Chronological location analyses of giant bamboo (Phyllostachys pubescens) groves and their invasive expansion in a satoyama landscape area, western Japan

Since the 1980s, giant bamboo groves consisting mainly of naturalized Phyllostachys pubescens have been expanding in Japanese rural landscapes (satoyama). Using aerial photographs, I evaluated changes in bamboo grove distribution between 1947 and 2006 at Mount Hachiman, Ohmi-hachiman City in western Japan, where there is an area of satoyama landscape adjacent to the suburbs. I also quantitatively determined the natural and artificial factors that accelerated bamboo grove expansion using a multiple logistic regression analysis with stepwise procedure. I attempted to describe the positions of bamboo groves in Japanese satoyama landscapes. The area of bamboo groves in the survey area expanded after 1967. The bamboo groves are located at the base of mountain slopes and on alluvial fans adjacent to residential areas, where they are most susceptible to human interferences (mainly disturbance). They mark the boundary between agricultural fields and secondary forests. The model analysis indicated that the abandonment of lands adjacent to bamboo groves caused bamboo-grove expansion. As forests and agricultural land were abandoned, bamboo, mainly P. pubescens, invaded these areas by rhizomatous clonal growth. Bamboo grove expansion in Japanese satoyama landscapes is dependent on the type of land use, topography, and existing vegetation as well as the invasive life-history traits of P.pubescens.