Non-native plant species in alder-dominated forests in Slovakia: what does the regional- and the local-scale approach bring?

European riparian forests are in general susceptible to plant invasions compared to other natural forest habitats. Their descriptive vegetation overviews with phytosociological affiliation contain detail insight into species composition patterns at various geographical scales, but quantitative assessment of the relationship between non-native plant richness and measured environmental variables is still scarce. We used two vegetation datasets of alder-dominated forests to analyse plant invasion patterns in the Pannonian and the Carpathian region of Slovakia. A large dataset of 918 vegetation plots was used at the regional scale, whereas 40 vegetation plots completed by ecological (mainly soil, climatic) predictors were used at the local scale in order to determine how they shape non-native species richness. We found significant differences (P < 0.05) between the Pannonian and the Carpathian region in the number of non-native vascular plants at both scales, with altitude being the most important predictor. Generalized Linear Models accounted for 56.6% and 59.6% of alien species richness data in the Pannonian and Carpathian region, respectively. Alien richness was affected by altitude and soil pH in the Pannonian region, but only by altitude in the Carpathian region.