VARIATION IN INTRA-ANNUAL RADIAL GROWTH (XYLEM FORMATION) OF PICEA MARIANA (PINACEAE) ALONG A LATITUDINAL GRADIENT IN WESTERN QUEBEC, CANADA

. Premise of the study : Climate warming might have resulted in altered initiation and termination dates of stem xylem growth in boreal stands. A systematic understanding of intra-annual xylem formation is thus needed for precise simulation of future growth in the context of sustainable forest management. . Methods : A recently developed novel microsampling approach was employed over two growing seasons (2005-2006) to investigate the intra-annual stem xylem formation of Picea mariana at three sites along a latitudinal gradient (approximately 47.5-5 degrees N) in western Quebec, Canada. The critical timings of xylem cell formation were determined and compared among sites/years. The relationships between xylem cell formation and meteorological variables were examined. . Key results : From south to north, the onset of xylem cell production was detected on 20 May (SD +/- 3) at Angliers, 24 May (SD +/- 3) at Chicobi and 24 May (SD +/- 4) at Muskuchii in 2005, and on 12 May (SD +/- 4) at Angliers, 14 May (SD +/- 3) at Chicobi and 20 May (SD +/- 3) at Muskuchii in 2006, respectively. Xylem cell production at each respective site terminated on 11 August (SD +/- 4), 7 August (SD +/- 3), and 7 August (SD +/- 4) in 2005, and on 8 August (SD +/- 4), 4 August (SD +/- 4), and 4 August (SD +/- 4) in 2006, respectively. . Conclusion : Our study implies that despite the expected occurrence of earlier phenological development due to early spring climate warming, boreal trees like P. mariana might not be producing wider rings if cold temperatures occur later in the growing season in June to August. These results may challenge the view that boreal trees could be benefiting from spring warming to enhance growth.