Impacts of invasive tall grass Miscanthus sinensis on coastal dune plant communities: a 17-year study in Northern Japan
摘要
Natural coastal dune vegetation has changed drastically worldwide due to the stabilization of dune systems and the expansion of invasive plant species. On Ishikari Beach in Hokkaido, northern Japan, an invasive tall grass, Miscanthus sinensis, has rapidly expanded into the coastal dune grasslands. The purpose of this study was to clarify the temporal changes in the community structure and the responses of major coastal species to M. sinensis invasion. We investigated the species composition and abundance of individual plant species in a 100 m2 survey plot over 17 years (2000–2017). Miscanthus sinensis increased the abundance by around 2006 and then maintained the highest cover of all species, during which a native dominant coastal dune grass, Leymus mollis, highly decreased. Additionally, other inland grasses expanded their distribution ranges into the communities dominated by M. sinensis. By 2017, the total cover of these invasive species exceeded 70%. Non-metric multidimensional scaling ordination analysis (NMDS) revealed that the coastal dune vegetation has shifted to a homogeneous grassland dominated by non-coastal graminoid species. Light conditions at the ground level were significantly darker in areas dominated by M. sinensis than in areas dominated by L. mollis. However, many coastal species survived, despite a decrease in their abundance. Coastal plants with horizontal rhizomes and creeping stems escaped from the shading stress by invasive grasses owing to their flexible mobility. Although the major species are replaced by non-coastal plants, the species diversity of coastal plants is maintained because of their high mobility in the dune grassland.