Effects of the tree layer on the ground cover, including the spatial distribution of individual species and their combinations (microgroupings), were analyzed in eight sample plots located in different forest types in the "Kivach" strict nature reserve. Mosaicity of the ground cover, understood here as the diversity of species combinations, was found be the most explicit in seral communities, especially in secondary deciduous ones. As forests in areas with relatively low mesorelief mature, mosaicity appears as the recurrence of few types of microgroupings, the degree of its manifestation in pine and spruce forests being different. Thus, in mature pine forests it is in fact visible at the level of the moss-lichen layer only. Heterogeneity of the ground cover in mature spruce forests is far more conspicuous due to the greater effect of spruce trees on the environment.