Author(s): Yota Imai, Natsuko Shigehara, Shozo Shibata, Yasunori Muto, Mahito Kamada

Linked Author(s): Yasunori Muto, Mahito Kamada

Keywords: Hydraulic condition; Inundation simulation; Paddy fields abandonment; Wetland vegetation;

Abstract: Paddy fields have been developed on floodplain and kept as an annual grassland in terms of rice cropping. Recently, however, wide area of paddy fields has been abandoned year by year, at depopulating region in particular. In the situation, it is assumed that wetland vegetation can recover at abandoned paddy fields and kept in natural hydraulic process. A purpose of the study is to clarify spatial relationship between plant communities and hydraulic conditions, based on a hypothesis that different types of plant community appear along environmental gradient, in terms of difference of depth and time duration of inundation. Target floodplain of 12 ha is in Shitaru, Tsushima Island, Nagasaki Prefecture, Japan. The area, ca. 12 ha, was kept as paddy fields until the 1960s. Almost entire area, however, has changed to wetland vegetation nowadays. Vegetation map of 2010, was used for analysis. Topographical map was produced by measurement with UAV and GNSS. Using iRIC Nays2DFlood (ver.5.0), two-dimensional flood flow analysis was conducted and maps indicating hydraulic conditions were produced. Then occurrence pattern of plant communities was analyzed by overlying the vegetation map with the hydraulic condition maps. The results show that abandonment of paddy fields has caused channel formation and made spatial difference in hydraulic condition, then encourage the spatial formation of plant communities; emergent and hygrophyte plant groups are established near the channels where maximum depth of inundation is deep and its time is long, while plant communities of terrestrial type are established at area distant from channels where depth of inundation and its time are little.

DOI: https://doi.org/10.3850/38WC092019-1654

Year: 2019