Glacial/postglacial transition south of Splugen Pass: environment and human activity

Abstract

Starting in 1986, exploration and survey on the Italian side of the Spiugen Pass watershed have resulted in the discovery of 38 prehistoric sites at elevations of 2000-2420 m in the inner Central Alps. Out of 25 Mesolithic sites, two on the Pian dei Cavaili Plateau have been excavated. In agreement with artifactual records, 14C dates cluster at c.8200-7900 (Early Mesolithic, local phase 1) and c.6800-6350 cal BC (Mesolithic phase 2). Man-made fires in the 8500-7850 and c.7300-6300 cal BC intervals are indicated by charcoal particles at the nearby Lago Basso. A major group of Early Mesolithic sites lies along the plateau northern escarpment (2200-2260 m a.s.I.), deglaciated since B0lling-Aller0d times. Chert and quartz raw materials reveal circulation across elevated terrain, possibly including the Alpine watershed itself. The Late Glacial and Early Holocene vegetation development on Pian dei Cavaili is shown by a combined pollen- and macrofossil diagram from Lago Basso (2250 m), tied to a 14C timescale. Late Glacial treeless pioneer vegetation developed towards closed meadows during the early Preboreal, while the first sparse trees of Pinus cembra and Betuia arrived near the lake. Following an increase in dwarf shrubs, mainly Juniperus, a mass expansion of Larix occurred at ca.7700 cal BC, and Picea abies started to expand in the subalpine Larix-Pinus forest around 7000 cal BC. The Mesolithic phases 1 and 2 coincide with periods of rather open vegetation on Pian dei Cavaili, the phase 1 landscape on the northern escarpment being a timberline ecotone. Phase 2 is coeval with the end of the Venediger oscillation; a delay in reforestation after this period of climatic tim-berline depression, coupled with high charcoal values at Lago Basso, suggests that Mesolithic hunters kept the surroundings open by burning young trees.