically in program Turboveg. The sorted data were then processed in the table, which the results were interpreted by using graphs. The results evaluated several relationships, that affect the amount of underground biomass of beech, as well as the factors affecting the species diversity of plants. Most of the results, such as the relationship of the basal area and the number of fine roots, or the competitive relationship between tree quantity and species richness has been fulfilled as expected, except for some exceptions. We suppose that result of some deviations it is mainly the fact that, the necessary number of data has not been collected on the terrain, which in our case means the need for a larger number of plots. In the discussion, the results are evaluated and found in some cases very similar matches to claims of other authors.