Ecological causes of the floristical differentiation of Carici pilosae-Fagetum and Dentario bulbiferae-Fagetum associations have been studied. Therefore the phytocenological releves and macromorphological, physical and chemical properties of typical cambisols were compared on the selected parallel plots. From the geobiocenological point of view, the both phytocenoses belong to the 3rd forest vegetation tier, mesotrophic order of geobiocens, group of forest types Fagetum pauper inferiora (in the sense of Zlatnik, 1959) and types of geobiocens Carex pilosanudum and Dentaria bulbifera-nudum (in the sense of Hancinsky, 1972). These phytocenoses do not differ substantially from each other by values of soil reaction and content of available nutrients (pH(H2O) = 5.2-5.6, pH(KCl) = 4.2-4.6, K(Sch) = 290-340 mg.kg-1, P(B.K) = 84-85 mg.kg-1 in topsoil) and neither by their position in the framework of the mesotrophic edaphic-ecological order of geobiocens. Greater differences were found in values of the soil water capacity in favour of the association Dentario bulbiferae-Fagetum. It was determined by means of a reduced (by volume of skeleton) soil thickness and of a maximum capillary capacity of the soils. In comparison with a maximum water capacity of soils situated on the border of segments of the nudal beech forests and hydrically (even by the growth) limited oak forests of the 3rd forest vegetation tier (in case of loamy soils 120-150 mm, in dependence on a slope orientation) the values determined in a soil of the association Carici pilosae-Fagetum were only slightly higher (185 mm). Therefore, it seems that the beech forest suffers from lack of water when the annual precipitations are low. As a result the shading ability of a beech is lowered, the more light demanding tree species (including Quercus dalechampii) occur in a stand and the sedge-grasses in a herb layer.