Polynesian Lowland Rain Forest

Human habitations or agricultural crops such as coconut groves, banana patches or breadfruit trees, have largely replaced most of these forests. However, a few valley forests exist. On Moorea (Society Islands) they are dominated by Inocarpus (mape) trees, which typically have large fluted trunks and intricate buttresses. Hibiscus tiliaceus is also an important component, and in less disturbed areas there are understory shrubs comprising Canthium barbatum and the endemic Ixora mooreaensis (Rubiaceae). There is a rich terrestrial and epiphytic flora with many ferns. The largest of these is the curious Angiopteris erecta, which has a huge barrel-like, erect rhizomes or corms covered in fleshy stipules and giant fronds reaching 4.5 m in length. On the valley sides there are dense tangled shrubs of Aleurites moluccana, Hibiscus tiliaceus and the endemic Rhus taitensis (Anacardiaceae). Other indigenous species on these slopes include the remarkable but rare endemic Lepinia taitensis (Apocynaceae) with it large, hanging, basket-like fruits. Inocarpus-Hibiscus forest is also characteristic of the valleys on Huahina (Society Islands), but just above this zone are stands of huge pandans together with indigenous trees such as Crossostylis biflora, Neonauclea forsteri and the endemic Xylosma suaveolens (Salicaceae).  

 

Polynesian Montane Rain Forest

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 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.

 

Polynesian (Makatea) Vegetation

This is named after Makatea Island (northern Tuamotus) and refers to the vegetation of rugged limestone of elevated atolls. There are usually concentric rings of coastal makatea with the vegetation becoming richer away from the coast. It can also be found on Atiu, Mangaia, Ma’uke and Mitiàro (Cook Islands) and the Plateau of Henderson Island (southern Tuamotus). Here it consists of a low tangle of shrubs dominated by Timonius polygamus. Other shrubs include dwarf versions of Cassytha filiformis, Cyclophyllum barbatum, Phymatosorus scolopendria, Pisonia grandis and the endemic Santalum insulare var. hendersonense (Santalaceae). In this rugged landscape some of the fissures are up to 1.5 m deep and may contain the endemic Peperomia hendersonensis (Piperaceae) and ferns such as Nephrolepis hirsutala.

 

Polynesian (Easter Island) Grassland

Grasslands now cover much of the lava plains and slopes and crater depressions on this island. Early inhabitants probably removed any forest cover, but there is no evidence to suggest that the island was ever heavily forested. The original vegetation was probably a type of savanna but with plenty of the endemic but now extinct tree Sophora toromiro (Fabaceae). There is sufficient rainfall to permit tree growth but the island’s rocks and soil are very porous and as a result there are no streams on the island. This is exacerbated by the frequent desiccating winds. In fact, several of the indigenous grasses have xeromorphic features. Nevertheless, the term ‘tropical oceanic’ has been used to describe these grasslands. The dominant grasses are Agrostis retrofracta, Dichelachne sciurea, Eragrostis elongata, Sporobolus elongatus and the endemic Axonopus paschalis, Dantonia paschalis and Stipa horridula (Poaceae). On the lava flows and slopes other characteristic species include the sedge Killinga brevifolia and the ferns Microlepia strigosa, Ophioglossum coriaceum and O. reticulata, while in moist fissures other ferns such as Aspenium obtusatum, Doodia paschalis and Polypodium phymatatodes occur. This is also the habitat of the rare Nasturtum sarmentisum.

 

Polynesian (Easter Island) Scrub and Fern Fields

On the talus slopes of the islands craters carpets of ferns, mainly Microlepia strigosa, but also including Dryopteris gongylodes, D. parasitica and Polypodium phymatodes occur together with luxuriant moss mats. These are accompanied by a scattering of trees and shrubs, which prior to about 1920 included Broussonetia papyrifera, Triumfettia semitriloba and the endemic Sophora toromira (Fabaceae), but the latter species now appears to be extinct. With just eleven vascular plants and a variety of mosses and lichens this is considered to be the richest vegetation on the island.

Further information required.

 

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