Regional vegetation-cover changes on the Swiss Plateau during the past two millennia: A pollen-based reconstruction using the REVEALS model

We aim to quantify the changes in regional vegetation cover on the Swiss Plateau during the past two millennia with the recently developed REVEALS model. We used pollen data from four large lakes (≥520 ha), namely (1) Baldeggersee, Hallwilersee, and Greifensee on the Swiss Plateau and from (2) Zugersee at the Swiss Plateau-Alps transition. Also, we used pollen productivity estimates (PPEs) that are available for 13 taxa in this region. First, we estimated present-day vegetation and land-cover composition on the Swiss Plateau. The REVEALS result is much more similar to the observed composition than the pollen percentages from modern surface sediment samples, thus confirming the robustness of the REVEALS approach for the Swiss Plateau. We then reconstructed regional vegetation composition in 200-year intervals over the past two millennia. In both investigated regions the REVEALS results showed a strong anthropogenic impact on vegetation: the results suggest that the landscape was much more open (20-80%) throughout the past 2000 years than pollen percentages (10-50%) suggest. Our model results provide quantitative and more realistic estimates of the regional vegetation and land-cover changes that are relevant for assessing regional vegetation-climate feedbacks. However, PPEs for more plant taxa as well as further assessment of PPEs, particularly for Cerealia, are needed. Also, the model-inferred quantitative vegetation changes reflect the regional differences in agricultural and other human activities during the Roman Time, the Migration Period, the early and late Middle Ages, and since the onset of Modern Times.