How do environmental variables shape plant species diversity and composition in beech forests of Central Slovakia?

European beech forests are an important component of natural vegetation in submontane and montane areas of Central Europe. Although floristic variability of their plant communities has been relatively well described, there is no universal set of environmental predictors shaping their vegetation structure. We sampled vegetation and environmental data associated with soil, light, topography and climate in beech-dominated stands of central Slovakia in order to determine how these factors act on plant species diversity and composition variability. We recorded all vascular plants for each plot with uniform size (20 × 20 m). Redundancy analysis (RDA) with forward selection procedure was used to test the species composition-environmental relationship. Generalized linear model (GLM) assessed the importance of environmental variables as predictors of species richness. European beech forests were in general species-poor with a mean of 15 (range 6–30) plant species per plot. Three factors (soil pH, total soil nitrogen, canopy openness) were found to be responsible for species composition variation in RDA. Their marginal effect was 30.2%, but only soil pH (8.3%) and total soil nitrogen (5.9%) contributed to the explained variance of pure effect. GLM identified positive linear effect of four variables (soil pH, altitude, canopy openness, radiation) on species richness of vascular plants. The strongest predictors were soil pH and altitude, but all factors included in the model jointly explained 57.3% of variation in species richness data.