Italian black alder swamps: Their syntaxonomic relationships andoriginality within the European context

The aim of this study is to present a phytosociological survey of the Italian Alnus glutinosa-dominated swamps (Alnion glutinosae). The analysis highlights the occurrence of the following associations: Corno hungaricae-Alnetum glutinosae and Carici elatae-Alnetum glutinosae (northern Italy), Hydrocotylo-Alnetum glutinosae and Scrophulario umbrosae-Alnetum glutinosae (central and southern Italy). Carici elongatae-Alnetum glutinosae, which is widely distributed in central and northern Europe, has so far only been identified in a narrow area of the western continental sector of the Po plain; elsewhere, this association is replaced by communities generally characterized both by the lower expression of species whose main center of distribution is in the central-northern sector of Europe, and by the presence of differential entities. The comparison of data from southern, central and northern Europe confirms the syntaxonomic autonomy of most of the Italian Black Alder swamps. Moreover, the study reveals the existence of a north-to-south phytogeographic gradient, according to which the sub-boreal phytocoenoses are gradually being replaced by the central-European temperate communities as well as by the last southern European phytocoenoses occurring in the temperate and Submediterranean/Mediterranean contexts.