COMPARATIVE DENDROCLIMATOLOGICAL ANALYSIS OF 2 BLACK ASH AND 2 WHITE CEDAR POPULATIONS FROM CONTRASTING SITES IN THE LAKE DUPARQUET REGION,NORTHWESTERN QUEBEC

The relationship between radial growth and climate was analyzed in two black ash (Fraxinus nigra Marsh.) and two white cedar populations (Th uja occidentalis L.) growing in contrasting sites in the Abitibi regio n of Quebec. An indexed mean chronology of radial growth was developed in each case. Black ash from flooded sites did not cross-date with th ose from unflooded sites and responded differently to climate. On the floodplain sites, black ash radial growth is directly correlated with the previous year's August precipitation (i - 1) and with the current year's June precipitation (i). High water levels at the beginning of t he growing season also had a negative impact on the following year's g rowth, whereas a high drought index during June of the preceding year (i - 1) had a positive one. Radial growth of unflooded black ash is ma inly related to temperature. For those black ash not exposed to floodi ng, the preceding year's August temperature (i - 1), as opposed to Aug ust precipitation, had a negative impact on the current year's growth. A high drought index in June (i) also had a negative impact on the cu rrent year's growth. Compared with black ash, white cedar from both xe ric and mesic sites showed good between-site cross dating and had simi lar relationships to climate. In both cases, abundant summer precipita tion, associated with cool temperature, produced maximum growth. Tempe rature during August of the preceding year (i - 1) was also negatively correlated with radial growth. White cedar from xeric sites also resp onded more intensely to drought, as revealed by the negative relations hip to the June-July (i) drought index. In conclusion, growth-ring ana lyses show the specificity of the climatic response of these two speci es and the filtering effect caused by different environments.