Development and analyses of tree-ring chronologies to reconstruct prehistoric environmental conditions in West and Central Europe

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Tree rings of recent trees, historical timbers, subfossil trees and timbers from archaeological context constitute one of the most important fundament of Paleosciences. No other environmental archive with annual resolution covers the entire Holocene. The signatures of tree-ring widths, stable isotopes and radioisotopes can be used for climate and environmental reconstructions. But they also serve for precise dating of wooden finds and other important archives such as ice cores, speleothems or sediments.Resulting climate reconstructions and precise dendrochronological datings allow archaeologists and historians to better assess the living conditions of people in the past and to question environmental impacts on economy and society. The modern climate change can thus be retrospectively placed in their Holocene context. Therefore, a consistent expansion of tree-ring chronologies over the Holocene until the Late Glacial is of particular importance. The conditions are ideal in Europe. Worldwide, the "South German tree-ring chronology" of the University of Hohenheim spanning the last 12,460 years (Becker et al. 1982, Friedrich et al. 2004) is unique, although the data were never published in full.Achievements during my current project funded by the German Science Foundation (SP 437/16-1, 1.2.2015 – 31.1.2018) were to develop high replicated Central European oak tree-ring chronologies to close gaps, and to use them as a basis for hydro-climatic reconstructions. Unexpectedly, we have succeeded in compiling a previously unpublished database of oak tree-ring width series from 14 European dendro-archaeological laboratories in a single database. This is a worldwide unique new dataset comprising a total of 63.730 tree-ring width measurements from 4.815 sites covering the last 7.500 years. So far, a careful processing, harmonization and quality control was performed. However, a comprehensive analysis of this extensive dataset could not be accomplished in the current and now ending project. Therefore, an extension of the project by two years for the analysis and hydro-climate reconstructions is needed. Ongoing experiments revealed surprisingly close relationships between tree-ring width and groundwater fluctuations. This is new knowledge, and it would be desirable to continue the analyses with the aim to reconstruct historical groundwater fluctuations over the last 7.500 years. The project extension by two years is therefore justified and highly promising results are expected.