Late-glacial and Holocene vegetation and climate change at the Palu glacier, Bernina pass, Grisons canton, Switzerland

Pollen and macrofossil data from Alpe Palu, south-eastern Switzerland, are presented. On the basis of these data and the geomorphological evidence for local glacier movement, Holocene climatic oscillations and vegetation change at this upland site (1940 m asl), are reconstructed. The morainic deposits and glacial clays, as well as the pollen data from the base of the pollen profile, clearly show that the Palu glacier, after its retreat from the Cavaglia (Egesen) stade, readvanced once again shortly before the mid-Preboreal. This re-advance was considerably greater than that dating to the Little Ice Age. This early Holocene climatic event is referred to as the Palu Oscillation (Paluw-Schwankung) and is considered to be broadly contemporaneous with the previously described Schlaten Oscillation (Schlatan-Schwankung:) in the Austrian Alps. The reforestation of the forefield of the moraine was interrupted at least twice during this oscillation, and, compared with neighbouring sites at the same altitude, it appears to be at least 500-700 years younger, i. e. it post-dates 9400 B.P. Though the Palu Oscillation is a Holocene phenomenon, the associated vegetation changes are Late-glacial in character, e.g. Artemisia and Chenopodiaceae increase and Hippophae is recorded Alnus viridis replaces Betula and Salix, which were important in the earlier part of the Holocene, at about 5000 B.P. There is no clear evidence that forest burning is attributable to human activity. The use of Larix-dominated areas as pasture (Larchwiesen) begins in the mid-Bronze Age. A strong decline in Picea (spruce) and Larix (larch), and an increase in Poaceae, Plantago and other herbs in the uppermost horizons reflect more intensive pastoral farming that began in the high Middle Ages.