Geospatial data layer of seminatural grasslands with century-old or longer temporal continuity

Grasslands in Japan, once covering over 10% of the national land, have rapidly declined due to land-use change and the abandonment of traditional management, resulting in the loss of biodiversity and associated ecosystem services. Because the ecological value of grasslands is closely tied to their temporal continuity, identifying long-persisting sites is crucial for effective conservation and restoration planning. However, such assessments have so far been limited to local or regional scales due to the lack of comprehensive historical datasets. This study presents a national-scale geospatial dataset of century-old seminatural grasslands in Japan, constructed by integrating multiple sources of historical and contemporary spatial data. We combined long-term land-use and vegetation information to trace changes in grassland distribution over more than a century, linking modern high-resolution datasets with historical land-use maps and expert knowledge on long-maintained grasslands. By assessing the overlap between historical and recent grassland distributions, we identified areas that have persisted for over 100 years and remain maintained as seminatural systems through human management. The resulting dataset comprises 2,654 polygons representing seminatural grasslands with over a century of continuity across Japan. This dataset provides the first nationwide distribution records of grasslands with long term temporal continuity, supporting conservation prioritization, biodiversity monitoring, and landscape-scale restoration efforts of grasslands. The data are openly available under non-commercial license in GIS-compatible formats to facilitate broad research and policy applications.