CLIMATE SIGNALS IN A 195-YEAR RED OAK TREE RING RECORD FROM THE CHAMPLAIN VALLEY, NEW YORK

Thirty-two cores were taken from 16 trees in a stand of red oak (Quercus rubra) on the tip of a peninsula on Lake Champlain in Willsboro, New York. Annual ring widths were measured and the resulting series crossdated to form a chronology spanning the years 1814 – 2008. Crossdates were made statistically with the program COFECHA and were verified graphically. The chronology has a mean series intercorrelation of 0.715 and an average mean sensitivity of 0.169.

For climatic analysis, all samples were standardized using a spline with a 50% frequency cutoff of 32 years in the program ARSTAN. The residual chronology, from which persistence had been removed, was then correlated with monthly climatic data from Burlington, Vermont, 18 km to the east. It was found at the 99% confidence level that the red oak ring widths had negative correlation with maximum and average temperatures in June and positive correlation with June and July precipitation. Similarly strong positive correlations were also found with the June and July short term Palmer “Z” drought index (ZNDX) for New York climate division 7. A model of average June-July ZNDX performed well in verification tests on a split data set, with Coefficient of Efficiency (CE) values of 0.32 – 0.45 and Reduction of Error (RE) values of 0.34 – 0.47. These indicate that the model has strong predictive value. Modeled results for years prior to recorded ZNDX measurements suggest that there may have been significant summer drought in the Champlain Valley during the years 1820, 1849-1850, and 1884.