Importance of a multidisciplinary research is demonstrated by results obtained during the study of the tall grass Calamagrostis epigejos expansion in some alluvial meadow communities in South Moravia. Data on stand structure, above- and belowground biomass, uptake and losses of nutrients, plant litter decomposition and soil features were evaluated both for stands of two intact meadow communities and stands degraded by Calamagrostis epigejos in the attempt to find out what is responsible for the successful expansion of the tall grass. In specific conditions of the Dyje river alluvium, the deterioration of soil moisture regime and nutrients input occurred after the elimination of floods. Stands of Calamagrostis epigejos, in comparison with intact meadow stands, are characterized here by significant abiotic stress tolerance, given by higher water and nitrogen use efficiencies associated with stable and high biomass production. This is responsible for its competition success, expansion, as well as for the reduction of plant species richness and deterioration of soil conditions in such degraded meadows.