Exploring the ancient occupation of a high altitude site (Lake Lauzon, France) : Comparison between pollen and non-pollen palynomorphs

International audienceNext to Lus-la-Croix-Haute (Southern Alps, Drome, France), Lake Lauzon is located in a small basin 1980[no-break space]m above sea level, 500[no-break space]m above the actual timberline, in the middle of typical sub-alpine grasslands. A drilling for samples in the wetland area bordering the lake made it possible to obtain a core of clayey fine sediments with a high organic matter content, in which pollen as well as many micro-organisms had been particularly well preserved. The pollen analysis and the non-pollen palynomorhs analysis both cover a period from ca. 8000[no-break space]cal. BP to sub-recent time. The pollen analysis reveals the presence of a thriving forest vegetation dominated by Abies, and the first signs of human activity near the lake and its nearby basins in the Atlantic period. These signs become more pronounced during the Sub-boreal period from 5450[no-break space]cal. BP on, with the clear presence of cereal and weed pollen. This evolution is totally confirmed by the non-pollen palynomorphs. Since the Neolithic, every time pollen analysis points to clearings or cultivation, the non-pollen palynomorphs indicate that man has burnt the vegetation to obtain openings (occurrence of Chaetomium sp.). Increased erosion during the Sub-atlantic period is revealed by the occurrence of Glomus cf. fasciculatum. Furthermore, non-pollen palynomorphs give information on eutrophication of the lake which may be explained by more nutrient-rich habitats around the lake due to grazing and possibly agriculture. The combination of both types of analysis makes it possible to prove that this elevated site has been occupied and cleared at an early stage by man to obtain pasture lands and possibly arable land. This led to deforestation, which increased during the Sub-atlantic period, and has led to the present grasslands