A twofold development and demise of pine stands in the Netherlands during the Allerød interstadial: two hypotheses to explain a link to climate change recorded in Greenland ice

The second half of the Allerød interstadial in the Netherlands is characterised by pine forest. Excavated trunks of 165 pine trees at Leusden-Den Treek in the central Netherlands (LETR16) were dated by dendrochronology and radiocarbon. Two chronologically separated pine forest phases occurred during relatively warm periods as recorded in Greenland ice. We developed two hypotheses to explain waxing and waning of the two pine phases, with a gap width of more than 300 years, in relation to the climate fluctuations recorded in Greenland. In both hypotheses, climate change triggered the start and demise of pine forest. In the first hypothesis (1), we link the two pine phases with northward migration and retreats during the Allerød interstadial. Trees generally expanded northwards during warm periods from refugia in South and Central Europe, towards Northwest Europe, and died off on a massive scale during the beginning of cold periods. In an alternative hypothesis (2), the presence and absence of pine are explained as the effects of local changes of the groundwater table and related preservation of pine wood, also triggered by the climate fluctuations as recorded in Greenland ice. The two hypotheses are discussed using palynological and lithological data from four studied sample series at the site (LETR16) where pine trees were found, compared to more downwind sites (LESN18 & LEN226). Based on the lithological and palynological data, it is concluded that particularly changes in groundwater level led to the local disappearance of pine but, on the other hand, resulted in preservation of the pine tree remains.