The order Quercetalia virgilianae: a new proposal for the classification of semi-deciduous forests in the Mediterranean and sub-Mediterranean area.

The semi-deciduous oaks belonging to Quercus pubescens s.l. group (Q. congesta C. Presl, Q. virgiliana (Ten.) Ten., Q. dalechampii Ten., Q. amplifolia Guss. and Q. leptobalanus Guss.) are widespread in the Italian Peninsula, Sicily, Sardinia and along the southern coasts of the Balkan peninsula and more generally in the whole Mediterranean area, especially in the transition zone between the temperate and Mediterranean macrobioclimate identified by the sub-mediterranean variant (Brullo et al., 1999). These forests are currently expanding rapidly because of the decreased anthropic exploitation. The syntaxonomic classification of these forest typologies is quite critical, because their floristic composition includes a rich contingent of thermophilous species traditionally belonging to the class Quercetea ilicis alongside species more mesophilous typical of the thermophilous forests of the class Querco-Fagetea. The importance of these two groups of species varies with latitude and distance from the sea, determining various forms of transition. Therefore, some associations dominated by Quercus virgiliana are included in the order Quercetalia ilicis – the basifilous ones in the alliance Fraxino orni-Quercion ilicis, while the acidophilous ones in the alliance Erico- Quercion ilicis – while other associations are classified in the order Quercetalia-pubescenti-petraeae - suballiance Lauro-Quercenion pubescentis of the Carpinion orientalis in central Italy and in the alliance Pino calabricae-Quercion congestae, suballiance Quercenion virgilianae in southern Italy. The aim of the present study is to demonstrate that the different types of oak forests dominated by Q. virgiliana, Q. amplifolia and other species of the same group belong to the new order named Quercetalia virgilianae. The statistical elaborations carried out support this choice and are crucial in order to determine the hierarchical lower ranks and identify diagnostic species. The proposal of the new order is part of the project started with the implementation of Prodrome of the Italian vegetation (Biondi et al. 2014) that, relying on a set of core principles (Biondi et al., 2015), aims to give importance to the syntaxa typical of the sub-Mediterranean area, where phytocoenotic biodiversity is very high, but not enhanced by the current syntaxonomic classification. The importance of highlighting the originality of woodlands with Quercus virgiliana of the sub- Mediterranean zones coincides with the conservation purposes of the Habitats Directive and in particular the recognition of the existence in Italy of the habitat 91AA.