Floodplain forest vegetation in the northern part of the Western Carpathians

Floodplain forests, as diverse plant communities commonly related to riparian zones, host plant species with various ecological niches and origins. The phytosociological context of floodplain forests has been well described on national level in many European countries, however, there are still regions with relatively poorly known variability of their species composition and environmental drivers controlling their vegetation patterns. Vegetation sampling of floodplain forests using traditional European phytosociological approach along with the recording of environmental (climatic, edaphic, topographic) variables was carried out in the northern part of the Western Carpathians (Slovakia and Poland) in period of 2011–2016. We gathered dataset of 135 original phytosociological releves, which were classified using modified TWINSPAN algorithm. Five associations were distinguished: (i) meso-eutrophic black alder swamp forests (Carici acutiformis-Alnetum glutinosae), (ii) montane oligotrophic mixed spruce-alder forests on waterlogged sites (Piceo abietis-Alnetum glutinosae), (iii) riparian willow forests (Salicetum fragilis), (iv) meso-hygrophilous riparian alder forests (Stellario nemorum-Alnetum glutinosae) and (v) riparian grey alder forests (Alnetum incanae). Canonical Correspondence Analysis (CCA) with forward selection was used to show effect of environmental factors on species composition variation. The explained variance declined from marginal (13.9%) and conditional (8.6%) to pure effect (7.5%), with altitude (1.6%), total soil nitrogen content (1.6%) and soil pH (1.4%) being the most important predictors accounted for the highest variation in species compositional data.