Holocene Palaeoenvironments at the Timberline in the Taillefer Massif,French Alps: A Study of Pollen,plant Macrofossils and Fossil Insects

Abstract

In order to reconstruct the history of the tree-line fluctuations, an integrated palaeoecological study of pollen, plant macrofossils and insect fossils was made in two peat-bogs containing Pinus uncinata trunks in the Taillefer Massif (Isére, France) at an altitude of 2100 m (i.e., above the present timberline). There is apparently an absence of a local woodland during the Lateglacial. After a hiatus corresponding to the beginning of the Holocene, the local presence of P. uncinata is recorded from at least 7500 BP onwards. There are also indications of Abies woodland in the vicinity of the plateau during the Atlantic chronozone. Significant changes in regional ecosystems are recorded from 5000 BP in an expansion of Fagus and Pinus cembra, and the first pollen evidence for human activities. Plant macrofossils and fossil insects (mainly Coleoptera) significantly improved the interpretations based on pollen analysis. Pinus uncinata disappeared from the plateau at about 2000 BP, slightly before the expansion of Picea at lower altitude. Pollen data imply that the timberline recession may be due to the exploitation of the forest by man. However, a lowering of the snow-line coinciding with the decline of Pinus uncinata is attested by the appearance of the insect Helophorus glacialis. It is therefore probable that there was a combination of human action and climatic impact, the importance of the latter having often been underestimated up to now.