Riparian landscape changes over a period of 46 years, on the Azusa River in Central Japan

Change in a riparian landscape was studied for the Azusa River of Central Japan, where Chosenia arbutifolia A. Skav. and Robinia pseudo-acacia L. grow. The objectives were: 1) to describe the dynamics of plant communities over a 46-year period (1948–1994) by using air photographs; and 2) to evaluate the effects of C. arbutifolia and R. pseudo-acacia on riparian landscape diversity. Both species could colonize throughout the study period because their ecological niches differ, i.e. C. arbutifolia grows mainly on the islands and terraces along streams newly formed by channel-changing, whereas R. pseudo-acacia establishes itself primarily on the terraces supporting the revetment. After R. pseudo-acacia scrubs established near the revetment, they invaded the land which different vegetation types, such as native Salicaceous and Pinus densiflora forests, already occupied. In particular, the stability of beaches promoted the succession of beaches in various forest types during the period 1975–1989 and contributed to the increase in riparian landscape diversity. The rapid increase and wide ecological niche of R. pseudo-acacia patches, however, may bring about a decline in the landscape diversity and biodiversity in the near future.