Possible mechanisms of sugar maple regeneration failure and replacement bybeech in the Boise-des-Muir old-growth forest, Quebec

To better understand the causes of sugar maple (Acer saccharum Marsh.) repl acement by beach (Fagus grandifolia Ehrh.) in the Boise-des-Muir old-growth forest (Quebec), we studied, i) the effect of beech litter on soil propert ies, ii) the effect of low light availability on maple survival and iii) be ech regeneration via root sprouts. Soil properties, understory light, seedl ing emergence and survival, height growth, and density distribution of mapl e and beech were compared between the old-growth stand and an adjacent mana ged stand where the abundance of maple regeneration was high. We did not ob serve any detrimental effect of beech litter on soil properties and maple e arly establishment. Overall light availability and maple stocking were lowe r. and maple density declined more markedly with increasing size in the aid -growth stand than in the managed stand. The deficient maple regeneration i n the old-growth stand might be related to a lack of microsites where light availability is high enough for maple survival, and not to a lack of initi al recruitment in this species. In the old-growth stand, beech was located in mon shaded microsites than maple hut had a higher growth. Size class dis tributions of maple and beech suggest that beech had a higher survival rate than maple and that beech sprouts had a higher survival rate than beech se edlings. Beech seems to be better adapted than maple to survive in the deep shade of the old-growth stand. However, we expect that maple will regain i ts dominance in the understory of the Boise-des-Muir with increasing stand breakup that is likely to occur in the future.