Impact of northern red oak Quercus rubra L. on ferns populations in different forest phytocoenoses

Northern red oak (Quercus rubra) is the most common alien tree species in Polish forests that is considered as an invasive one. It is native to North America. Negative impact of Q. rubra on natural habitats in Europe is well-known, but there is still a lack of information about correlations between red oak and individual species or groups of plants. Especially knowledge about impact of Q. rubra on fern communities is still unsatisfactory. The goal of research was to check if ferns could be neutral to the negative oak impact. In order to verify, populations of ferns occurring in patches of forests dominated by northern red oak and population from natural forests with the same abiotic conditions were compared. Moreover, quantitative relations between ferns and other herb species were analyzed. The research was carried out in southern Poland. Field surveys were conducted in 100 m(2) plots with domination of Q. rubra. Plots were settled in 3 different types of plant communities: mixed broadleaf forest, acidophilous oak forest and acidophilous beech forest. In the same types of plant communities, but without northern red oak; control plots were located. Control patch was settled in place with similar inclination, exposition, altitude and water regimes. For each surface list of all herb species with their percentage coverage and biometric measures of fern fronds were made. At maximum. 50 specimens of each fern species were taken into account. Plots were located in areas of 3 geographical regions: the Slaskie Foothills, the Oswiecimska Basin and Slaska Upland. Results show that ferns in monocultures of the alien oak are bigger, more lush and their coverage is higher than in the control plots. What is more, coverage of other herb species and species diversity are significantly higher in control patches. It suggest that ferns are not sensitive to Q. rubra influence, so it can be concluded that they are competitive to other species which are sensitive to northern red oak impact.