Influence of rice cultivation and its cessation on the vegetation in valleys in hill land in Chiba prefecture [Japan]

Summary This report describes the results of vegetation surveys of herbaceous communities distributed over unconsolidated paddy fields and their surroundings on valley floors in hilly terrain in Chiba Prefecture, Japan. The surveys were performed in areas where rice is cultivated and also in areas containing rice paddies that not been cultivated had for 20 years. There were 112 herbaceous and tree (seedling) species present in the valley where rice was actively cultivated, and stands were classified into five types of landscape based on their topography and type of utilization. In contrast, there were 79 species present in the valley where rice cultivation had ceased, and the stands were classified into three types of landscape. The quadrates surveyed were divided into seven categories at a 50% level of similarity by cluster analysis based upon the relative importance of each species. The categories do not necessarily correspond to landscape elements. The cluster b-1 contains dominant species that were found around footpaths, irrigation ditches, the forest margin, and the forest floor. This result indicates that the floristic composition of cluster b-1 consists of precursor species at the valley site. The dominant species was subsequently divided based on their utilization type. The species richness-diversity relationship in abandoned rice paddies was positively correlated. The landscape elements in areas where rice is actively cultivated were divided into three groups based on the extent to which they were disturbed: scarcely, moderately, and intensively. Both the species richness and the diversity index were highest in the moderately disturbed group and lowest in the intensively disturbed group. These results indicate that the cessation of rice cultivation led to an overall simplification of the landscape elements and floristic composition of the valley ecosystern.