On the origin and evolution of the Mediterranean dry grasslands.

A synthesis on the functional types of Mediterranean dry grasslands is outlined. Three different types are outlined: wintergreen perennial dry grasslands, wintergreen ephemeral dry grasslands, summergreen perennial dry grasslands. The first type is the most primitive, including several relict species, often characterized by very disjoint, sometimes anfi-saharian distribution ranges. The second type is resulting from an evolutionary trend towards short-lived life strategy, triggered by climatic and topographic perturbations that affected the Mediterranean region in the Plio- and Pleistocene. The third type, only marginally occurring in the Mediterranean region, is deriving from Holarctic and Eurasian elements, that probably colonized the Mediterranean lands during the Pleistocenic dry interglacial periods. The evolutionary success of the Mediterranean dry grasslands have been ensured by the combination of high topographic diversity and multiple land-use patterns. Their existence is based on a dynamic long-term flow equilibrium, depending on cyclic perturbations, that let them to acquire a long-term evolutionary metastability.