Late-glacial and early-Holocene palaeoenvironments in Brianza, N Italy

Abstract

The Late-Glacial and early-Holocene vegetation development in Brianza is shown by the pollen diagrams from Lago di Annone (226 m a.s.l.) and Lago del Segrino (374 m a.s.l.). both situated just inside the moraine system of the maximum Wurm glaciation. After the retreat of the Adda glacier an open steppe vegetation dominated by Artemisia and Gramineae spread in the area. A period rich in Juniperus and Hippophae is recorded before the expansion of Betula at ca. 13,700 BP, which coincided with sediment changes from silt to calcareous gyttja in the lakes. The open Betula forests developed towards denser Pinus-Betula forests at around 12,350 BP, and Quercus, Ulmus, Tilia, and Alnus started to expand during the Altered. The latter were seriously affected by the climatic deterioration of the Younger Dryas, whereas Juniperus, Betula, Artemisia, and some other herbs indicating steppic conditions became more frequent. The Younger Dryas can be divided into three biozones, most likely representing different climatic conditions. High percentages of NAP throughout the Late-glacial and a very pronounced Younger Dryas with high values of Artemisia, Umbeiliferae, and other indicators for dry climate may suggest that the limiting factor for tree growth was not only temperature but also precipitation. The beginning of the Holocene is marked by decreases in Betula and heliophilous herbs and the expansion of deciduous forests dominated by Quercus, Ulmus, and Tilia.