Changes in the understorey of mixed coniferous forest plant communities dominated by the American black cherry (Prunus serotina Ehrh.)

• In managed European forests progressive expansion of Prunus serotina is observed.
• Effect of P. serotina invasion on the forest understorey community was studied.
• Rising P. serotina abundance in shrub layer reduces understorey species number.
• P. serotina expansion has significant effect on understorey species composition.
• Impact of P. serotina explains only a part of the species composition variability.

In the managed mixed forests of Europe, Prunus serotina increases its territory easily and gradually becomes the predominant component of the shrub layer. However, its impact on species diversity in the invaded stands remains a matter of debate. To assess the relationship between the black cherry and the understorey plant community, 120 relevés of comparable habitat properties but of variable intensity of infestation by P. serotina were made in three forest districts in south-western Poland, where the plant has been present for more than 50 years. Habitat features were estimated indirectly for study plots using selected Ellenberg’s species indicator values (nitrogen availability, soil reaction, soil moisture and light conditions). The forest floor of the areas infested with black cherry showed higher proportions of certain plant species with higher requirements for nitrogen supply, soil reaction and moisture content. Furthermore, a significant negative correlation has been found between the abundance of P. serotina and the species richness of the understorey. Also in multiple regression analysis black cherry occurring in the shrub layer has appeared as the variable significantly related to the decrease of species number. Despite those established relationships, feeding species composition data into the redundancy analysis (RDA) procedure showed that the black cherry’s impact on the herb and moss layer explained only a limited proportion of the general variance. Therefore, it is likely that the effect of P. serotina on the native species composition in different forest stands is significantly modified by a set of site-specific environmental variables, interacting with a number of disturbances caused by natural factors and human activity.