Abstract
The Mediterranean area is a key region to study relationships between vegetation dynamics, climate changes and human practices along the time. This region is characterized by high biodiversity, a significant sensitivity to climate changes and a complex and long human history. The Mediterranean Basin is thus a key region for understanding the respective impact of climate changes and human activities on ecosystems since the Holocene. The actual climate and biodiversity crisis raises this topic as a current and major issue that needs to be investigated and debated. This PhD study proposes to document environmental dynamics, climate changes and human practices during the last 15000 years around the Mediterranean Basin through a multiproxy approach including sediment geochemistry (XRF), pollen, Non-Pollen Palynomorphs (NPPs) and biomarkers molecular (branched Glycerol Dialkyl Glycerol Tetraethers or brGDGTs). Two mountainous areas poorly documented have been studied: the Lesser Caucasus with the Vanevan peat (Armenia) and the Apennines in Southern Italy with the Lake Matese. We investigated (1) modern pollen-vegetation relationships in Armenia and in the Matese Massif, (2) changes in vegetation and human activity around the Vanevan peat and the Lake Matese, (3) climate changes with water-level changes, molecular biomarkers “brGDGTs”, and pollen transfer functions (multi-method approach: Modern Analogue Technique, Weighted Averaging Partial Least Squares regression, Random Forest, and Boosted Regression Trees) and (4) relationships between vegetation dynamics, climate changes and human activities during the Lateglacial and the Holocene.At Vanevan, steppic taxa dominated during the last 9700 years and few trees have grown on shores of the Lake Sevan, even during the Mid-Holocene. At Matese, the vegetation was mainly steppic during the Lateglacial and the Early Holocene, although an increase of deciduous arboreal taxa was recorded during the Bølling–Allerød and finally Fagus and Mediterranean taxa develop during the Mid-Late Holocene. The Younger Dryas is well recorded in the Matese pollen assemblages. Climate reconstructions based on pollen and brGDGTs are complementary and they each have their advantages and biases. At Vanevan, climate reconstructions show an arid and cold Early Holocene, a more humid and warmer Mid Holocene, and a more arid and cooler Late Holocene. Several abrupt events have been detected at 6.2 ka, 5.2 ka, 4.2 ka, 2.8 ka and allow us to highlight the atmospheric processes in the Caucasus and the Near East. At Matese, the Bølling–Allerød is characterized by warm and humid conditions whereas the Younger Dryas is marked by cold conditions. The Holocene is firstly characterized by humid and warmer conditions followed by a slight decrease of precipitation and temperatures during the Mid-Late Holocene. Our study reveals a significant impact of abrupt climate changes on populations in the Near East and the Caucasus even for the recent periods. In the South Caucasus, the arid climate events are consistent with the population abandonment phases and changes in the agricultural practices around the Lake Sevan. In Southern Italy, anthropogenic indicators are less important, and the opening of forests is detected during the last 2800-2600 years and seem associated to human practices.