20,000 years of interactions between climate, vegetation and land use in Northern Greece

Detailed knowledge about the history of vegetation, fire and land use is scarce in Northern Greece. We analysed lake sediments from Limni Zazari (Northern Greece) to reconstruct the past local vegetation and fire history with a special focus on land use and its impacts on erosion and lake eutrophication. Our data suggest a rather dense steppic vegetation after ca 20,000 cal BP (18050 cal BC). Forest expansion with Pinus sylvestris and admixed Quercus pubescens started around 14,500 cal BP (12550 cal BC). After the onset of the Holocene, mixed deciduous sub-mediterranean oak forests expanded, accompanied by rapidly decreasing soil erosion rates and increasing aquatic biological productivity. Pollen of cereals and Plantago lanceolata suggests continuous farming activities in the region after 8,200 cal BP (6250 cal BC), in agreement with archaeological evidence. Fairly closed mixed pine-oak forests dominated the landscape until ca 3,500 cal BP (1550 cal BC) that were only temporarily reduced during the Neolithic around 7,100 and 6,500 cal BP (5150 and 4550 cal BC). Land cover changes and aquatic biogeochemistry were closely linked during this period. Forest phases corresponded to lake eutrophication and hypolimnetic anoxia (meromixis), whereas during periods of deforestation (e.g. around 8,200 cal BP/6250 cal BC) soil erosion rates and lake mixing increased, while aquatic productivity decreased. After 3,500 cal BP (1550 cal BC) humans disrupted forests and open land vegetation expanded (e.g. Artemisia, Rumex-type, Cichorioideae, Chenopodiaceae). With the onset of the Iron Age (ca. 3,050 cal BP/1100 cal BC) grassland communities expanded massively and pine-oak forests gradually declined. Anthropogenic pressure on forests increased even more during the past 500 years. Finally, forest recovery during the recent decades led to decreased erosion and increased lake productivity. We conclude that over the millennia, intense pastoral and arable activities shaped both aquatic and terrestrial environments, ultimately creating a humanized vegetation mosaic in which the original natural mixed deciduous oak forests only form relict stands. Future climate warming and decreasing anthropogenic pressure may release a rapid spread of mixed deciduous oak forests around Limni Zazari.