Broadleaved forests

Littoral Forest

This forest type grows on sandy or rocky substrates in the narrow zone between low-growing littoral vegetation on the seaward side and lowland forest inland. The most extensive of the littoral communities, it is often dominated by a single tree species, especially Barringtonia asiatica, Calophyllum inophyllum, Hernandia nymphaeifolia, Pisonia grandis or Terminalia catappa. Other characteristic trees include Cerbera manghas, Cocos nucifera, Cordia subcordata, Guettarda speciosa, Neisosperma oppositifolia, Thespesia populnea and Tournefortia argentea. The forest floor is only sparsely covered. Curiously, Casuarina equisetifolia is not naturalized in Samoa (or American Samoa).

In some areas just seaward of the littoral forest, mono-dominant thickets of Pandanus tectorius 1 to 6 m high can be found (e.g., cliffed coasts of Savai´i and ´Upolu).

Mangrove Scrub and Forest

Mangrove forests dominated by stands of Bruguiera gymnorrhiza typically occur in protected coastal bays and estuaries where fresh water enters the ocean. These habitats are inundated by saline or brackish water at high tide and often flooded by fresh water. The closed canopy allows only Bruguiera seedlings in the understory, but the swamp fern Acrostichum aureum and Rhizophora samoensis occupy openings. In one locality on the southern coast of Savai´i, Xylocarpus moluccensis, rare in Samoa, is associated with Bruguiera.

Often fronting mangrove forest is a mangrove scrub community dominated by small to medium-sized trees of Rhizophora samoensis. Where Rhizophora samoensis competes with the larger Bruguiera gymnorrhiza, the former is shaded out by the latter. Mangrove scrub can be seen in the ´Apia area of ´Upolu.

Swamp Forest

These forests are unified by their substrate of freshwater-saturated soil. In Western Samoa these occur in coastal and inland habitats. One coastal example along the south side of ´Upolu is dominated by Inocarpus fagifer; another on the west side reportedly includes scattered trees of Erythrina fusca. Inland basins and craters with poor drainage also provide swamp forest habitat. The crater at Fogalepolo in eastern ´Upolu contains a swamp, the central part dominated by Pandanus tectorius, with an outer margin of Barringtonia samoensis. Other large tracts of swamp forest on eastern ´Upolu contain a mix of species but have not yet been studied.

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Lowland Rain Forest

The most wide-ranging and complex forest type in Western Samoa, the following four lowland rain forest types are distinguished by their assemblage of species and by substrate and moisture characters.

  • Diospyros Forest: A medium-statured forest on well-drained soil inland of littoral forest, this zone is dominated by Diospyros elliptica and D. samoensis in association with Syzygium clusiifolium and S. dealatum. Ficus obliqua is an important component, and littoral species such as Pisonia grandis are occasionally seen. Examples can be seen on the Aleipata Islands east of ´Upolu, and on Apolima Island between Savai´i and ´Upolu.

  • Pometia Forest: This forest is one of the tallest of Samoan rain forests, distinguished by its massive canopy emergents of Pometia pinnata; associated canopy elements include Dysoxylum mollissimum ssp. molle, Ficus prolixa, Myristica fatua, Neonauclea forsteri, and Planchonella samoense. It represents a mature Samoan rain forest on volcanically young soils. Once widespread in the lowlands of Savai´i and ´Upolu on rocky soils up to 450 m elevation, patches of Pometia forest can still be seen along their southern coasts.

  • Syzygium Forest: Representing a mature rain forest on ancient, deeply weathered volcanic soils, Syzygium forest can be found on lowland ridges and steep interior slopes. It is dominated by S. inophylloides; associated canopy trees include Alphitonia zizyphoides, Calophyllum neo-ebudicum, Canarium vitiense, Fagraea berteroana, Intsia bijuga, Myristica hypargyraea, Planchonella garberi and Syzygium samoense.

  • Planchonella Forest: Now of restricted distribution, this forest type represents a mature rain forest on moderately weathered volcanic soils. Dominated by Planchonella samoensis, associated trees include Calophyllum neo-ebudicum, Canarium vitiense, Dysoxylum gaudichaudianum, D.mollissimum spp. molle, Myristica fatua, and Syzygium inophylloides. Planchonella forest once formed much of the lowland cover on ´Upolu and significant areas on Savai'i.

Montane Rain Forest

Above 500 m elevation conditions become wetter (5 000 mm rainfall at 600 m elevation), and Planchonella forest gradually gives way to a montane forest dominated by Dysoxylum huntii. Two other species of Dysoxylum (D. gaudichaudianum, D. mollissimum spp. molle) common in the lowland forests thin out at these elevations. Associated canopy species include Astronidium spp., Bischofia javanica, Fagraea berteroana, Hernandia moerenhoutiana, Reynoldsia spp., Spiraeanthemum samoense, Syzygium spp., Trichospermum richii, and Weinmannia spp.

last updated: Monday, January 12, 2004