Early expansion of mixed oak stands at 16,800–16,600 cal bp at a northern Italian glacial refugium in the Euganean Hills

Continuous sedimentary lake records covering the Last Glacial Maximum (LGM) are very rare in Europe. Here, we conducted additional palynological analyses to connect two separate radiocarbon-dated pollen sequences of Lago della Costa (AP2 and AP1) to one complete vegetation history record of the Euganean Hills (“Colli Euganei”, northern Italy) covering the past ca. 32,000 years. Previous studies on autochthonous organic lake sediments revealed that during the Last Glacial Maximum (LGM) Lago della Costa likely acted as a refugium of temperate woody taxa. Based on the new data we present the first continuous record of the vegetation history of the Euganean Hills during the past 32,000 years. Specifically, we investigate the early establishment and mass expansion of deciduous Quercus at the refugial site at ca. 16,800–16,600 cal BP. In the oak forests other temperate taxa (e.g. Corylus avellana, Abies alba, Ulmus, Fraxinus excelsior, Vitis, Hedera, Tilia, Acer, Fagus sylvatica) also established at around this time, i.e. 2,000 years prior to the onset of the Bølling/Allerød interstadial (about 14,700–12,800 cal BP). The comparison of our data with other well-dated records from the river Po catchment and refugial sites elsewhere in Italy and southern Europe suggests expansions of boreal and nemoral forests over wide areas prior to the Bølling/Allerød interstadial, i.e. 2,000 years before comparable large-scale afforestation north of the Alps or ca. 45°N. Pollen-inferred expansions of temperate tree communities (e.g. oak forests) correspond to a climatic warming as reconstructed from quantitative, pollen-independent evidence (e.g. chironomids) from the Apennines, Northern Italy, Southern Switzerland and the Swiss Plateau, suggesting that pre-Bølling afforestation processes south of the Alps were promoted by increasing (summer) temperatures during the Oldest Dryas.