Climate- and Human-Induced Vegetation Changes in Northwestern Turkey and the Southern Levant since the Last Glacial

Abstract

Northwestern Turkey and the southern Levant are key regions for studying vegetation and climate developments during migration phases of modern humans and the origin and expansion of agriculture. Both regions have a long history of different anthropogenic occupation phases, and the vegetation was sensitive to climate variations and anthropogenic influences. However, paleoenvironmental conditions in northwestern Turkey and the southern Levant are still insufficiently understood. Therefore, the main aim of this doctoral thesis was to investigate climate- and human-induced vegetation changes in both regions during the Last Glacial and Holocene.<br /> To fulfill this aim, palynological studies at three lacustrine archives were conducted. Pollen, non-pollen palynomorphs such as green algae and spores, and microscopic charcoal were extracted from sediment cores and microscopically analyzed. The sediment cores originated from Lake Iznik (northwestern Turkey), the Sea of Galilee (Lake Kinneret), and the Dead Sea (both southern Levant).<br /> Pollen data inferred from Lake Iznik sediments reveal the vegetation pattern in northwestern Turkey during the past 31 ka BP (thousand years before present). The vegetation changed between (a) steppe during stadials suggesting dry and cold climatic conditions, (b) forest-steppe during interstadials implying milder and more humid climatic conditions, and (c) oak-dominated mesic forest during the Holocene indicating warm and humid climatic conditions. A distinct succession of pioneer trees, cold temperate trees, warm temperate trees, and Mediterranean trees occurred since the Lateglacial. Rapid climate changes reflected in vegetation shifts correlate with Dansgaard-Oeschger events (DO-4, DO-3, and DO-1), the Younger Dryas, and most likely the 8.2 ka event. The distinction between climate- and human-induced vegetation changes is challenging during early settlement phases. Nevertheless, evidence for human activity consolidates since ca. 4.8 ka BP (Early Bronze Age). Forests were cleared, and cultivated trees, crops, and secondary human indicator taxa appeared. Subsequent fluctuations between extensive agricultural uses and regenerations of the natural vegetation occurred.<br /> The palynological investigation at the Dead Sea provides insights into the vegetation history of the southern Levant between ca. 88 and 9 ka BP. The pollen record from the Sea of Galilee yields additional information for 28–22 ka BP, when the Sea of Galilee rose above the modern lake level and temporarily merged with Lake Lisan, the Last Glacial precursor of the Dead Sea. A mixture of Irano-Turanian steppe communities, Saharo-Arabian desert vegetation, and Mediterranean woodland components occurred in the Dead Sea region during the Last Glacial. Pollen proportions of these three biomes changed over time mainly in response to changes in effective moisture (available moisture for plants). During the early Last Glacial (marine isotope stage (MIS) 5b/a and early MIS 4), the amount of Saharo-Arabian desert components was higher relative to later phases indicating low effective moisture. An increased proportion of Irano-Turanian steppe vegetation and Mediterranean woodland elements during the late MIS 4, MIS 3, and MIS 2 suggest more effective moisture. MIS 2 was the coldest period of the investigated timeframe as indicated by a change in arboreal taxa. An assessment of the vegetation and climate gradients in the southern Levant during MIS 2 is possible by comparing the Sea of Galilee and Dead Sea pollen datasets. The well-dated and high-resolution pollen record from the Sea of Galilee suggests that steppe vegetation with dwarf shrubs, grasses, and other herbs predominated in northern Israel during 28–22 ka BP. In contrast to the Holocene, dense Mediterranean woodland did not cover the surroundings of the Sea of Galilee. Thermophilous trees were probably patchily distributed in the whole study area. The gradient of effective moisture between the Sea of Galilee and the Dead Sea/Lake Lisan was not as strong as today. The Dead Sea region witnessed several environmental changes during the Lateglacial and early Holocene caused by climatic variations and/or anthropogenic influences. After these rapid and pronounced changes, a considerably different ecosystem with sparse Mediterranean woodland, high fire activity, and strong catchment erosion prevailed in the Dead Sea region.<br /> While the results for northwestern Turkey are largely in line with previous regional vegetation and climate studies, previous investigations from the southern Levant concluded contrasting environmental scenarios for the Last Glacial and early Holocene. Thus, the new palynological results for the southern Levant apparently contradict some of the previous hypotheses. Therefore, factors influencing the pollen assemblage and the plant cover are discussed.<br /> The three palynological investigations provide insights into long-term and short-term variations of the paleoenvironment in northwestern Turkey and the southern Levant since the Last Glacial. They contribute to our understanding of interactions between vegetation, climate, and humans in the Eastern Mediterranean. This knowledge is not only essential for reconstructing the migration history of modern humankind but also helps to evaluate effects of current and future climate changes on the environment.