Session

Semi-natural grasslands have traditionally been maintained under human management. As grazing and mowing are labor-intensive practices, grassland management has been increasingly abandoned recently, while prescribed burning has emerged as an effective and efficient method for maintaining larger grassland areas with less effort compared to grazing and mowing. However, semi-natural grasslands managed only by prescribed burning (burned grasslands) tend to have taller vegetation height compared to when combined with other management practices, which leads to lower diversity of low-growing native plant species, especially threatened species. With the increase of burned grasslands, clarifying how high diversity can be maintained in burned grasslands is an urgent issue for conserving grassland plants. Natural grasslands with low vegetation height can be found under unique soil conditions, such as rocky areas with little soil formation. We hypothesized that a high diversity of grassland plants, including threatened species, is maintained in environments with shallow soil and low vegetation height even in burned grasslands. We compared soil environments and plant diversity among burned grasslands underlain by different parent materials, focusing on soil development variations. We conducted vegetation and soil environment surveys in burned grasslands established on several types of parent material. We aimed to test the hypothesis that plant species diversity would be highest in burned grasslands with less developed soils. In the survey, we established 50 1m2 plots in the lava/scoria grasslands of Nashigahara and 40 plots each in Oishi-highland and Kaida-highland. Vegetation surveys were conducted in June and September and soil water content, hardness and depth and rock and stone cover were measured in September. Soil pH and total extractable nitrogen (N) and plant-available phosphorus (P) contents were only measured in Nashigahara. As a result, the youngest lava grasslands in Nashigahara had the shallowest soils, lowest vegetation height and highest plant diversity including threatened species. In Nashigahara, the youngest lava grasslands had the lowest soil pH, but no significant differences in N and P were found between lava and scoria grasslands.