Palynological investigations reveal Eemian interglacial vegetation dynamics at Spiezberg, Bernese Alps, Switzerland

Abstract

Interglacial pollen records are valuable archives of past vegetation dynamics and provide important information about vegetation responses to different-than-today climates. Interglacial pollen archives pre-dating the Last Glacial Maximum (LGM) are scarce on the Swiss Plateau in contrast to the many available Late Glacial and Holocene records. This is mainly due to the rapidly changing palaeo-environmental conditions throughout the Quaternary and the low preservation potential of material suitable for palynological investigations. The Spiezberg site offers a palynological record situated most proximal to the Alps in Switzerland. Previous investigations tentatively assigned this record to the Eemian interglacial (MIS 5e). We have conducted additional pollen analytical investigations to increase the quantity of pollen information. Besides biostratigraphic interpretations, we use numerical methods such as distance analysis (distantia) and ordination techniques (PCA) to evaluate the similarities and differences between the Spiezberg record and its geographically and chronostratigraphically closest physically dated (U/Th, luminescence) analogues from the Eemian (MIS 5e) and Meikirch 3 (MIS 7a) interglacials. Our palynological investigations reveal the predominance of closed temperate forests with abundant fir (Abies) and spruce (Picea) as well as evergreen broad-leaved taxa (e.g. Hedera). The attribution to the Eemian interglacial relies on the observation of very rare beech (Fagus) occurrences, a phase with prominent yew (Taxus) and the unimportance of hornbeam (Carpinus), all of which are typical Eemian features on the Swiss Plateau. An Eemian age is supported by the numerical comparison with the Beerenmösli (MIS 5e) and Meikirch 3 (MIS 7a) reference records. Furthermore, the Picea, Taxus and Fagus dynamics observed on the Swiss Plateau during the Eemian are in excellent agreement with vegetational patterns observed elsewhere in Central Europe. Surprisingly, Carpinus was almost absent on the Swiss Plateau during the Eemian, whereas it was a major component of the forest at other European sites with a similar elevation as Spiezberg. We explain this by environmental conditions and the strong competition with Abies alba. In particular, considering the European Eemian vegetation history and the results of our reconstructions from the Swiss Plateau, we find that Abies alba was a highly competitive tree under natural warmer-than-today conditions. This finding provides further evidence that Abies alba may benefit from future climate warming.