Included here is Cook Island of Tahiti, the Line Islands, Marguesas Islands, Mangarera Islands, Society Islands, Tubuai Islands, Tuamotus Islands (such as Pitcairn and Henderson Islands), Ducie Island, Easter Island, Rapa Island and Sala-Y-Gomez.

Polynesian Montane Rainforest

These forests are widespread on windward slopes usually starting at an altitude of about 500 m. On Rarotonga (Cook Islands) they can be broadly divided into forests dominated either by the endemic Homalium acuminatum (Salicaceae) or by the co-dominance of the two endemics Fagraea berteroana (Loganiaceae) and Fitchia speciosa (Asteraceae). The former is a closed-canopy forest of inland mountain slopes and commonly includes other tree species such as Canthium barbatum, Elaeocarpus tonganus and Ixora bracteata, while less common trees are Bischofia javanica, Macaranga harveyana, Pouteria grayana and the endemic Terminalia glabrata (Combretaceae). Forests dominated by Fagraea and Fitchia are mainly confined to steep ridges at middle elevations. Both dominant species have extensive root systems that help stabilize the loose rocks and soil of narrow ridge tops. Ridge forests can also be found, for example, on Raiatea (Society Islands). Here they are characterised by Alphitonia zizyphoides, Canthium barbatum, Cerbera manghas, Decaspermum fruticosum, Hernandia moerenhoutiana, Melastoma denticulatum and the endemic Alstonia costata (Apocynaceae). All of these forests support many epiphytes and vines. On Raiatea, for example, the vines include Merremia peltata and the viny ferns Dicranopteris linearis and Lygodium reticulatum.

Polynesian Montane Cloud Forest

At high elevations on many Polynesian islands there is almost continuous cloud cover or fog producing the highly humid conditions necessary for the development of these forests. In the Cook Islands it is confined to the largest island Rarotonga and even here it is restricted to relatively small areas of interior mountain summits. The canopy is usually less than 8 m high and dominated by the endemic Metrosideros collina (Myrtaceae). Other associated woody species include the endemic Cyrtandra rarotongensis, C. lillianae (Gesneriaceae), Geniostoma rarotongensis (Loganiaceae) and Sclerotheca viridiflora (Campanulaceae). The trees are invariable festooned with epiphytic mosses and ferns, and the endemic liana Freycinetia arborea (Pandanaceae) is common. Other common indigenous species are Ascarina diffusa, Elaeocarpus tonganus, Elaphoglossum savaiiense, the endemic Vaccinium cereum (Ericaceae) and various tree ferns (Cyathea). In the Society Islands, Huahine, Mooorea, Raiatea and Tahiti all support cloud forest in their mountainous interiors. On Raiatea’s Temehani Plateau these dwarf forests are characterised by a variety of species including Descaspermum fruticosum and the two endemic trees Alstonia costata (Apocynaceae) and Metrosideros collina (Myrtaceae). Most of the woody species are no more than about 3 m high except for stands of the endemic Pandanus raiateensis (Pandanaeceae), which is usually less than 1 m. Other endemic taxa include the remarkable lebeloid Apetehia temehaniensis (family?) but it is becoming increasingly rare. Although the Marquesas Islands tend to be dryer than other Polynesian islands and have been ravaged by feral ungulates (goats) there are still remnant cloud forests on Fatu Hiva, Hiva Oa, Nuku Hiva and Tahuata. Here again the endemic Metrosideros collina is the dominant species.

Polynesian Limestone Plateau Forest

Forest covers much of the elevated limestone plateau of Henderson Island. In places it forms a closed-canopy dominated by Pisonia grandis, but with a wide range of associated species including the endemic Celtis pacifica (Ulmaceae), Glochidium pitcairnensis (family?) and Xylosma suaveolens (Salicaceae). However, many of the trees are partially decumbent and the canopy height is never more than about 10 m, but with occasional emergents like Guettarda speciosa and Pandanus tectorius. Lianas, including Morinda myrtifolia, are common and a rich shrub layer includes Cyclophyllum barbatum, Psydrax odorata and the endemic Ixora fragans (Rubiaceae). The herb layer is usually well developed and includes Asplenium nidus, Phymatosorus scolopendria, and the endemic Peperomia hendersonensis (Piperaceae). In fissured and pinnacled areas the endemic Hernandia stokesii (Hernandiaceae) becomes more conspicuous, while on the poorer soils the forest are more open. Here Xylosma suaveolens becomes co-dominant with Pisonia grandis and the endemic Bidens hendersonensis (Asteraceae) and Santalum insulare (Santalaceae) are more common. In places, such as around the plateau margins the forest gives way to thicket in which Cyclophyllum barbatum, Nephrolepis hirsutula, Psydrax odorata, Timonius polygamus and the endemic Geniostoma hendersonense (Loganiaceae) usually predominate.

References

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