Classification of dry grassland vegetation in Denmark

A hierarchic classification of Danish semi-natural grassland vegetation on well-drained soils is presented. TWINSPAN was used for clustering of 614 sa mples of grassland vegetation showing floristic gradients and turnover in s pecies composition in more dimensions. The optimal hierarchic level of clus tering was determined by indicator species analysis. The classification was interpreted in terms of variables relating to abiotic environment and vege tation structure and to major ecoclines previously identified by gradient a nalysis. The 12 final clusters were compared to syntaxa of formal phytosoci ology and to communities in the British Vegetation Classification. Criteria for achieving floristically homogeneous clusters without sacrificing the e cological interpretability and validity of the clusters in time and along g eographical gradients are discussed.