Coastal vegetation of small islands near Viti Levu and Ovalau, Fiji

Vegetation studies of nine small islands off the east and south-east coasts of Viti Levu show that, for most islands, species richness is low and represents between 21% and 44% of the total recorded species for the islands. The majority of species on each island are dispersed by sea (oceanic currents) or by animals (birds and bats). Wind dispersed species are few on all islands. Fifteen species are common to five islands and four and six species are common to all nine and eight islands, respectively. The number of native species on each island is variable and ranges from 65% to over 90%. Weedy species are mainly associated with cultivation and plantations. Two major vegetation types are distinguished: the reef flat mangrove, and the sandy beach vegetation. Both vegetation types show a pattern of zonation of species from the beach inland. The vegetation of small sandy islands (up to 30 ha) that are relatively undisturbed consists mainly of coastal herbs, shrubs, and trees. TWINSPAN classification showed that islands with similar topography and substrate have similar plant communities. Our limited data suggest that small sandy islands that lack inland topographical features (such as hills) show an increase in species richness with an increase in island area. However, since full floral surveys were not carried out for all islands, this correlation may not stand true for the larger islands or for islands with inland topographical features. We suggest that the major factors responsible for the low species richness of small islands are the chance arrival of water and/or bird dispersed seeds and a suitable habitat (substrate) for the successful establishment of the species.