Two sites that burned in 1847 (H) and 1823 (I) in the mixedwood boreal forest in Québec were selected to follow aspen genetic and clonal diversity over time. At each site, three cohorts were identified by core dating, and about 30 trees per cohort were randomly selected to compare tree genotypes using four microsatellite loci. The first cohorts were of post-fire origin (large disturbance), while the second and third cohorts were promoted by gap disturbances. These gaps were created by the natural mortality of post-fire aspen trees and a spruce budworm outbreak that attacked the coniferous species. Expected heterozygosity ranged from 0.37 to 0.72 across cohorts and averaged 0.66 and 0.54 in H and I, respectively. More than 99% and 96%of the genetic variability existed within cohorts, respectively. Genotypic diversity was high in all cohorts, and most genets were unique. Only two clones suckered for three successive cohorts, indicating little selection for specific genets to dominate aspen stands with time. High genetic and clonal diversity changed slightly between post-fire and gap disturbance cohorts. Apical dominance might have favoured the suckering of genets that existed in the post-fire cohorts but that were later eliminated by natural mortality.
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Vol. 12 • No. 1