LATE-GLACIAL PINE EXPANSION IN THE NORTHERN FRENCH ALPS

A pollen-analytical study, associated with a search of plant macroscopic remains, at eight lakes or peat-bogs in the northern Alps, reveals the role of altitude in the distribution of the main arboreal taxa during the Lateglacial. In the Belledonne massif, during the Lateglacial Interstadial optimum (Allerod), plant macroscopic remains indicate the presence of Pinus up to 1,000 m altitude and that of Betula at the upper tree-limit (1,330 m). This limit was at 1,730 m in the Beaufortin massif. The Younger Dryas was marked by the disappearance of Betula above 700 m at least on two occasions and by the persistence of Pinus at the upper tree-limit (1,000 m). These results led us to reexamine the notion of ''high-altitude pine forests '', and to develop a methodological approach suitable for the reconstruction of the upper tree-limit.