The Nardus-rich communities in the northern Apennines (N-Italy): a phytosociological, ecological and phytogeographical study

Secondary grasslands dominated by Nardus stricta are an anthropogenic vegetation type that occurs widely through the Europe from lowlands to mountains. These communities have been recently recognized by the European Community as a habitat of priority interest. The aim of the study is to perform a detailed and complete phytosociological scrutiny of this vegetation in the northern Apennines. Further aims are to detect the factors controlling the floristic variation within these communities and to analyse the variations of Nardus grasslands along a latitudinal gradient from the northern Alps to the southern Apennines. We processed a set of 134 phytosociological releves from the northern Apennines through a cluster analysis based on Kendall's tau dissimilarity measure. Results showed the occurrence of two different associations of Nardus grasslands (Carlino caulescentis-Nardetum strictae and Violo ferrarinii-Nardetum strictae). Relations between their floristic composition and environmental variables were detected through Redundancy Analysis. The matrix of habitat factors included topographic variables and variables derived from Ellenberg's indicator values. Elevation was the factor explaining most of the floristic variation. From the comparison of 44 synoptic tables from the Alps, Carpathians and Apennines, processed through a NMDS ordination, we detected two main phytogeographic and ecological thresholds along the latitudinal gradient.