The influence of invasive Fallopia taxa on resident plant species in two river valleys(southern Poland)

Riparian zones in two rivers in southern Poland were studied in terms of species composition and soil parameters in patches dominated by three knotweed taxa (Fallopia japonica, F. sachalinensis and the hybrid F. ×bohemica). The main purpose was to detect any differences in species diversity, environmental conditions and in the impact of the three Fallopia spp. on resident species. Fieldwork was conducted in spring and summer in 30 invaded plots (in total 90 subplots). It was demonstrated that vegetation dominated by particular knotweed taxa differed in response to soil pH and ammonium, nitrate, and magnesium content. Fallopia spp. (living plants and necromass) had a stronger negative impact on the cover and species diversity of the resident species in summer in comparison with spring. Vegetation patches differed significantly in species composition in relation to the knotweed taxa present. These differences may be the consequence of the differentiated biotopic requirements of Fallopia taxa and the coexisting plants, or to the different impact of the knotweed taxa on the resident species