Detecting prehistoric fire-based farming using biogeochemical markers

The Holocene fire history of Central Europe has revealed that the charred organic matter found in soils today results basically from anthropogenic burning. The vegetation fires laid since the Early Holocene may well have influenced the properties of soils; the early human impact on the global climate system could also be connected to this prehistoric burning. The present thesis contributes to the investigation of potential effects of prehistoric anthropogenic burning on soils. Information about prehistorical agricultural techniques such as slash-and-burn and their impact on the environment are scarce. We do not know much about the processes that consequently lead to the change of natural environments into human-dominated, open cultural landscapes, as it is indicated by several terrestrial archives and proxy-records from the Neolithic (5500-2200 BC). Advantage was taken of an experimental burning in Forchtenberg (SW-Germany), to determine how much charcoal is produced by slash-and-burn in temperate deciduous forests and if fire affected soil carbon budgets and soil lightness. The charcoal produced by slash-and-burn was slowly incorporated into the soil profile, this was mainly done by earthworms. The aromatic compounds in charcoals are correlated to soil colour, they could be responsible for the dark colour of Chernozems and related soil types. It is not known how much charcoal has been transferred into soils since prehistoric fire-use started, and how high the charcoal loss has been, e.g. by decomposition or erosion. However, after even one fire the mass of potentially available charcoal is relatively high. A literature review was made to elucidate which are the main soil forming factors controlling the pedogenesis of Central European Chernozems. The distribution of Chernozems does not seem to be dependent on natural factors alone, not all the soils possessing Chernozem properties can be steppe soils. Biomass burning, including that for agriculture, might be an important formation factor. It is now an open question as to wether Neolithic settlers did indeed prefer to grow crops where Chernozems occurred or if Neolithic burning formed the chernozemic soils. Biogeochemical markers were used to investigate if Luvic Phaeozems in the Lower Rhine Basin are the natural successors of Early Holocene Chernozems. It was concluded that the investigated dark soils formed as a result of anthropogenic burning during several (pre)historic epochs. A general use of other soil amendments like manure could not be proven. The investigated soils should not be classified as Luvic Phaeozems, they are Luvisols containing a degraded (fossil) anthric horizon. The occurrence of these dark soil horizons documented the transition from a natural to a human-dominated landscape. Additionally, soil charcoals from Southern Switzerland were investigated to obtain further information concerning fire and vegetation history. It was found that the chestnut was present in Southern Switzerland about 1000 years earlier than predicted by the pollen based model of the introduction of the chestnut (Castanea sativa) by the Romans. The application of geochemical methods to detect human impact on soils was problematic for phosphorus and lipid analysis, mainly because not enough control samples were available. Soil charcoal analyses, including 14C dating of microcharcoal, are considered useful tools forreconstructing palaeoenvironments. A main future task would be to consolidate the existing archaeological and palaeoecological data to build an extended model of human impact on the environment in prehistoric societies.