Costal pine-oak glacial refugia in Mediterranean basin: a biogeographic approach based on charcoal analysis and spatial modelling

During the glacial episodes of the Quaternary, European forests were restricted in small favorable spots, namely refugia, acting as biodiversity reservoir. These climate refugia have a major role in explaining modern patterns of biodiversity and species distribution. As a general rule the Iberian, Italian and Balkan peninsulas, have been identified as the main glacial tree refugia areas in Europe. In this study, set in a coastal cave of the Cilento area (SW Italy), we estimate the consistency of the last glacial forest and the tree species composition in this region embedded in the core of Mediterranean basin at 7 time frames, spanning from the last Pleniglacial and Lateglacial. Charcoal analysis was carried out in 7 archaeological layers. A palaeoclimatic modelling approach was coupled to the taxonomic identification of charcoal fragments, to refine the precision of the tree species reconstruction. Our results show that meso-thermophilous, forest was able to survive in this costal sector in the core of Mediterranan Basin during the LGP (from ~36 ka cal BP), proving that this area played an important role as a reservoir of woodland biodiversity in which Q. pubescens was the most abundant component, followed by a wide variety of deciduous trees and P. nigra. Charcoal data also evidence the crucial role of this coastal strips, acting as a reservoir for temperate warm tree taxa Tilia, Carpinus and Sambucus, in Late glacial period, in Mediterranean area. The Maxent model, provided a useful complement to the palaeoecological study, both refining charcoal evidence and offering a less subjective hypothesis concerning past geographic distributions of Pinus species in the LGM.