Vegetation and environmental changes in a Scots pine forest invaded by Prunus serotina: What is the threat to terricolous bryophytes?

In the pine forests of Central Europe, a wide and quick spread of Prunus serotina was observed. However, the impact on invaded phytocenoses is still unclear. In selected Scots pine forests with black cherry (SW Poland), the vertical forest structure and floristic composition of the herb and moss layers were studied by sampling permanent relev,s in 2003 and 2013. To investigate the understorey vegetation changes, the plant cover and the alpha and beta diversities were used. Habitat features were expressed using Ellenberg's indicator values (light, soil moisture, soil reaction and nitrogen availability). It has been shown that as a result of the expansion of black cherry, there have been changes in the vertical structure of the forests that are associated with the creation of a highly developed layer under the canopy of pine trees. This layer showed a strong negative correlation with the number of understorey species. Based on redundancy analysis, it was found that P. serotina cover in the canopy layer explained 11 % of the total variation in the species composition. It has been demonstrated that there has been a retreat of typical pine forest taxa, especially the terrestrial mosses (e.g. Dicranum scoparium and Pleurozium schreberi). In addition, the presence of P. serotina favoured understorey colonisation by synanthropic species (e.g. Taraxacum officinale, Calamagrostis epigejos and Impatiens parviflora). The reported changes in indirectly estimated environmental factors in the test interval were related to increased nitrogen availability and a decreased light index. The influence of black cherry on shading the forest floor, litter production, nitrogen enrichment of the habitat and decline of terricolous bryophytes is discussed.