Upper Pleistocene and Late Holocene vegetation belts in western Liguria: an archaeopalynological approach

This study presents a new approach of local vegetation history based on pollen analyses of four sediment profiles from two archaeological sites located in western Liguria (northwest Italy). Statistical analyses (principal components analyses: PCA) were used to provide four theoretical patterns on vegetation distribution in Mediterranean belts during the Upper Pleistocene and the Late Holocene. PCA were mainly applied to elaborate vegetation assemblages such as Mediterranean pre-forest unit, evergreen woodland, or alluvial forest, and to replace these groups in a local area according to edaphic factors. The pollen data showed 10 vegetation assemblages, extending from the seashore arid zone to the Ligurian mountains humid/per-humid zones. These groups are distinct arboreal or non-arboreal formations and give pictures of the vegetation from the arid coastal herbs located on the seashore to the deciduous forest developed at low altitude. The statistical data were also used to develop PCA synthetic pollen diagrams (PCAsd). In Liguria, PCAsd showed the weight of Mediterranean vegetation during the last Interglacial whereas the early Weichselian glacial is marked by the extent of the steppe landscape. From the last Interglacial to the Lower Pleniglacial, the climate was characterized by a significant increase of drought from the coastal zone to the Ligurian relief, together with an increase of moisture in altitude. The coastal warm and dry Interglacial climate turned to cool and humid during the beginning of the Weichselian glacial, and to colder and drier during the Lower Pleniglacial.