Broadleaved forests

Littoral Forest

Growing on sandy or rocky substrates in a narrow zone, littoral forest occurs between low- strand 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. Rose Atoll supports a Pisonia forest. 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. Casuarina equisetifolia has not naturalized in American Samoa (or Samoa).

In some areas seaward of the littoral forest, mono-dominant thickets of Pandanus tectorius 1 to 6 m high can be found (e.g., east coast of Ta'u; Swains Island).

On Swains Island, only scattered patches of littoral forest remain, dominated by Hernandia nymphaeifolia or Pandanus. Other tree genera include Guettarda, Neisosperma, Pisonia and Tournefortia.

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 are often flooded by fresh water. The closed canopy allows only Bruguiera seedlings in the understory, but the swamp fern Acrostichum aureum and trees of the species Rhizophora samoensis occupy openings.

Often fronting mangrove forest is a mangrove scrub community dominated by small to medium-sized trees of Rhizophora samoensis. Where Rhizophora competes with the larger Bruguiera gymnorrhiza, the former is shaded out. Mangrove scrub is found, particularly, on the south-central coast of Tutuila.

null

Lowland Rain Forest

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

  • 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. An example of this forest can be foundon Nu'utele Islet off 'Ofu.
  • Dysoxylum Forest: A low-statured forest dominated by Dysoxylum mollissimum ssp. molle along with D. gaudichaudianum, this forest type can typically be found in alluvial valleys, on steep lowland cliffs, and on talus slopes (e.g., northern coast of Tutuila, east coast of Ta'u). Other canopy trees include Barringtonia samoensis, Bischofia javanica, Cananga odorata, Elaeocarpus ulianus, Ficus scabra, Kleinhovia hospita, Macaranga stipulosa, Myristica fatua, Neonauclea forsteri and Terminalia richii.
  • 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.

Montane Rain Forest

Above 500 m elevation conditions become wetter (5 000 mm rainfall at 600 m elevation), thedrier lowland rain forest gives way to a montane forest dominated by Dysoxylum huntii. Two other species of Dysoxylum (D. gaudichaudianum, D. mollissimum ssp. 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