Formalized phytosociological classification of the Lake Trasimeno vegetation: an application of the Cocktail method.

Lake Trasimeno is a large (about 124 km2) shallow lake with significant fluctuations of water table, and a site of high conservation value (Site of Community Importance, Special Protection Area and Regional Park) in central Italy. Data about macrophytic, wetland, wet meadow, scrub, forest and ruderal vegetation of this area were collected during the last three decades by the present authors and other researchers and recently stored in the Anarchive database system. Vegetation classification was performed on a data set of 966 relevés using the Cocktail method. This method, designed to simulate the Braun-Blanquet approach, is largely based on expert knowledge, reflecting the field experience of the authors and the classifications published in the literature. In some cases, cluster analysis was also used to reveal the differences between communities with several generalist species, in particular within the class Molinio-Arrhenatheretea. All analyses were performed in the program Juice 7.0. The formal definitions were created using logical operators (AND, OR and AND NOT), combining species cover values and species groups. Sociological species groups and diagnostic species of the associations were determined using the phi coefficient of association. This method allowed to produce formal definitions for 79 communities included in 30 different alliances and 15 classes. The present work represents the first application of the Cocktail method in the Mediterranean area and Southern Europe. The number and distribution of the relevés are not sufficient for creating formalized definitions valid for a wide geographical area, but the Cocktail classification is largely in accordance with the expert-based classifications reported in the literature. It allowed to characterize different associations also in disturbed and floristically impoverished vegetation.