Origins of European biodiversity: palaeo-geographic signification of peat inception during the Holocene in the granitic eastern Massif Central (France)
Résumé
Mires are rare, unique environments that greatly contribute to biodiversity and occupy key functions in the hydrological cycle, but today many of these ecosystems are menaced, making conservation measures necessary. The efficiency of these measures is partly related to our knowledge of their origins and their development, a question rarely addressed. In this paper we examine the development of mires during the 10.000 last years (Holocene) in the eastern Massif Central, France, focusing on the contributions of climate change and human activities. Radiocarbon dates of the basal layers of 63 sites show that many mires formed around 7500 BP. During the Holocene, many mires were formed in the Atlantic period, characterised by warmer and wetter climatic conditions. At shorter time scales of 103–102 years, several other factors are related to peat inception, including topography, geomorphology and superficial geology, vegetation successions and human-induced changes. There is evidence that the building of small dams in headwater streams during the Iron age induced local water logging which then lead to the initiation and growth of mires. The influence of Bronze age communities is further demonstrated by new pollen analysis results. Forest clearing and grazing also favoured soil water logging, enabling peat inception. We consider human societies to be responsible for the formation of some mires. Human activities can be considered to having taken part in the development of the European biodiversity at least during the last 5 millennium.