Broadleaved forests

Coastal formations are subject to special ecological conditions, which give them a very specific appearance, although they are today found only as scattered remnants, most of them having suffered extensive human interference (plantations, grazing, food crops, etc.). Four coastal formations can be distinguished according to the island group on which they are found:

    Hibiscus-Acrostichum swamp forest is found in the Society Islands (Tahiti and Moorea) in marshy zones with salt water. This is a closed formation, reaching a height of 6 to 8 m; Hibiscus tiliaceus predominates, accompanied by Thespesia populnea or Terminalia catappa; the herbaceous cover is patchy, and is composed of Acrostichum aureum, a typical fern here;
    Hernandia-Thespesia forest is also found in the Society Islands (Tahiti and Moorea) on volcanic or coral sands. It grows to 10 or 15 m, and its upper storey includes Thespesia populnea, Hernandia sonora and Cordia subcordata; the undergrowth is shrubby, and the herbaceous cover patchy;
    Guettarda-Hernandia forest is found on Makatea (Tuamotu Islands), reaching a height of 6 to 8 m. The most plentiful species are Guettarda speciosa and Pandanus tectorius, which are accompanied by Hernandia sonora, Thespesia populnea, etc.;
    Thespesia-Pisonia forest is a para-coastal formation on the Marquesas Islands (Nuku Hiva) up to an altitude of 300 m. It survives only in a residual form, reaching a height of 15 m. The dominant species is Pisonia grandis, which is found in association with Calophyllum inophyllum and Perminalia glabrata; the undergrowth is open.
    Forests on atoll and motu plateaux (particularly on Makatea in the Tuamotu Islands) take two main forms:
      Guettarda-Pandanus forest encircles the Makatea plateau and is also found on the motus in the Tubuai Islands at altitudes up to 100 m. This is a low forest, 4 to 6 m in height, dominated by Guettarda speciosa and Pandanus tectorius; the undergrowth contains lianas and epiphytes; Homalium-Planchonella forest is found in the central depression of Makatea. It grows to heights of over 20 m, with Homalium mouo and Planchonella taitensis as the dominant species; the undergrowth is very varied, with palms (Pritchardia vuylstekeana), Ixora triflora, Myrsine collina, etc. One of its degraded forms is a Tecoma-Epipremnum forest containing many naturalized species. null

      Moisture-loving formations in low- and medium-altitude valleys (900 m maximum) occur in river beds and the lower and middle parts of valleys, and require heavy rainfall (roughly 3 000 mm/year). They contain such indigenous forest species as Hibiscus tiliaceus and Neonauclea forsteri, but also such exotic species as Aleurites proluccane and Inocarpus fagifer. There are four types of formation, depending on the island in question:

        Hibiscus-Etlingera forest is found at up to 200 m on some islands in the Society group. Its canopy is about 12 m high, with Hibiscus tiliaceus as the dominant species, accompanied by Inocarpus fagifer; Etlingera cevuga and Zinziber zerumbet also cover large areas along mean-water beds. The undergrowth contains indigenous shrubs, and the herbaceous cover is varied, including many ferns;

        Neonauclea-Angiopteris forest is found at up to 900 m, covering large areas adjacent to the Hibiscus-Etlingera formation; it is a closed, tall (15-20 m) formation dominated by Neonauclea forsteri and Rhus taitensis. The shrubby undergrowth contains many endemic species (Claoxylon taitense, Cyrtandra spp., etc.). The herbaceous cover includes ground ferns and epiphytes, but the most distinctive species is Angiopteris evecta, a large bulbous rhizome with foliage over 4 m tall;

        Hibiscus-Angiopteris forest is found on Rurutu (Tubuai Islands) and Nuku Hiva (Marquesas Islands), but with slight differences. This is a low (10 m) riparian forest with a poorer flora than the preceding formation; apart from the two main species, it also contains Cerbera manghas and Glochidion raivavense. This type of formation has a shrub storey (Alyxia stellata, Macropiper latifolium), and a herbaceous layer containing many ferns. In zones that have been subject to extensive human intervention, a formation of Mangifera and Coffea, two exotic and recently naturalized species, is found;

        Hibiscus-Pandanus-Weinmannia forest is found on the Marquesas Islands. It is a transitional stage between Hibiscus-Angiopteris forest and higher-altitude forest (see below). Some species from moisture-loving formations are found together with higher-altitude forest species, including Weinmannia parviflora, Crossostylis biflora and many epiphytes and ground ferns.

        Mesophile formations on low- and medium-altitude hills are the most extensive up to 400 or 600 m, but also the most degraded. They are found in regions where the annual rainfall is under 3 000 mm, and include such species as Metrosidereos collina, Commersonia bartramia and Xylosma suaveolens. Degraded forms are mainly the result of fires. These formations can be divided into three types:

          Metrosideros-Commersonia forestis found on the crests and plateaux of some of the Society Islands. It is a low forest (5-7 m) made up mainly of Metrosideros collina, Commersonia bartramia and Xylosma suaveolens;

          Sapindus-Xylosma forest is found on the Marquesas Islands (mainly Nuku Hiva) as scattered remnants, up to 500 m. Sapindus saponaria and Xylosma suaveolens are accompanied by many naturalized species. When degraded, it becomes shrubby (see below), with Leucaena bushland and Dicranopteris heath;

          degraded forms include the Hibiscus-Mangifera forest found between 20 and 400 m in the Society Islands. Floristic variety is a significant feature, with indigenous species (Hibiscus tiliaceus and Pandanus tectorius) being found together with introduced ones (Mangifera indica and others); the undergrowth also contains a mixture of indigenous and introduced species.

        Medium- and high-altitude rainforest, found between 600 and 1 500 m, requires heavy rainfall (over 3 000 mm/year) and high air humidity from a permanent cloud cover. These are forests of Metrosideros, Weinmannia and Alstonia, but Freycinetia and Pandanus are also common:

          Weinmannia-Alstonia forest (Society Islands) is a low formation (7-10 m) and is composed mainly of Weinmannia parviflora, Alstonia costata and a tree fern, Cyathea affinis. Shrubs are all endemic, and the herbaceous layer is rich, with ferns predominating;

          Ilex-Streblus forest (Society Islands) is the best preserved woody formation in the Society Islands. Normally reaching a height of 5 to 8 m, it can reach 15 m in the most favourable places (high valley slopes). It is a wet forest and has a high rate of endemism, with Ilex taitensis and Weinmannia parviflora as the dominant species on the crests; Alstonia constata is also present on slopes, but the floristic composition varies with local conditions. Ground ferns, epiphytes, mosses and lichens are remarkably abundant;

          Metrosideros-Cyathea forest (Tubuai Islands) is found in ravines. It is distinguished by the presence of Cyathea medullaris, in association with Metrosideros collina, but also contains endemic shrubs and ground ferns or epiphytes;

          Hernandia-Cyathea forest (Marquesas Islands), lying between altitudes of 800 and 1 000 m, is made up of Cyathea affinis, Weinmannia parviflora, Fagrea berteroana and Hernandia nukuhivensis, reaching a height of 15 m; the undergrowth contains many endemic species;

          Ilex-Cheirodendron forest (Marquesas Islands) is a low (3-5 m) closed formation composed mainly of Ilex marquesensis and Cheirodendron bastardianum, as well as many endemic woody species (Coprosma spp., Psychotria spp., etc.).

last updated: Monday, January 12, 2004