A phytosociological overview on the Sarcopoterium spinosum (L.) Spach communities in Italy

Sarcopoterium spinosum (L.) Spach dwarf-shrub vegetation occurring in the Italian territory is analysed in this contribution, with the aim of providing an updated syntaxonomic and ecological framework of these communities at national level. A dataset of 105 releves, from both literature and original data, was subjected to hierarchical clustering by Flexible-beta clustering algorithm with the Bray-Curtis dissimilarity index. Silhouette index was used to determine the best partition, and the phi coefficient for the identification of diagnostic species. To validate the results of clustering, crosstabs were implemented with the multivariate frequency distribution of the releves by groups and by ecological qualitative variables. Moreover, a Canonical Correspondence Analysis (CCA) with the bioclimatic variables was implemented. Seven groups were identified by cluster analysis, four of which are associations already known in literature, and three described here as new associations, namely: Ferulago geniculatae-Sarcopoterietum spinosi, Loto cretici-Sarcopoterietum spinosi, Pyro spinosi-Sarcopoterietum spinosi. For each association, diagnostic species and ecological validation are provided. As regards the syntaxonomic framework, the analysed communities fall within the Cisto-Micromerietea julianae Oberdorfer 1954 class and Cisto eriocephali-Ericion multiflorae Biondi 2000 alliance, except for the Pyro spinosi-Sarcopoterietum spinosi, included in the Quercetea ilicis Br.-Bl. ex A. Bolos et O. de Bolos in A. Bolos y Vayreda 1950, Oleo-Ceratonion siliquae Br.-Bl. ex Guinochet et Drouineau 1944.