Vegetation dynamics of the East- European forest-steppe since the Late Glacial: climate, human and fire impact
Dissertation
Datum der mündl. Prüfung:2023-03-21
Erschienen:2024-03-11
Betreuer:Prof. Dr. Hermann Behling
Gutachter:Prof. Dr. Daniela Sauer
Gutachter:Dr. Lyudmila Shumilovskikh
Dateien
Name:Thesis_merged_library.pdf
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Zusammenfassung
Englisch
While many studies have documented changes of the northern latitudinal forest limit in Europe and its drivers, little is known about the southern latitudinal limit of the forest towards the steppe in Eastern Europe. Characterized by fertile chernozem soils, the region has been consequently anthropogenically changed, with more than 80% of the area used as cropland by the year 2000. Therefore, it is hard to estimate the natural extension of the forest-steppe zone and to predict the response of the ecosystems to the global warming in the future. For sustainable management strategies, nature conservation and land use should be based on the knowledge of the natural vegetation of the area, which can be obtained by palaeoecological studies. This work contributes to the understanding of the vegetation dynamics of the East-European forest-steppe due to climate changes, human impact and fires since the Late Glacial period. The results of multi-proxy analyses of four sediment cores obtained from the northern, central and southern parts of the ecotone during the expeditions of 2009-2013 are presented in the dissertation. Combining all available records, we reconstruct the forest cover using the modern analogue technique and evaluate possible shifts in the forest limit and the character of the ecotone since the postglacial. With the use of transfer functions, we explore potential climate forcing that may have changed the vegetation in the ecotone during the postglacial. The research shows that the vegetation of the East-European forest-steppe is highly sensitive to moisture availability caused by the northern hemispheric climate changes. Thus, the stadial periods of the Late Glacial caused the steppe spread while forest-steppe was developing during the interstadials within the study region. The region became an ecotone between forest and steppe zones by ~8 cal. kyr BP after the Holocene warming ~11.7 cal. kyr BP allowed the spread of forest into steppe. The spread of the broadleaf trees coincided with decreasing summer insolation and temperatures in the late mid-Holocene and late Holocene lowering evapotranspiration values and increasing the amount of available moisture. During the late Holocene the region became entirely forested including its southern limits. The southern treeline is extremely sensitive to human activities. With the development and spread of agriculture, local societies induced deforestation and fires to clear the land. In the last 800 yrs the area of the ecotone became deforested reaching the minimum forest cover in the 17th century. The conversion of the forest-steppe into an agrarian steppe left over only very small patches of semi-natural vegetation today. Considering the current global warming the southern tree line is likely to shift northwards bringing the area to the mid-Holocene conditions. Lower aridity index and therefore moisture availability will increase the risks of droughts affecting agriculture in the region.
Keywords: Palaeoecology; pollen records; ; Eastern Europe; forest-steppe; late glacial; Holocene; vegetation history; limate dynamics