VEGETATION CHANGE AND ENVIRONMENTAL SUCCESSION IN CENTRAL NEW YORK AFTER THE VALLEY HEADS DEGLACIATION: THE LATE PLEISTOCENE-MID HOLOCENE MACROFOSSIL AND SEDIMENTOLOGICAL RECORDS OF PURVIS ROAD BOG

Long-term climate change since the Late Glacial Period has had a profound impact on the vegetation types found in central New York, but paleoenvironmental data on long-term, species-specific vegetation change on a localized scale during the post-glacial period has been poor. Plant macrofossils preserved in the sediments of the region’s numerous lakes and wetlands offer a valuable paleoenvironmental record for filling this void. We report here on our investigation of the macrofossil and sedimentological records at Purvis Road Bog, an ombrotrophic peat bog in central New York. The bog is located at the southernmost boundary of the Late Pleistocene Valley Heads glaciation; the bog's kettle basin formed during the ice sheet’s retreat. We sampled macrofossils from three 1-m sediment cores obtained from basal depths and a 7-m radiocarbon dated core, concentrating on material from the Late Pleistocene to mid-Holocene (ca. 12.76k-4k yr BP). Macroscopic charcoal and loss on ignition analyses were also employed.

Sediment cores from Purvis contain six identified lithological zones, which record an overall rise in sediment organic content as infilling transformed the site from a kettle pond to the present-day raised peat bog environment. The earliest zone sampled on our cores is a lacustrine clay, whose pre-12.76k yr BP date is considered significant constraining date for understanding the timing of the Valley Heads deglaciation. Vegetation from this period is largely comprised of boreal tree species and sedges that grew around the kettle pond. Wetland and boreal forest taxa become more common in the next two lithological zones, which include a record of the Younger Dryas cooling event (ca. 10.85k-10.2k yr BP). Fire activity, inferred from a rise in charcoal, appears to have increased during this period, and a charcoal influx peak in 10.2k yr BP signals fire events that may have led to higher erosion rates responsible for an intrusive sand layer in the pond basin. A gradual rise in temperature and moisture marks the remainder of the early Holocene record (10.2k-5.9k yr BP), when temperate forest taxa become common, and increases in sediment organic content and sphagnum macrofossils indicate basin infilling, such that by the mid-Holocene (4k yr BP), the bog’s present-day vegetation dominates the macrofossil record.