Mire initiation, climatic change and agricultural expansion over the course of the Late-Holocene in the Massif Central mountain range (France): Causal links and implications for mire conservation

Peat initiation during the Late-Holocene was studied in the eastern part of the Massif Central in France from the analysis of numerous conventional and AMS radiocarbon dates obtained in the basal layers of 83 mires, representative of old, thick deposits, but also of younger and marginal mire areas. Radiocarbon dates were calibrated to calendar years BP in order to generate probability distributions of calibrated radiocarbon dates. Only the oldest dates from each mire were used for this statistical analysis. It appears that the Late-Holocene was one of the two most intensive periods of peat initiation since the end of the glacial period. Peat initiation began around 4500 cal. BP, following a complete halt in the formation of mires from 5300 to 4500 cal. BP. By contrast, peat initiation increased significantly since 2400 cal. BP. This history of Late-Holocene peat initiation is not in agreement with chronologies of climatic change in Western Europe. The hypothesis is that peat initiation during the last 4500 years was a consequence of agricultural expansion in the Massif Central in France, which is supported by pollen and archaeological data. Nevertheless, the possible role of climate in certain periods, for example during the Little Ice Age, is not discounted. In term of conservation, the demonstration of a human origin of certain mires leads to a new interest in these ecosystems, and provide a huge argument in order to protect them. Indeed, because of their existence, they testify to the history of agricultural expansion, and some mires are therefore the object of archaeological studies. (C) 2011 Elsevier Ltd and INQUA.