Included here is Christmas Island some 300 km south of Java in the Indian Ocean. On the plateaus and terraces, what appears to be typical evergreen forest occurs with emergent tree up to 45 m. It has a mixture of Indo-Malaysian and Melanesian elements. However, this forest is unique in that the composition and recruitment of plant species is largely controlled by huge numbers of the endemic terrestrial crab Gecarcoidea natalis. The forest floor is almost devoid of leaf litter, seeds and seedlings, since the crabs quickly consume them. It is estimated that there are approximately 100 million of these crabs in the forest. The upper canopy trees comprise Barringtonia recemosa, Cryptocarya nitens, Dysoxylum gaudichaudianum, Inocarpus fagifer and Tristiropsis acutungula, while the typical emergents are Ficus macrocarpa, Hernandia ovigera, Planchonella nitida and Syzygium nervosum. The under storey includes Leea angulata, Ochrosia ackeringae, Pisonia umbellifera and the Christmas Island endemics Arenga listeri (Arecaceae) and Pandanus elatus (Pandanaceae). Shrub layer species include the Christmas Island endemics: Abutilon listeri (Malvaceae), Colubrina pedunculata (Rhamnaceae), Grewia insularis (Tiliaceae) and Pandanus christmatensis (Pandanaceae), and there are various vines like the Christmas Island endemics: Hoya aldrichii (Apocynaceae) and Zehneria alba (Acanthaceae). Other Christmas Island endemics include the fern Asplenium listeri (Aspleniaceae), the orchids Brachypeza archytes, Flickeringa nativitatis, Phreatia listeri (Orchidaceae), other herbs such as Asystasia alba (Acanthaceae), Dicliptera maclearii (Orobanchaceae), Peperomia rossii (Piperaceae), and the grass Ischaemum nativitatis (Poaceae). However, on the more shallow soils of coastal terraces prone to dehydration these evergreen forests give way to a semi-deciduous forest. Here the typical species are Acronychia trifoliolata, Berrya cordifolia, Calophyllum inophyllum, Erythrina variegata, Gyrocarpus americanus, Hibiscus tiliaceus, Kleinhovia hospita, Ochrosia ackeringae, Pisonia grandis, Terminalia catappa and the endemic Pandanus elatus (Pandanaceae).

References

Green, P. T. 1997. Red crabs in rain forest on Christmas Island, Indian Ocean: activity patterns, density and biomass. Journal of Tropical Ecology, 13: 17-38.

Leith, H. & Werger, M. J. A. 1989. Ecosystems of the World 14B - Tropical Rain Forests. Elsevier Scientific Publishing Company.