Average plant species richness in F. japonica plots was 50%lower compared to control plots. This reduction was significant for woody species as well as for herbaceous species. However, species richness of early flowering annuals did not differ significantly. Among the species most affected by knotweed were hop (Humulus lupulus) and European spindle tree (Euonymus europaeus) but also stand-forming species such as nettle (Urtica dioica) or ground elder (Aegopodium podagraria).
Average snail species richness was significantly reduced in F. japonica plots. The reduction was pronounced in large (鈮? mm shell size) and long-lived (>2 years) snail species but not in slugs or small and short-lived snails. For example, large snails such as the Roman snail (Helix pomatia, 鈭?5%) or the red-listed species Bradybaena fruticum (鈭?3%), showed reduced abundances in F. japonica compared to control plots. In contrast, the red-listed but small Vertigo pusilla (+92%) had higher abundances in F. japoinca plots. Principal component analyses revealed little overlap in plant communities or community composition of large snail species between F. japonica and control plots. Taken together, knotweed invasion decreased the cover of most plant species and abundance of large and long-lived gastropods.