The authors tried a phytosociological vegetation survey as a fundamental part of landscape evaluation and planning in the humid sub-tropical Izena Island located in the northern part of Okinawa, southwest Japan. It is the purpose of this paper to clarify the geographical distributions and the characters of plant communities, which are affected not only by the land potentiality but also by a lot of human interventions in the Izena Island.
As a result of plot survey, forest and weed vegetation of the Izena Island has been divided into 9 plant communities, and 2 plant communities further Into 4 and 2 subordinate communities. That is ;
1. Forest vegetation,
A. Pandanus tectorius community,
B. Thuarea involuta-Casuarina equisetifolia community,
C. Leucaena leucocephala community,
D. Pinus luchuensis community, a. subordinate comm. of Aristida takeoi, b. subordinate comm. of Rhodomyrtus tomentosa, c. subordinate comm. of Castanopsis sieboldii, d. typical subordinate comm.,
E. Pittosporo-Quercetum phillyraeoidetis Suz.-TOK. et HATIYA 1951,
a subass. of Pinus luchuensis, b. subass. of Fraxinus insularis,
F. Ardisia sieboldii-Cinnamomum japonicum community
2. Weed vegetation
G. Marsilea crenata-Scirpus maritimus community,
H. Typha domingensis community,
I. Oxalis corniculata-Panicum repens community,
Under the recognition of the spatial distributions of the differential species in the communities, actual vegetation map was drawn up as Fig. 3.
Then the authors discussed on the relationship between land potentiality, especially soil potentiality, and plant communities by using vegetation map. They also discussed on the relationship between land use, including religious preservation of special areas in the Izena Island, and plant communities. They found the distributions of plant communities in the Izena Island to be characterized not only by the influences of land conditions such as soil pH but also by the great influences of human interventions such as agricultural land-use.
Such discussions will be useful when we consider the fundamental character of the landscape complex in the humid sub-tropical islands of Japan.

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