Land use changes, such as urbanization and agricultural expansion, are expected to cause drastic changes in the spatial distribution of vascular plant species. This study quantitatively assessed the temporal trends in site number dynamics of 1,865 native vascular plant species in Kanagawa Prefecture, a region adjacent to the megacity of Tokyo. The assessment was based on presence-absence data for 1,865 species, accumulated through three systematically conducted citizen science surveys. The surveys divided Kanagawa Prefecture into 104 administrative districts, recording the presence or absence of targeted species in each district.
The survey period consisted of three phases: Phase 1 (1979–1989), Phase 2 (1996–2000), and Phase 3 (2013–2017). The number of districts with recorded presence was counted for each species in each phase. Trends in the number of presence records were classified into five categories: sequential decrease (SD), fluctuating decrease, sequential increase (SI), fluctuating increase, and no change. As a result, 433 species were classified as SD, while 386 species were classified as SI. To investigate which habitat types are associated with SD and SI species, we classified the target species into 12 habitat types. We then conducted chi-square tests to compare the proportion of habitat types between SD and the remaining categories, as well as between SI and the remaining categories. As a result, species classified as SD had significantly higher proportions in grasslands, paddy fields, forest edges and wastelands compared to the remaining categories. In contrast, species classified as SI exhibited a significantly higher proportion in evergreen forests than in the remaining categories. Therefore, grasslands, paddy fields, and forest edges are likely affected by change in land use. Among the species that inhabit evergreen forests, ferns and mycoheterotrophic plants increased significantly, likely due to the succession of coppice forests following the abandonment of traditional management. In conclusion, land-use change contributed to both habitat loss for some species and habitat expansion for others, with significant associations with habitat types.