Esquisse au charbon de bois des paysages d'altitude des Alpes du sud (France)

Abstract

Pedoanthracological analysis is based on the identification and dating of charcoal fragments buried in soil. This method makes it possible to reconstruct with high spatial accuracy the history of burnt ligneous vegetation. When applied to the uppermost belt of the southern inner French Alps, it allows us to reconstitute the landscape history related to human activities. All of the samples (thirty four) derived from the treeless belt between 1950 m and 2919 m provided charcoal fragments. The latter are the testimony to the role of burning episodes in the establishment of present vegetational structures. Anthracological analysis shows that the upper forest belt as a whole was colonized by arolla pine (Pinus cembra L.) and larch (Larix decidua Mill.) : up to 2400 m, forest communities were relatively closed and dominated by the arolla pine. Between 2400 m and 2700 m, plant communities consisted mainly of a Juniperus arid Ericaceae heath, with scattered arolla pines and larches : the treeline reached 2700 m. Results show that the upper forest limit was about 500 m higher than today. Charcoal datings ranging from 5 000 BC to present demonstrate that agro-pastoral activities are responsible for vegetation changes and landscape structures. The present upper forest belt is the consequence of both human activities and climatic conditions.