The alluvial vegetation of the Po river in the central-west Padana Plain (Po Plain-Northern Italy).

This is a phytosociological study of vegetation communities occurring along the Po river in the Central-West Padana (Po) Plain. Herbaceous formations on the river bed, Salix alba woods and an elm-oak wood were analyzed. Ten vegetation types were identified in the study area. It was possible to phytosociologically define and characterize the associations of some of them, such as the Polygono hydropiperis-Bidentetum tripartitae, the Polygono-Xanthietum italici, the Salicetum albae and the Querco- Ulmetum minoris. The others were physiognomically and ecologically individual communities, often with few species, which I studied in any case because they represent initial phases for more developed woody vegetation or evidence of past use of the territory, such as the Artemisia verlotiorum community. I characterized them at the alliance level (Agropyron repens community, Artemisia verlotiorum community) or the class level (Koelerio-Corynephoretea communities and Galio-Urticetea communities). The syntaxonomic position is not yet clear for the pioneer xerophilous community and the neophyte community. The analysis of the species compositions, the biological spectra, the chorological spectra, the layer covers, the layer heights and the substrata of the identified vegetation types allowed their ecological and dynamic features to be defined. Each vegetation type occupies a different position with respect to the river bed and thus has a different relationship with the action of the river. Polygono hydropiperis-Bidentetum tripartitae and Polygono-Xanthietum italici are the communities most influenced by the water course, being submerged every year and even several times in one year. The Agropyron repens community, the Artemisia verlotiorum community and the Galio-Urticetea communities are more stable than the Polygono—Bidentetum and Polygono-Xanthietum, being less disturbed by the river and showing higher percentages of hemicryptophytes, geophytes and nanophanerophytes. The Salicetum albae is submerged by the river during big spates; the Querco-Ulmetum minoris is submerged by the river only during exceptional spates. The Koelerio-Corynephoretea communities and the pioneer xerophilous community occupy the gravelly fluvial terraces beyond the influence of the river