南関東の 10 年後調査から見た在来 2 倍体種タンポポと外来種タンポポの出現状況変化

概要

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A follow-up survey of dandelion plants (Taraxacum) in 1990-1992, ten years after the initial survey using the same site designation methods in the southern Kanto district, revealed the following facts. Firstly, in the Tokyo urban area, the occurrence of both dandelion species had little changed; that is, the introduced one dominated there. Secondly, in the suburban areas, the number of lots in the recent survey where the native diploid species dominated had decreased compared with the previous survey, whereas the number of lots where the introduced species dominated had increased. Third, analysis of land-use in the two surveys revealed that a sharp decrease in cultivated fields, which are preferred by the native diploid species, caused a 48.7% drop in this dandelion's occurrence in the suburban areas. The count of the introduced dandelions also dropped by 3.5% in southern Tama, one suburb area. This species decreased in sites such as roadsides and vacant areas that have diminished, and increased on areas such as parking lots and children's playgrounds that have been expanded over the last ten years. These findings clarified the fact that decreases in habitat resulted in the retreat of ranges and declines in the frequency of occurrence for both dandelion species in the urban and suburban areas.
2001-02-28