THE ERICACEOUS DWARF SHRUBLANDS ABOVE THE NORTHERN APENNINE TIMBERLINE (ITALY)

Ericaceous dwarf shrublands which are settled above the timberline oil a long stretch of the Northern Apennines were studied with the Braun- Blanquet approach. Phytosociological data were numerically treated thr ough the following steps: 1) species ranking by a variance criterion; 2) classification of releves and species based on the reduced species set; 3) characterization of the resulting types by analysis of concent ration. The following three main vegetation types were recognized: a) Empetro-Vaccinietum gaultherioidis subass. juncetosum trifidi, which i s the shrubland corresponding to the sites with less suboceanic climat e; b) Rhododendretum ferruginei, which is a very rare, sometimes fragm entary community settled on small areas, and c) Hyperico richeri-Vacci nietum gaultherioidis, which corresponds to the sites with suboceanic climate. The first two have a high similarity with the corresponding v egetation types from the Alps and are their most southern known exampl es in Italy The third type is typical of the Northern Apennines and ha s only fragmentary examples southwards on this chain. On rare and smal l areas two impoverished plant communities which are related to the Em petrum-Vaccinietum were also described: Thymus alpigenus/Vaccinium gau ltherioides community, on summit windy sites with rocky soils, and Pol ygonatum verticillatum/Vaccinium gaultherioides community on summit si res on low mountains towards the north-western end of the Northern Ape nnine dwarf shrublands. The summit dwarf shrublands of the Northern Ap ennines are dominated by boreal and south-European orophytes, to whom arctic-alpine taxa are added into the Empetro-Vaccinietum gaultherioid is subass. juncetosum trifidi. At high syntaxonomical levels the Empet ro-Vaccinietum gaultherioidis subass. juncetosum trifidi and the relat ed impoverished plant communities are to be included in the alliance L oiseleurio-Vaccinion. The Rhododendretum ferruginei and the Hyperico r icheri-Vaccinietum gaultherioidis belong to the Rhododendro-Vaccinion. Such dwarf shrublands are chiefly related to differences in the snow cover duration and height. All the plant communities stress the phytog eographic connection among the Northern Apennine summit vegetation and the subalpine vegetation belt of the Alps.