Evaluating Native Grassland Species for Application in Extensive Green Roofs in Japan

Extensive green roofs (EGRs) are increasingly recognized as multifunctional components of urban green infrastructure. In recent years, interest is growing in the use of native grassland species as alternatives to conventional green roof plants, both to enhance ecological function and to support biodiversity conservation. This study evaluated the performance of six native grassland species on extensive green roofs by assessing their growth characteristics (cover, survival, and flowering) throughout a single growing season (May–November 2024). We used three different substrates that differed in nutrient level: a nutrient-rich reused substrate, a mixed substrate, and a nutrient-poor perlite-based substrate. The results indicated that most species successfully established across all substrate types, although patterns in growth and mortality varied. Substrate nutrient levels strongly influenced early growth, but their long-term effects may diminish as nutrient dynamics stabilize over time. These findings suggest that native grassland species represent promising alternatives to conventional green roof plants in Japan, with several species showing strong adaptability to EGR conditions. Substrate nutrient management is essential for balancing plant growth, biodiversity, and maintenance requirements. This study contributes to improving the ecological performance and long-term sustainability of green roofs in urban environments.