Comparative dendroclimatological analysis of two black ash and two 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 (Thuja occidentalis L.) growing in contrasting sites in the Abitibi region of Quebec. An indexed mean chronology of radial growth was developed in each case. Black ash from flooded sites did not cross-date with those 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 the growing season also had a negative impact on the following year's growth, whereas a high drought index during June of the preceding year (i - 1) had a positive one. Radial growth of unflooded black ash is mainly related to temperature. For those black ash not exposed to flooding, the preceding year's August temperature (i - 1), as opposed to August 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 current year's growth. Compared with black ash, white cedar from both xeric and mesic sites showed good between-site cross dating and had similar relationships to climate. In both cases, abundant summer precipitation, associated with cool temperature, produced maximum growth. Temperature during August of the preceding year (i - 1) was also negatively correlated with radial growth. White cedar from xeric sites also responded more intensely to drought, as revealed by the negative relationship to the June-July (i) drought index. In conclusion, growth-ring analyses show the specificity of the climatic response of these two species and the filtering effect caused by different environments.