Soil and Vegetation Characteristics Associated with the Invasion of Humulus japonicus in Riparian Zones

Abstract

Riparian zones are frequently exposed to floods and artificial disturbances, promoting the invasion of aggressive native plant species. Humulus japonicus is particularly dominant in Korean riparian areas, where its vining habit enables it to overgrow surrounding vegetation. Despite being designated as an ecosystem-threatening species by the Ministry of Environment, ecological insights into its invasive success remain limited. We compared soil and vegetation characteristics between sites invaded and uninvaded by H. japonicus to identify habitat preferences. Additionally, we assessed sex ratios and seed banks, which are critical for the maintenance of dioecious annual plant populations like H. japonicus. Uninvaded sites had significantly higher coverage of perennial plants, and the coverage of H. japonicus was negatively correlated with that of perennial plants across invaded sites. In contrast, the coverage of annual and biennial species was positively associated with the presence of H. japonicus. Among soil characteristics identified by canonical correspondence analysis as explanatory variables for species composition, soil water content was higher in uninvaded sites than in invaded sites. These results suggest that the establishment of H. japonicus is associated with the structure of riparian vegetation and soil water content, although the causal relationships among those remain unclear. No viable H. japonicus seeds were found in uninvaded soils, and only a small number were detected in invaded sites, indicating that seed dispersal from upstream may play a critical role in maintaining population size. The biotic and abiotic factors identified in this study warrant further investigation to clarify their causal roles in the invasion of H. japonicus through manipulative experiments. © The Author(s), under exclusive licence to Korean Society of Plant Biologist 2025.