Reconstruction of Holocene high-altitude vegetation cover in the French southern Alps: evidence from soil charcoal

Abstract

The study presented here from the southern French Alps demonstrates the reliability of soil charcoal analysis for the study of Holocene past treeline positions. The occurrence of charcoal in mineral soils along transects from 1950 m up to 2920 m demonstrates the role of fire in the establishment of the present vegetation patterns. The abrupt decrease of charcoal concentration at about 2400—2600 m (which varies across the study sites) corresponds to the modern transition between subalpine forest and alpine tundra. Charcoal particles formed in situ provide high spatial-resolution data for the reconstruction of past forest and treeline changes. Soil charcoal analysis indicated that: (1) treeline was 300 m higher around 6800 cal. BP than today; and (2) the uppermost forest belt up to 2810 m was colonized by larch ( Larix decidua Mill.) and arolla pine ( Pinus cembra L.). This pine is present today but patchily distributed: it is absent from the three areas studied. Radiocarbon dates, ranging from c. 6800 cal. BP to the modern period, along with historical and archaeological data, suggest that the present pattern of the uppermost forest belt, and the patchy distribution of arolla pine in the studied area are the results of anthropogenic fire (mainly agropastoral activities). The question of global warming consequences on treelines in this part of the French Alps is discussed.

Tracking Holocene glacial and high-altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments (Lake Blanc Huez, Western French Alps)

“…Pollens recorded in high-altitude sites usually come from lower altitudes ones after being lifted by vertical air-mass movements (Talon, 2010) and are thus only providing a very general and regional picture of the vegetation cover in surroundings mountainous environments. On the contrary, LCF (figure 7G) quantified throughout the lacustrine sediment in LBH06 are similar to the ones described in the present-day soils samples S1 and S2 from the LBH watershed and soil sample S3 taken nearby under a typical high altitude dwarf shrubby vegetation ( figure 1C).…”

Les dynamiques de la végétation et des anthroposystèmes d’altitude cernées par l’anthracologie pastorale et minière à l’échelle d’un haut vallon alpestre (Freissinières, France)

“…10a). Si on s'appuie sur les données pédoanthracologiques sud-alpines, la limite supérieure des arbres était quant à elle probablement bien plus élevée ; elle pouvait atteindre au milieu de l'Holocène 2 400 à 2 600 m d'altitude voire plus Talon et al, 1998 ;Talon, 2010). L'émergence puis la hausse de la courbe du mélèze dans le diagramme palynologique de Fangeas indique que ce manteau n'était pas totalement continu.…”

Pyrenean ptarmigans decline under climatic and human influences through the Holocene

“…during this period (Cunill et al, 2012(Cunill et al, , 2013. This seems to be a generalized phenomenon in Southern Europe because the tree line also reached its highest level in the Alps at the same period (Ali et al, 2005;Talon, 2010). The high elevation of the tree line during this period likely resulted in a loss and fragmentation of habitat for the rock ptarmigan.…”