We assessed the influence of overstory trees and abiotic environmental factors on the patterns of spatial variation and species composition in the sapling community of an old-growth Fagus-Acer forest in southwestern Québec, Canada. Our 10 square km study site at Mont St. Hilaire lies at the northern edge of the Deciduous Forest Biome and is the largest remnant of the original forest cover in the St. Lawrence River Valley. We studied differences in the distribution of Fagus grandifolia and Acer saccharum saplings, the two codominant species in the forest canopy. Acer saccharum saplings occurred on a wide range of soil moisture conditions, while F. grandifolia saplings were absent in dry habitats. Acer saccharum saplings were not found on sites where F. grandifolia trees dominate the overstory, while F. grandifolia saplings are mostly limited to these sites. Sites dominated by F. grandifolia have low soil pH and low Ca-availability. We discuss these findings in light of alternative hypotheses on canopy tree replacement patterns in Fagus-Acer forests.

Key words: Acer saccharum, codominance, Fagus grandifolia, forest regeneration, old-growth forest, ordination