Paper No. 4
Presentation Time: 8:00 AM-12:00 PM
EVENT DENDROCHRONOLOGY AS A RECORD OF INTENSE HISTORICAL STORMS ALONG ASSATEAGUE ISLAND, MARYLAND
In addition to chronological information within annual tree rings, long-term patterns and individual ring widths may provide information about distinct events. In coastal regions, a noticeable decrease in ring width often results from stress, which can be geological (intense storms, fires, excessive erosion or deposition, dramatic water-table fluctuations) and biological (disease, infestation, competition) in nature. Fifteen pine tree (Pinus taeda) cores from three locations on Assateague Island, MD, were examined using standard dendrochronological techniques and image analysis software. For each tree core, a stress index was determined by scaling all ring widths to the narrowest and plotting the reciprocal values. Therefore, a sharp increase reflects an abrupt stress, with peaks representing short-term perturbations in tree growth. Whereas there are overall trends toward narrowing of the rings in most samples, decade-normalized values are not useful in revealing discrete events due to the arbitrary nature of each sub-sample boundary. Therefore, standard annual histories were used to document the timing and relative magnitude of environmental stress events, which we interpret as the impact of saltspray, excessive winds, and flooding during intense storms. Seven tree samples that exceed 50 years in age, display a prominent 1962 peak, which coincides with the March nor’easter – the Ash Wednesday Storm of record for this region. A number of smaller peaks correlate with intense hurricanes of 1938, 1954, and 1992, with a delayed ecological response likely due to the occurrence of tropical storms late in the growth season (July –November). The physical setting (distance from the ocean and backbarrier, elevation) may further explain a variable dendrological response within each sampling location. Similar trends have been described for Parramore Island, VA and have been documented in preliminary examination of juniper samples from coastal New Jersey. All tree cores were also analyzed using Image J software to quantify the grey-scale values of the complete ring sequence. Whereas the ring pattern was not as evident in the alternating color plot, the spatial distribution of points with sharpest contrast (between latewood and a subsequent earlywood) has the potential to be used as an efficient proxy for ring width.