A LATE-GLACIAL POLLEN RECORD FROM TWIN PONDS, CENTRAL VERMONT

A high-resolution pollen record (50-200 year intervals) from the littoral zone of Twin Ponds, a carbonate-rich lake in central VT, contributes to our understanding of regional vegetation and climate during the late-glacial period (ca. 13,000-9,000 cal yr BP). High percentages (40-73%) of Picea pollen dominate the base of the record until 11,500 cal yr BP. Pollen influx rates suggest that this early Picea period had two stages. The first stage is characterized by low Picea pollen influx rates (400-750 grains/g/yr) and the second by an increase in Picea influx rates (1100-1800 grains/g/yr) and a small increase in Abies pollen percentages at around 12,700 cal yr BP. Following 11,500 cal yr BP, percentages and influx rates of Picea pollen declined. The period from 11,500-10,900 cal yr BP is characterized by peaks in multiple arboreal taxa including Abies, Pinus, Larix, and Betula and by an increase in total spores. Starting at 11,100 cal yr BP, Abies, Pinus, and Larix decline but Betula continues to increase and peaks around 10,900 cal yr BP. After 10,900 cal yr BP, Betula gradually declines and Pinus and Quercus become the dominant taxa.

The pollen record from Twin Ponds indicates rapid vegetation and climate change during the late-glacial period. From 13,000-12,700 cal yr BP, Twin Ponds was dominated by an open Picea woodland and conditions were colder and drier than present. From 12,700 -11,500 cal yr BP the vegetation shifted to a closed boreal forest, which suggests the persistence of colder than present temperatures and an increase in moisture from the previous time period. This time period coincides with the Younger Dryas cooling event. Following 11,500 cal yr BP, the pollen data show a more diverse, closed boreal forest and the expansion of wetlands, both of which imply conditions that were warmer and wetter than previously. The increase in diversity during this period was also influenced by the migration of taxa into the region from the south. After 10,900 cal yr BP, the pollen data suggests a mixed forest dominated by Pinus and Quercus and with increasing amounts of other deciduous taxa such as Acer, Fraxinus, and Ostrya/Carpinus. This represents a shift climatically to the warmest and driest conditions observed in this record and the continued expansion of arboreal taxa into central Vermont.