A 1397-YEAR TREE-RING CHRONOLOGY OF THUJA-OCCIDENTALIS FROM CLIFF FACES OF THE NIAGARA ESCARPMENT, SOUTHERN ONTARIO, CANADA

Living and dead Thuja occidentalis L. (eastern white cedar) on cliff faces and in the talus of the Niagara Escarpment, southern Ontario were sampled and measured for dendrochronological analyses. One hundred and forty-two tree-ring series were cross-dated and a 1397-year tree-ring chronology was produced spanning the period 594-1990 A.D., making it the longest in Canada. An additional 784-year floating chronology was constructed from dead debris at the base of the cliff. Radiocarbon dates indicate that the floating chronology begins approximately in 580 B.C. Correlations between the tree-ring indices and 51 climate variables indicate that growth in T. occidentalis is negatively correlated with the previous growing season's temperature. The strongest correlation was between radial tree growth and maximum temperature in the previous July and August. Extremely hot summer conditions will negatively impact tree growth in the following year. These temperature correlations are very similar to those observed for T. occidentalis growing in western Quebec. This consistent climate response and the extreme longevity of T. occidentalis means that it is now an important species to exploit for dendroclimatological reconstructions of regional climate. The close proximity of these sites to the industrial heartland of eastern North America suggests that this, and future Thuja chronologies under development from the Niagara Escarpment, will provide an important ecological data base for exploring the human component of climate change.