Dissertations, Theses, and Capstone Projects

Date of Degree

9-2016

Document Type

Dissertation

Degree Name

Ph.D.

Program

Earth & Environmental Sciences

Advisor

Rebecca A. Boger

Committee Members

Dorothy M. Peteet

Arthur Bankoff

Yuri Gorokhovich

Ksenija Borojevic

Subject Categories

Climate | Earth Sciences | Environmental Indicators and Impact Assessment | Paleobiology | Paleontology | Sedimentology

Keywords

The Common Era, The Little Ice Age, Paleoclimate, Paleoecology, Paleoenvironment, Human-environmental interactions, The Balkans, Serbia, Southeastern Europe

Abstract

The primary objective of this doctoral dissertation is to reconstruct the environmental history of the Central Balkans (Serbia) over the past millennium utilizing biological proxies (pollen, spores, and charcoal), geochemical signals through X-ray fluorescence (XRF), statistical analyses, and atomic mass spectrometry (AMS) 14C chronology. This dissertation establishes the first chronological framework for vegetation-landscape changes in Serbia and discusses the role of humans and climate as underlying processes.

Chapter 1 discusses the background and the nature of the research problem followed by the extensive literature review on the topic of the Holocene climate and paleoecology. The state of Holocene paleoecology in Europe and in the Balkan region are discussed with an emphasis on the last millennium. The Chapter also includes a summary of key socio-ecological studies across Europe and the techniques used to reveal the long-term human-environmental interactions across the Holocene and the Common Era (past 2000 years). The chapter concludes with the significance of the current study.

Chapter 2 presents the first, well-dated, high-resolution record of vegetation and landscape change from Serbia over the past 500 years. Biological proxies (pollen, spores, and charcoal), geochemical analysis through XRF, and a detailed chronology based on AMS 14C dating from a western Serbian sinkhole core suggest complex woodland-grassland dynamics and strong erosional signals throughout the Little Ice Age (LIA; c.1500-1850 CE). An open landscape with prominent steppe vegetation (e.g. Poaceae, Chenopodiaceae) and minor woodland exists during 1540-1720 CE (early LIA), while the late LIA (1720-1850 CE) in this record shows higher tree percentages possibly due to increased moisture availability. The post-LIA Era (1850-2012 CE) brings a disturbed type of vegetation with the presence of weedy genera and an increase in regional woodland. Anthropogenic indicators for agricultural, pastoral and fire practices in the region together attest to the dominant role of humans in shaping this Balkan landscape throughout the interval. The changing nature of human interference, potentially as a response to underlying climatic transitions, is evident through large-scale soil depletion resulting from grazing and land clearance during the early LIA and stabilization of arable lands during the late and post-LIA eras.

Chapter 3 describes a well-dated, high-resolution Central Balkan record of vegetation and landscape change over the past 700 years from the Sava Region, Serbia. This timespan includes the LIA (1500-1850 CE) with several centuries before and after this important interval for comparison. Biological proxies (pollen, spores, and charcoal), geochemical analysis through X-ray Fluorescence (XRF), and a detailed chronology based on AMS 14C dating from the Sava basin sediments delimit the evolution of the Serbian landscape across a warm-stable pre-LIA interval with relatively high tree percentages, modest occurrence of anthropogenic taxa, and relatively stable agriculture supported by grazing. On the contrary, the LIA interval in the region is expressed through opening and closing of the tree canopies and extensive land erosion, perhaps in response to climatic deterioration and human impact largely associated with socio-political changes of the time. The post-LIA interval shows stabilized woodland in the riparian region, establishment of arable lands nearby lakes and selective forest clearance strategies by humans in the wake of the industrial revolution. Establishing correlation with existing Serbian environmental datasets, this record reveals the transformation of the Central Balkan landscape and its apparent linkages with changing climatic and socio-political regimes.

Chapter 3 also includes a regional comparison between the Sava core and western Serbian lake to capture the nature and impact of the LIA climatic condition and contemporary human societies on the Central Balkan landscapes. During the 15th-19th CE, indigenous tree (e.g. Quercus, Acer, Pinus) and herbaceous (e.g. Poaceae, Chenopodiaceae, Artemisia) pollen from these records demonstrate fluctuations in woodland-grassland dynamics. While tree populations from the Sava region slowly fluctuate between 50 and 70%, the trees of western Serbia vacillate drastically between 30% and 55%. On the other hand, the Sava region grasslands show variations of ~20-43% whereas the western Serbian grass populations exhibit abrupt oscillations between high (59%) and low (32%) percentages. As a proxy for surface erosion and clastic input into the lakes, the 1-cm resolution potassium and titanium counts are in strong agreement with varying herbaceous taxa. While temporal asynchroneity in the AP and NAP signals between the two cores could be attributed to local factors including differing altitude, terrain exposure, and soils that are inherently different on either sides of the Sava channel, continuous oscillations of both communities during the LIA are analogous. This overall pattern indicates that the Central Balkan landscape at-large was going through considerable environmental change throughout the LIA in the form of opening and closing of the tree canopies on both sides of the Sava Basin. High charcoal indicates accelerated land clearance between the 15th and 17th CE, however, towards the beginning of 18th CE, the cultivars (e.g. Secale, Triticum) peak to suggest improved agriculture in the region. Correlation with the available Serbian environmental records across the LIA reveals the regional dynamics between woodland and grassland under the influence of an unstable and perhaps drier LIA climatic regime (especially in the early LIA) and reforestation of the region during the latter part of the LIA due to both climatic and socio-political reasons. This correlation enhances our understanding of the nature and spatial variability of the LIA across the Balkans and its interactions with the contemporary societies.

Chapter 4 examines the interactions of environmental and social dynamics in Central Balkans over the past 700 years, a period that experienced the LIA climatic condition and the warm 20th century. Meanwhile, the same period witnessed a complex human history with the emergence-rise-decline of the Ottoman Empire and subsequent socio-political events (e.g. wars, famines, migrations, epidemics). Environmental datasets for this socio-environmental analysis include biological proxies (pollen, spores, and charcoal), geochemical signals, and a detailed AMS 14C based chronology of two Central Balkan lakes while social datasets include historic population data, land use, records of societal calamities, and critical historic events derived from a review of the literature and local archives. Among the environmental datasets, indigenous tree and herbaceous pollen from the Central Balkans demonstrate fluctuations in woodland-grassland dynamics whereas potassium counts obtained through XRF act as a proxy for surface erosion and clastic input into the lakes. Microscopic charcoal, cereal pollen and subordinate anthropogenic pollen (e.g. cultivated fruits and vegetables) are used to distinguish the nature of human impact over the landscape. These key anthropogenic indicators create a more thorough social component of the analysis in association with other social datasets. After reconstructing the individual time series for each environmental and social dataset and their synthesis using Principal Component Analysis (PCA), the two Central Balkan records are correlated in order to visualize how a region responds to social and environmental stressors. Our approach demonstrates ways to integrate natural and social science systems research.

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