LAND-USE SELECTION BY DANDELIONS IN THE TOKYO METROPOLITAN-AREA, JAPAN

Land use by native and introduced dandelion groups in man-made habitats was studied at 7090 survey points in the Tokyo metropolitan area, Japan, in order to clarify the replacement phenomenon occurring among dandelions. In the center of Tokyo, where the native group was rare, the percentage occurrence of the introduced group was lower than in other regions, whereas in the outskirts of Tokyo, both groups showed much higher occurrence. Roadsides, vacant areas and urban land-use categories were significantly favorable for growth of the introduced group, whereas preserved or rural land use was more favorable for the native group. Seed fertility in the introduced group was more than 80%, and was independent of population size, whereas in the native group it was not as high, and for a small population was dependent on population size, being stable at about 70% in populations larger than 70 plants. Thus, both large populations and solitary plants in the introduced group appeared to act as seed sources, making it likely that the introduced group will spread increasingly through roadsides and urban land, which are becoming more widespread as a result of urbanization. It is feared that, unless deliberately retained, the amount of preserved or rural land which has fostered large populations of the native group will further decrease with urbanization and other forms of development, thus depleting the seed sources and reducing the population.