Early Holocene local environments, fire regimes, and land use signals inferred from multi-proxy palaeoecological records at two microregions of Southwestern Germany

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URI: http://hdl.handle.net/10900/137195
Dokumentart: Dissertation
Date: 2023-03-01
Language: English
Faculty: 7 Mathematisch-Naturwissenschaftliche Fakultät
Department: Geographie, Geoökologie, Geowissenschaft
Advisor: Junginger, Annett (Dr.)
Day of Oral Examination: 2022-11-16
DDC Classifikation: 550 - Earth sciences
Keywords: Holozän , Holzkohle , Pollen
Other Keywords:
paleoenvironmental reconstruction
fire regimes
land use
License: Publishing license excluding print on demand
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High-resolution multi-proxy palaeoecological studies are one of the best means for reliably tackling the question of how climate, ecosystem dynamics, and human agency are interrelated in a long-term perspective. When applied in areas with well-studied and precisely dated past settlement and land use history, such multi-proxy analyses offer valuable novel insights on climatic and anthropogenic agency in a given landscape. Disentangling those two main driving factors is key to shaping past vegetation and environments. Moreover, detailed local information on past ecosystems obtained by palaeoecological research is highly relevant to understanding how ancient human populations adapted to the environmental change, how far they exploited natural resources, and how their land-use strategies affected the landscape. The current thesis involves a multi-proxy palaeoecological study of two areas in southwestern Germany, with rich and complex prehistoric occupation and a wide range of archaeological evidence from the Upper Palaeolithic period onwards: The Upper Neckar and Upper Swabia. In the first study area, a palaeo-wetland within the Ammer River Valley in the Upper Neckar was chosen. It corresponds to the overall distribution limit of the Linear Bandkeramik (LBK) with over 200 Neolithic sites, such as Lüsse and Unteres Feld, which were studied archaeologically in detail. Adjacent to the study area (6 km distance) is the well-stratified, open-air Mesolithic site of Rottenburg-Siebenlinden. In the second study area, the Upper Swabian region, the focus was on Olzreuter Lake. It is located in the vicinity of Bad Schussenried, at about 97 km south-east from the Ammer River Valley and ca. 10 km from the archaeologically well-studied UNESCO world heritage sites of Federsee. Archaeological evidence from the lake shores and nearby Olzreuter-Enzisholz pointed to a Late Neolithic and Bronze Age human occupation. Two parallel sediment cores covering the period of the Early Holocene were retrieved from the Ammer River Valley, X039 A (14 m) and X039B (16 m). At the Olzreuter Lake, two parallel sediment cores were retrieved, OZ1 (8 m) and OZ2 (9 m), covering the period from the Late Glacial until the Late Holocene. In these sediment cores, a multi-proxy analysis was applied, aiming to understand the potential effect of climatic variability, changes in the landscape, and land-use strategies. These analyses included pollen and spores, NPPs, charcoal, diatoms, chrysophytes, total organic carbon (TOC), geochemical (micro-XRF), radiocarbon dating and lithological proxies. During the Late Glacial and Early Holocene, besides climate, also fire was the principal driver of environmental changes. However, it is still heavily debated if anthropogenic fire co-shaped the environment already during the Early Holocene or only later on. The results of the current high-resolution multi-proxy study, along with detailed archaeological evidence about settlement dynamics and land use development, allowed us to understand the impact of human agency and climate on vegetation and aquatic ecosystems. In both areas, the Late Glacial/Early Holocene started as a period ruled by open vegetation with a high abundance of Pinus, Betula, Artemisia, and Poaceae. After ameliorating the climate, Corylus started to rise at 10.8 cal ka BP in Ammer River Valley and Olzreuter Lake at 10.65 cal ka BP, indicating the dominance of open woodland in both landscapes. Results of micro- and macrocharcoal records from both Olzreuter Lake and Ammer River Valley show that during the Late Glacial, fire events were determined by climatic variability rather than the effect of human agency, but soon after, at the beginning of the Early Holocene anthropogenic activities can be linked to fire events. Mesolithic people probably applied fire to keep the opening of the landscapes and enhance the spread of advantageous vegetation, e.g., hazelnuts. The palaeofire records from the Early Holocene in the Ammer River Valley indicate wildfires from 11.6-10.6 cal ka BP, which facilitated the persistence of open and pioneer vegetation. Soon after, the domination of a river landscape was replaced by a palaeo-wetland with open shallow waters that were attractive to Mesolithic populations. The Ammer River Valley was then dominated by Corylus (10.1 cal ka BP) but also provided a wide range of other plant resources. From ca. 9.5 cal ka BP, archaeological evidence coincides with the timeframe when frequent, low-intensity fires (e.g., pattern typical for human-induced palaeofire) and vegetation disruption occurred, and therefore, the use of fire by hunter-gatherers shall not be neglected. In this study, soon after the 8.2 rapid climate change event, the rise of the mixed oak forest is noticeable in both regions, with the Corylus pollen decreasing but persisting in the landscapes probably because of the suitable wetland habitats in the surrounding both studied cores. The palaeoecological record at Olzreuter Lake also covers the period after the Early Holocene. The dominance of mixed oak forests ends at circa 6.2 cal ka BP, with the abrupt increase in Fagus. Closed forests arise thanks to the intense domination of Fagus, out-competing the elements of the mixed oak forest by shadowing them. In the Middle Holocene and Late Holocene, settlement activities and fire events show a clear relation. The agricultural practices in the vicinity of Olzreuter Lake during the Late Neolithic and Bronze Age are reflected by vegetation change and specific patterns of the studied charcoal records. Lake productivity had suffered several fluctuations over time, with the appearance and disappearance of diatoms and Chrysophytes. Ecological changes in the lake, small lake level fluctuations, and physicochemical and biological processes can be specially noticed from the Middle Holocene onwards and essentially can be linked with climatic and anthropogenic agency.

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