Phytosociological alliances in the vegetation of arable fields in the northwestern Balkan Peninsula

A stratified dataset of 2426 releves of weed vegetation of arable fields of the Balkan Peninsula was analysed by cluster analysis. The major division in species composition was associated with the type of crop. This accords with the syntaxonomical and ecological pattern already detected for southeast Europe and is in conflict with the Central European classification that has appeared in recent years. Clusters resulting from numerical classification reproduced the majority of traditionally recognized phytosociological alliances (Oxalidion, Panico-Setarion and Eragrostion are associated with root crops, while Scleranthion, Caucalidion and Galeopsion with cereals). Galeopsion was grouped with some Caucalidion releves, which is not surprising since both consist of weed communities from cereals. Vernal communities form a separate cluster and indicate a special community type, which has been treated in some classification systems as a phenological aspect.