Canada is a country, on the northern part of North America. 46% of land is covered by forest. Quebec is the biggest Canadian province with the highest woodiness. In the group of the most important hardwoods of Quebec, we find sugar maple and yellow birch. Areals and ecological needs are almost the same or both species. In spite of that, we can find around the forests much more sugar maples than yellow birches. Forests owners try to increase the percentage of yellow birch, as this tree is commercially much more interesting. This thesis tries to illustrate how the light conditions in such forest type influence regeneration. We studied two objects on different locations, but on the comparable site. First object was a managed forest and the other was a virgin forest (old-growth forest). On both objects, gaps have already been chosen. Diferent parameters were measured in gaps and under canopy for both species. Received data were analysed with statistical program SPSS. Results shows, that management was inappropriate. Shelterwood was not a good silvicultural system. It allowed too much light to enter the forest, which heavily stimulated the growth of sugar maple. Yellow birch successfully competes with sugar maple in the low light condition but slenderness and relative increment prove that yellow birch is less shade tolerant. The reason why we did not find the difference in virgin forest is low light range, the reasons in managed forest are: low number of seed trees, heavily browsing and lack of large old wooden part. Crown closure should be more closed in managed forest. Achieving this, we should practise group selection cutting and form gaps, which are smaller than one tree height.