The intertidal zones of the Tsuyazaki Inlet were investigated to determine the groundwater salinity in the reed marsh and non-reed-marsh areas. From May 2021 to April 2022, conductivity data loggers were set up at three survey sites in the reed marsh area, the non-reed-marsh area, and the water channel. The daily range in salinity was smaller in the groundwater than in the channel water. Groundwater salinity was significantly lower in the reed marsh areas than the non-reed-marsh areas. The reed marsh area is adjacent to small mountains and the non-reed-marsh area is adjacent to a flat plain, suggesting that the amount of subterranean freshwater differs depending on the terrestrial topographic conditions, which influences the salinities of the groundwater. Moreover, seven and five survey sites were established in the reed marsh areas and non-reed-marsh areas, respectively, and the salinity of the surface water and groundwater was measured in December 2021 and July 2022. The median salinity of the surface water and groundwater in the non-reed-marsh areas exceeded 28.0 ppt, which was almost equivalent to the salinity of seawater. The median salinity of the groundwater was significantly lower in the reed marsh areas than the non-reed-marsh areas. Moreover, the median salinity of the groundwater in the reed marsh areas was in the range where the germination and growth of reeds were possible. Our findings suggest that the groundwater in the reed marsh areas is stable and has lower salinity than the groundwater in the non-reed-marsh areas. Further studies of the groundwater salinity of intertidal zones are expected to help in the selection of more effective candidates for reed marsh restoration areas.

Adonis ramosa is a perennial plant belonging of Ranunculaceae and grows mainly in deciduous forests. It is distributed from central to southern Hokkaido, Honshu, and Shikoku, and is an endangered species in many prefectures. In order to effectively and efficiently conserve A. ramosa, it is one of the important issues to understand the habitat conditions of A. ramosa. Although previous studies reported the effects of light conditions on A. ramosa, no study has evaluated the local factors and the relative importance affecting the habitat conditions of A. ramosa. In this study, we evaluated the habitat condition of A. ramosa in central and southern Hokkaido, focusing on environmental factors including conditions of light, soil, litter, and surrounding vegetation. In April and May of 2021, the flowering and fruiting season of A. ramosa in central and southern Hokkaido, we set up 5 quadrats (1 m × 1 m) of each study site (7 sites in total), and counted A. ramosa abundance in a total of 35 quadrats. Also, we measured environmental factors (relative illuminance, soil hardness, litter depth, floor cover, and canopy cover). The results showed that A. ramosa abundance was positively affected by relative illuminance, and negatively affected by litter depth and floor cover. These results suggest that it is important to focus the environment with bright light, thin litter layer, and little floor vegetation in order to conserve A. ramosa. If A. ramosa habitat has to be modified due to development, it is necessary to transplant A. ramosa to such environment. In the case of monitoring and maintenance of A. ramosa habitat, mowing and raking fallen leaves are considered to be effectives.

Tree cover has recently expanded in floodplains and riparian areas, and river administrators cut the trees and excavated the areas for flood management in Japan. Trees, such as willows, recolonize and expand quickly on bare land after the work but little information is available on the speed at which trees expand. We examined the expansion rates of the tree cover on the bare land after the excavation and the differences in the rates depending on the slopes of the riverbed. We estimated temporal trends in the area covered by the willows using aerial and satellite photographs at 26 reaches located in alluvial plain. The expansion rates of the tree cover increased rapidly 5 years after the excavation. Thereafter, about 50％ of the excavated area was again covered by trees in 10 years. After about 5 years, some individuals are considered to have grown to a size that could cover the parts of the bare lands with their canopy, likely leading to a rapid increase in the area covered by trees. The expansion rate was faster in reach with a gentle slope than a steep slope. Trees are less likely to be destroyed owing to the low flow velocity on the gentle slope. We demonstrated the tree expansion rates on the excavated bare land, and our findings contribute to decisions on when the river administrator should cut trees and excavate the tree-covered area again.