DENDROCLIMATOLOGY OF WHITE OAK TREES IN THE SHENANDOAH VALLEY, VIRGINIA

Stable carbon isotopes (δ¹³C) are now widely used as a proxy in dendroclimatology. During a tree’s life span, climatic factors such as temperature, rainfall, and humidity modulate the rate of photosynthesis. A tree’s response to these external conditions are therefore recorded in the δ¹³C value of wood tissue. In this study, we sought to calibrate local climate-δ¹³C relationships of white oak trees, Quercus alba, from the Edith J. Carrier Arboretum of James Madison University in Harrisonburg, Virginia. Tree cores were collected with an increment borer in February of 2019 from two mature Q. alba trees growing in well-drained soils on a hillslope. The cores were oven-dried overnight, mounted on wooden blocks, and then polished. Annual rings were identified based on the presence of large vessels in earlywood and more densely packed pores in latewood. We focused solely on latewood to avoid δ¹³C signals of stored sugars from the previous year. Latewood was subsampled for the years 2009-2019, with an average of five slices per ring. Individual slices weighing between 100-120 micrograms each were extracted with a razor blade under a binocular microscope and then wrapped in tin capsules for δ¹³C analysis. Our ongoing work will include correlation and trend analysis of latewood δ¹³C values within each tree, between trees, and with local weather station records. This work will help to generate local, seasonal climate records that can extend beyond the instrument record in the Shenandoah Valley.