Land-cover changes and distribution of wetland species in small valley habitats that developed in a Late Pleistocene middle terrace region

Abstract

Small valley topology on terraced uplands is a unique groundwater-dependent ecosystem in East Asia. Traditionally, this characteristic valley topology has been used for rice paddies because of the sustained availability of spring water. It also provided a unique habitat for wildlife with moderate agricultural disturbance. Due to recent changes in the land use of terraced terrain, these semi-natural wetlands are disappearing rapidly without an accurate assessment of its conservation value. We examined the distribution of small valley habitats in the Shimousa Upland in northern Chiba Prefecture, Japan, and analyzed temporal changes in land cover from the 1970s to 2010s. We also compared the habitat affiliation of endangered wetland species in the small valley topology and the temporal change of their habitat suitability. We found that the relative percentage of urban area has increased rapidly in upland (from 18.6 to 37.9%) and valley (from 13.1 to 28.6%) areas. The abandonment of rice paddies in the valleys has also increased. Of the endangered wetland species, Geothelphusa dehaani, Lefua echigonia, and Lethenteron reissneri were more common in small valley wetland habitats. However, remained habitat for these species has been decreased due to the on-going urbanization in a terrace area.