Elevation-induced variations of pollen assemblages in the North-western Alps: An analysis of their value as temperature indicators.

Seventy-seven modern pollen samples from various elevations (350-2680 m a.s.l.) in two different areas of the north-western Alps (the Aosta Valley, Italy and the Taillefer Massif, France) were statistically analyzed to derive correlations between pollen assemblages, elevation and temperature at the sampled points. Numerical classifications were performed on pollen data to judge similarities between the two areas. The results show that a strong relationship exists between altitude and variations in pollen taxa percentages despite some floristic differences between the two areas. As a test, transfer functions from pollen percentages to elevation and temperature were calculated from pollen data. The reconstruction appears to be reliable, with a higher reliability at sites located over 1000m. This analysis aims to serve as a basis for further quantitative reconstruction of temperature changes during the Holocene based on fossil pollen data from sensitive regions that encompass a significant altitudinal gradient.

[Role of man in the history of vegetation of the Ellero valley (maritime Alps, Italy)]. / Rôle de l'homme dans l'histoire de la végétation de la vallée Ellero (Alpes maritimes, Italie).

The pollen analysis of a sediment core from a peat bog (Rifugio Mondovi) at the mountain belt (1760 m) in the Ellero Valley (Italian Maritime Alps) shows the postglacial vegetation history. The sequence starts at 12,000 BP during a peak of pine pollen; this first phase shows a low representation of birch and the presence of Tilia. Younger Dryas is characterised by increasing percentages of Artemisia, showing the presence of deciduous Quercus, fir and beech. Elm appears at the beginning of the Holocene during the second pine peak (9800 BP). A 3000-year hiatus is present. Sedimentation resumes at 6000 BP in a Rhododendron fir-wood. The present timberline at 1500 m, at the limit of the beech wood, is a result of the decline of the fir-wood at 2600 BP, which allowed an expansion of beech. During this period, there was a continual increase in Gramineae and deciduous oak and the first occurrences of evergreen oak are observed. The development of larch occurs at 1800 BP, together with walnut, chestnut, cereals and vine.