Syntaxonomy and community ecology of mires in the Rhaetian Alps (Italy)
Gerdol, Renato; Bragazza, Luca
On the basis of cluster analysis of phytosociological relevés, the mire vegetation in the Rhaetian Alps was arranged in sixteen plant communities syntaxonomically included in four classes. The class Potametea was characterised by two different plant communities of perennial hydrophytes rooting in the bottom sediment of lakes (communities of Potamogeton alpinus and Potamogeton natans, respectively). The class Littorelletea included two plant communities 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 hydrochemical conditions with 8 plant communities and 5 alliances. The alliance Rhynchosporion albae included the vegetation of hollows and shallow ponds in nutrient-poor mires, with the Caricetum limosae and a community of Eriophorum angustifolium. The alliance Caricion lasiocarpae, including vegetation of hollows and pools in intermediate mires, was represented by an only association, the Caricetum rostratae. The alliance Caricion nigrae included sedge-swards in acid fens, with the Caricetum nigrae, the Caricetum pauperculae, the Menyantho-Sphagnetum teretis and the Eriophoretum scheuchzeri. The alliance Caricion davallianae included rich fen vegetation with an only association, the Drepanoclado-Trichophoreturn cespitosi. The Caricion atrofusco-saxatilis included only the Caricetum microglochinis, a carbonate fen association in the alpine vegetation belt. The class Oxycocco-Sphagnetea corresponded to the vegetation of Sphagnum hummocks in ombrogenous mires, with three associations: the Sphagnetum magellanici, the Eriophoro-Trichophoretum cespitosi and the Pinetum rotundatae. The habitat in all plant communities 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 developed in the lower sub-alpine vegetation belt, and for the Eriophoretum scheuchzeri, confined to the alpine vegetation belt.