VEGETATION CHANGES AND TIMBERLINE FLUCTUATIONS IN THE CENTRAL AIRS ASINDICATORS OF HOLOCENE CLIMATIC OSCILLATIONS

Pollen and plant-macrofossil data are presented for two lakes near the timberline in the Italian (Lago Basso, 2250 m) and Swiss Central Alps (Gouille Rion, 2343 m). The reforestation at both sites started at 97 00-9500 BP with Pinus cembra, Larix decidua, and Betula. The timberlin e reached its highest elevation between 8700 and 5000 BP and retreated after 5000 BP, due to a mid-Holocene climatic change and increasing h uman impact since about 3500 BP (Bronze Age). The expansion of Picea a bies at Lago Basso between ca. 7500 and 6200 BP was probably favored b y cold phases accompanied by increased oceanicity, whereas in the area of Gouille Pion, where spruce expanded rather late (between 4500 and 3500 BP), human influence equally might have been important. The mass expansion of Alnus Viridis between ca. 5000 and 3500 BP probably can b e related to bath climatic change and human activity at timberline. Du ring the early and middle Holocene a series of timberline fluctuations is recorded as declines in pollen and macrofossil concentrations of t he major tree species, and as increases in nonarboreal pollen in the p ollen percentage diagram of Gouille Rion. Most of the periods of low t imberline can be correlated by radiocarbon dating with climatic change s in the Alps as indicated by glacier advances in combination with pal ynological records, solifluction, and dendroclimatical data. Lago Bass o and Gouille Rion are the only sites in the Alps showing complete pal aeobotanical records of cold phases between 10,000 and 2000 BP with ve ry good time control. The altitudinal range of the Holocene treeline f luctuations caused by climate most likely was not more than 100 to 150 m. A possible correlation of a cold period at ca. 7500-6500 BP (Miser oscillation) in the Alps is made with paleoecological data from North America and Scandinavia and a climatic signal in the GRIP ice core fr om central Greenland 8200 yr ago (ca. 7400 yr uncal. BP).