The aim of the study is to evaluate differences occurring in the soil humus horizons between different types of forests. Soil samples were collected from spruce monoculture and natural beech sites within the lower montane zone in the Tatra Mountains. They were analyzed for organic carbon (OC), loss on ignition in ectohumus horizons, pH, fractional composition of organic matter and cellulose decomposition rate. The objects of investigation are two profiles representing Rendzic Leptosols under spruce and beech, one profile formed on cover bed, which can be classified as Haplic Leptosol under spruce forest and one Haplic Cambisol under the beech site. It is shown that different tree species strongly affect features of both ectohumus and endohumus horizons. This is visible in morphology of humus horizons as well as humus fraction composition which leads to acidification and to a descending cellulose decomposition rate. Another factor controlling features of humus horizons is parent material. It seems to be possible to separate effects which are results of vegetation and parent material features.