Phytosociological study of semi-natural grasslands in the Ryukyu Islands

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  • YAMATO Michiko
    Center for Water Environment Studies, Ibaraki University
  • ASAMI Kayo
    Institute of Rural & Urban Ecology Co., Ltd.
  • TAKEDA Yoshiaki
    Division of Science for Biology and Environment, Faculty of Human Development, Kobe University

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Other Title
  • 琉球列島における半自然草原の植物社会学的研究

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Abstract

Semi-natural grasslands in the Ryukyu Islands were re-examined phytosociologically. As a result, four associations were classified: Thelyptero-Miscanthetum sinensis, Paspalo-Imperatetum cylindricae, Bidenti minoris-Imperatetum cylindricae and Euphorbio-Zoysietum tenuifoliae. These associations were contained in three alliances: Lygodio-Miscanthion sinensis, Imperation cylindricae and Zoysion tenuifoliae. Bidenti minoris-Imperatetum cylindricae is a new association differentiated by the presence of Bidens pilosa var. minor, Polygala paniculata, Centaurium floribundum, etc. This association develops at construction sites subject to weeding in urban areas such as slopes alongside expressways, open space of airfields, etc., and it is characterized by high ratios of therophytes, naturalized plants, species belonging to Artemisietea principis and Chenopodietea, and low ratios of hemicryptophytes and species belonging to Miscanthetea sinensis. These ecological characteristics are similar to those of Erigeronto-Imperatetum cylindricae which is maintained at construction sites subject to weeding from Tohoku to Kyushu district. Bidenti minoris-Imperatetum cylindricae seems to be an association in the Ryukyu Islands which corresponds to Erigeronto-Imperatetum cylindricae. Thelyptero-Miscanthetum sinensis was divided into two lower units dependent on the management. The Typical lower unit under abandonment of management is taller in vegetation height and lower in species richness than the Dianella ensifolia lower unit under traditional management. It was clarified that recent changes of environmental conditions in the Ryukyu Islands, such as weeding at construction sites, abandonment of management on traditional grassland communities, etc., have led to the appearance of a new association as well as simplification of the floristic composition. Furthermore, traditional semi-natural grasslands are rapidly decreasing in area due not only to the abandonment of management but also to grassland improvement, etc. From the standpoint of conservation of biodiversity, it was indicated that more detailed studies of actual conditions and conservation measures are immediately necessary in semi-natural grasslands of the Ryukyu Islands.

Journal

  • Vegetation Science

    Vegetation Science 21 (1), 1-13, 2004

    The Society of Vegetation Science

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