Syntaxonomy and community ecology of mires in the Rhaetian Alps (Italy)

On the basis of cluster analysis of phytosociological releves, the mire veg etation in the Rhaetian Alps was arranged in sixteen plant communities synt axonomically included in four classes. The class Potametea was characterise d by two different plant communities of perennial hydrophytes rooting in th e bottom sediment of lakes (communities of Potamogeton alpinus and Potamoge ton natans, respectively). The class Littorelletea included two plant commu nities characteristic of shallow water bodies (Callitricho-Sparganietum and community of Ranunculus reptans). The class Scheuchzerio-Caricetea nigrae included small-sedge swards and quaking rafts spanning a broad range of hyd rochemical conditions with 8 plant communities and 5 alliances. The allianc e Rhynchosporion albae included the vegetation of hollows and shallow ponds in nutrient-poor mires, with the Caricetum limosae and a community of Erio phorum angustifolium. The alliance Caricion lasiocarpae, including vegetati on of hollows and pools in intermediate mires, was represented by an only a ssociation, the Caricetum rostratae. The alliance Caricion nigrae included sedge-swards in acid fens, with the Caricetum nigrae, the Caricetum pauperc ulae, the Menyantho-Sphagnetum teretis and the Eriophoretum scheuchzeri. Th e alliance Caricion davallianae included rich fen vegetation with an only a ssociation, the Drepanoclado-Trichophoretum cespitosi. The C ari cion atrof usco-saxatilis included only the Caricetum microglochinis, a carbonate fen association in the alpine vegetation belt. The class Oxycocco-Sphagnetea co rresponded to the vegetation of Sphagnum hummocks in ombrogenous mires, wit h three associations: the Sphagnetum magellanici, the Eriophoro-Trichophore tum cespitosi and the Pinetum rotundatae. The habitat in all plant communit ies was defined on the basis of pH and electrical conductivity of porewater , reflecting the degree of inflow of geogenous water. The role of elevation in affecting the distribution of plant communities was particularly clear for the associations of the class Oxycocco-Sphagnetea, which were mainly de veloped in the lower sub-alpine vegetation belt, and for the Eriophoretum s cheuchzeri, confined to the alpine vegetation belt.