AN 802-YEAR TREE-RING CHRONOLOGY FROM THE QUEBEC BOREAL FOREST

On the rocky shores and islands of Lake Duparquet, in the southwestern Quebec boreal forest, Thuja occidentalis L. reaches ages in excess of 800 years. Annual ring widths from 38 trees were used to develop an 802-year chronology (1186-1987) standardized by polynomial regressions. Excellent cross dating, correlation with a shorter chronology located 14 km inland, and 33.6% common variance in a chronology subsample all point to the existence of a climatic signal. After autoregressive modeling to obtain a serially random residual chronology, correlation and response functions were used to identify the growth-climate relationship. The resulting model reduced 19.2% of the chronology variance. Precipitation in June as well as low temperature in June or July seemed to have a positive influence on growth. Likewise, a drought index was closely related to growth, indicating that the chronology could be used to estimate past drought conditions. Moisture deficits are thus inferred for the 13th century as well as during the Little Ice Age (17th century to late 19th century). Since the end of the latter period, precipitation seems to have followed an upward trend.