In the Netherlands, several proxies of climate change during the Last Glacial-Interglacial Transition (LGIT) (c. 14,700 to 11,700 b2k) have been investigated in detail over the last few decades. The present paper presents two tree-ring chronologies LETR-A (n = 16, timespan 106 rings) and LETR-B (n = 24, timespan 201 rings) from in situ subfossil pine remains (Pinus sylvestris) discovered at Leusden-Den Treek in the Netherlands that date from the Bølling-Allerød interstadial (GI-1). Using a multiproxy approach (both abiotic and biotic), it was possible to study local woodland development in detail as part of long-term environmental change. Moreover, the trees opened up possibilities for dendrochronological and dendroclimatological research. The tree-ring series show the occurrence of two successive phases of pine woodland development, which were 14 C dated with high precision and calibrated using the recent IntCal20 14 C calibration curve: 13,450–13,396 to 13,370–13,316 calBP (series LETR-A) and 12,952–12,937 to 12,754–12,739 calBP (series LETR-B). At the north-western boundary of its ecotone, Pinus was highly sensitive to climate change during the latter part of GI-1 and the transition to GS-1. The inability to set fruit and the disappearance of the pine woodland within decades before and after c. 12,745 calBP is interpreted as the vegetational response to abrupt climate deterioration at the start of the Younger Dryas (12,807 ± 12 cal BP).