Abstract
Since it was introduced to Japan, the black locust (Robinia pseudoacacia L.) has been used for controlling erosion and restoring copper mine and coastal forests. Recently, it has spread to river basins throughout Japan, threatening river ecosystems. The unique life history of the black locust can explain its spread. It has both dormant and non-dormant seed types, which can germinate immediately after dispersal. Seeds produced up-stream were found to be carried downstream by water flow, and seed germination often occurred on new fine deposits after flooding. Black locust trees initially grow very quickly, but only bloom some years later. This early growth is dependent on a high photosynthetic rate under optimal conditions. Many root suckers emerge from horizontal roots, extending away from the mother tree and eventually expanding into new patches. Thus, this alien species has expanded its range downstream due to its unique life-history strategy.
