Phd in ENVIRONMENTAL AND EVOLUTIONARY BIOLOGY

Thesis title: Pollen analysis of Late Holocene marine sediments from the Central Mediterranean Sea

This thesis aims to reconstruct the Late Holocene vegetation dynamics of SE Sicily in relation to climatic oscillations and human activity, in the frame of the environmental history of the Mediterranean region. Pollen analysis was performed from two marine sedimentary sequences from the Sicilian Channel, forming the composite record ND2 that spans the last 3000 years. This record is complemented by a marine pollen record from the Gulf of Gaeta, in south-central Tyrrhenian Italy, where Non-Pollen Palynomorphs analysis was carried out. A multidisciplinary approach including marine palynology, palaeoclimatology, and historical ecology was used to identify the sources of environmental variability, whether anthropogenic or natural, and their possible interplay through time. These records have been framed in a broader picture of vegetational changes across the Mediterranean Basin, which has been investigated in relation to the 4.2 ka event. The new high-resolution marine pollen record ND2, located in the heart of the Mediterranean Basin, provides new insights into the regional vegetation dynamics of the last few millennia, contributing to a better understanding of the mesoscale processes of hydroclimatic variability influencing forest ecosystems at a millennial to centennial-scale. Recurrent patterns of expansion and reduction of woodland appear to correspond to changes in atmospheric circulation related to the Bond events. A decrease in forest cover at the Bronze Age-Iron Age transition, corresponding to the Bond event 2 and the Homeric Solar Minimum, is consistent with the so-called “2.8 ka event”. A similar forest cover reduction was found at the time of Bond event 1, during the so-called Late Antique Little Ice Age (LALIA), and during the Bond event 0 coinciding with the well-known Little Ice Age (LIA) and the relative Wolf, Spörer, Maunder, and Dalton solar minima. An abrupt forest decline is also observed in correspondence to the Oort solar minimum during the Medieval Climate Anomaly (MCA). The striking coincidence of these vegetation changes with all the Grand Solar Minima of the Late Holocene suggests that hydroclimatic changes were influenced by the localization, migration, and stability of atmospheric systems in response to solar activity. At the same time, the regional reconstruction of past vegetational dynamics shown by the ND2 record reflects the socio-economic processes and past land-use practices reported by historical documents, offering new insights into the vegetation history of SE Sicily. For example, the vegetation history of the last 400 years reveals a remarkably stable landscape, preserved by traditional land-use practices that have persisted through the long-lasting feudal history of Sicily and its economic system and the productive organization. Increases in Olea cultivation correspond to the Greek colonization of the island and to the Byzantine–Arabic period. A new spread of olive took place in the last two centuries and especially during the post-war industrialization, when a marked change in land-use completely changed the agro-silvicultural practices of the region. The pollen and NPPs record from the Gulf of Gaeta represents cultural and climate phases (Roman Period, Dark Ages, Medieval Climate Anomaly, Little Ice Age, and Modern Period) of the last 2000 years. The human impact, associated to stockbreeding activities, fire incidence, and silvicultural practices, produced a general and progressive decline of natural forest ecosystems. However, irrespective of the societal cultural phase, forest declines occurred when negative NAO oscillations induced dry climate, especially during sunspot minima. The rapid vegetational changes detected over the last 3000 can be interpreted in the light of a broader context of bioclimatic changes emerged from the analysis of tree cover change during the 4.2 ka event over the entire Mediterranean Basin. This analysis revealed a coherent system of ecological processes of opposite polarity at a sub-continental scale, characterized by a sign-switching ecological pattern. This coherent system of ecological configurations was possibly determined by the reorganization of the atmospheric modes. The discovery of ecological processes of opposite polarity at a sub-continental scale sheds new light on geographical patterns of past and present environmental vulnerability to rapid climate change in the Mediterranean Basin.