Mid-Holocene vegetation history of the central Mediterranean

This paper provides a synthesis of available palynological data from central Mediterranean lacustrine records, studying the causes of the important vegetation changes which occurred in the mid Holocene. They are illustrated by seven well-dated records, lakes Accesa, Mezzano, Vico, and Pergusa in Italy, Maliq, Voulkaria and Malo J. in the Balkans. A good tool for disentangling climate change and human impact is the combined interpretation of pollen percentage and concentration/influx data. Pollen concentration/influx drops are an indication of increased erosion in the catchment, mainly ascribable to forest reduction. There is no doubt that major synchronous changes could not have been caused by humans alone. Many southern European records show substantial differences between early- and late-Holocene vegetation, suggesting a general evolution from wetter to drier climatic conditions, in agreement with arid phases recognised by other, independent palaeoclimatic methods. Other pollen records show a different trend. The role of changing seasonality seems important for this region of the Mediterranean. Precipitation seasonality increased during the early to mid Holocene with winter precipitation attaining a maximum, and summer precipitation a minimum. At least three rapid climate events with changes in plant biomass are in evidence: an abrupt and short change around 8200 yr BP, another one centred around 6000 yr BP, and one soon after 3000 yr BP. From the beginning of the Bronze Age (c. 4400 yr BP in this region) human impact overlapped with a climate change, probably bipartite, towards dryness. Our results show that this aridification trend began around 8000 yr BP, and culminated around 4000 yr BP.