نبذة مختصرة : A field survey was conducted from April 2023 to April 2024 to assess the current flora and distribution of threatened plant species in Ijimino Hill, Shibata City, Niigata Prefecture, Japan, including Masugata pond and its surrounding wetlands. Over a survey period of 22 days, 77 person-days were invested. A total of 534 taxa, comprising 468 native and 66 alien taxa (12.4%), were recorded. Of these species, five are listed on the Japanese national Red List, and 25 are included in the Niigata Prefectural Red List. Compared to previous surveys, we documented 75 new taxa, including 18 alien species. Notably, Pogostemon yatabeanus and Sparganium subglobosum were rediscovered after 37 and 25 years, respectively. However, we did not observe 246 taxa, including 20 endangered species and 15 aquatic plant species. In the wetland vegetation, Alnus japonica was the dominant tree species. Areas with open canopies, such as those near water bodies, boardwalks, and trails, exhibited a higher relative light intensity compared to the central wetland and valley areas (14.70% ± 1.85%). A positive correlation was found between relative light intensity and both the number of species (p < 0.01) and Simpson’s Diversity Index (p < 0.01). These findings provide insights into the changes in the flora of Ijimino Hill and suggest that potential improvements to the light environment can be achieved by thinning dense stands of A. japonica. ; departmental bulletin paper
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