Influence of the size and density of Carpinus betulus on the spatial distribution and rate of deletion of forest-floor species in thermophilous oak forest

The change in the species richness following a gradual invasion of Carpinus betulus in the patch of oak forest (Potentillo albae-Quercetum) in Biaowiea was studied between years 1980 and 1994. Species richness and species deletion were compared to the spatial variation in the density and size of C. betulus individuals. The study showed that, in a microscale, (1) the rate of deletion of heliophilous species was similar to that of shade-tolerant ones and was c. 2 species per 4 m² per 10 years, (2) species richness was negatively correlated with the density and size of C. betulus saplings recruited to the shrub layer, (3) species deletion was positively correlated with the number of saplings in the shrub layer. The results support the hypothesis that the invasion of C. betulus is a proximate cause of the decline of Potentillo albae-Quercetum, and in a microscale, it has three stages: (a) initial colonisation of the ground layer by the seedlings, (b) recruitment of juveniles to the shrub layer, deterioration of light conditions and rapid deletion of species, and (c) closure of the canopy and deletion of remaining heliophilous species and vulnerable shade-tolerant species. Nomenclature: follows Ehrendorfer (1973) and Matuszkiewicz (1981).