Natural revegetation potential of Japanese wild thyme (Thymus quinquecostatus Celak.) on serpentine quarries

Quarrying is an important industry that supports human infrastructure, but it has negative effects on human health, environments, and plant communities. In the case of the serpentine quarry on Sugashima Island (Sugashima), Japan, rapid remediation using native plants is necessary to restore the serpentine ecosystem. According to our previous work, we revealed high adaptability of Japanese wild thyme (Thymus quinquecostatus Celak.) to the severe environment of serpentine areas, and we desired to utilize this species for revegetation. However, basic information on Japanese thyme was extremely limited, in comparison with well-investigated European thymes that have been used for revegetation experiments. The aims of this work were to identify the plant functional traits of wild thymes collected from different areas of Japan and to test their potential for revegetation of serpentine quarry soil. We collected four types of wild thyme from Sugashima and other areas of serpentine, calcareous, and tuff breccia soil, and revealed varietal differences in leaf form, branching patterns, flowers, and also blooming season, seed formation ability, and seed germination percentages. Thymes from serpentine and calcareous areas could grow on soil of the serpentine quarry, and a small number of plants were able to cover the experimental plots. Among the Japanese thymes investigated, Sugashima thyme had the longest branches, and spread rapidly by forming many branches. These data suggest that Japanese thymes, especially Sugashima thyme, have good potential for revegetation of serpentine quarries.