A 15-month study in a beech forest and alder forest in a nature reserve Buki nad Jeziorem Lutomskim revealed the presence of 36 land gastropod species of 14 families. Euryoecious species and forest species of European distribution dominated. The mean density of gastropods in the beech forest was 36 indiv./m², in the alder forest 27 indiv./m². The density in the beech and alder forest was the highest in winter, the lowest in summer. A highly significant correlation was found between the density and the number of species. In the beech forest malacocenosis, the superdominant was Discus rotundatus (O. F. Müller), the eudominant being Cochlodina laminata (Montagu). In the alder forest, no superdominant could be distinguished, the eudominants being Discus rotundatus (O. F. Müller) and Cochlodina laminata (Montagu). Dominant species, as well as the number of species, species diversity, equitability and frequency varied between months. In the beech forest Discus rotundatus (O. F. Müller) – an accessory species – showed the highest frequency; in the alder forest all species were accidental. Juvenile individuals were more numerous than adults in spring samples from the beech forest and in autumn samples from the alder forest.