Vegetational response to climatic changes recorded in Swiss Late Glacial lake sediments

High-resolution pollen analysis at five lakes on an altitudinal transect in Switzerland (Gerzensee, 603 m; Leysin, 1230 m; Regenmoos, 1260 m; Zeneggen, 1510 m; Hérémence, 2290 m) focused on the vegetational response to the rapid climatic changes at the end and beginning of the Younger Dryas and to the minor Gerzensee and Preboreal climatic oscillations. An absolute time scale transferred from the Greenland GRIP ice core to the Gerzensee and Leysin records by wiggle-matching the oxygen-isotope stratigraphies facilitates the estimation of pollen influx and rates of change. The climatic warming at the end of the Younger Dryas, indicated by increases in oxygen-isotope values and/or the beginning of organic sedimentation in the lakes, was immediately reflected in the vegetation at all the sites investigated. The time lags at sites situated above the timberline during the Younger Dryas are considered to be migrational lags. At the onset of the Younger Dryas a time lag of several decades occurred between the oxygen-isotope record of climatic cooling and the major response of the vegetation, whereas minor vegetation changes occurred with or without short time lags. Betula reacted earlier to the new environmental conditions (within about 40–50 yr at Gerzensee and within less than 36 yr at Leysin) than Pinus and Artemisia (about 170 yr), suggesting that time lags are due to the ecological requirements of the different taxa. For the Gerzensee and Preboreal oscillations little or no change can be observed in the pollen record from Gerzensee, whereas at Leysin both climatic oscillations produced a statistically significant vegetational response to both climatic oscillations. Generally the vegetation responses to climatic changes are more pronounced near vegetation ecotones at medium and higher altitudes than in the lowlands.