Plant Formations in the Vanuatu BioProvince

Peter Martin Rhind

Vanuatu Mixed Lowland Rain Forest Up to about 600 m altitude lowland rain forest is the natural vegetation on the southeastern, windward sides of all Vanuatu islands. Important trees are Antiaris toxicaria, Castanospermum australe, Intsia bijuga and Kleinhovia hospitat. Endemic species include Alangium vitense (Cornaceae). On old volcanic ash, rich in plant nutrients, trees can reach more than 30 m in height with large crowns. Typical sub canopy trees include Diospyros acris, Garcinia pancheri and Syzygium species, while endemic small trees include various Veitchia palms, Calophyllum inophyllum (Clusiaceae) and Trilocularia pedicellata (Balanopsidaceae). These forests are best developed on the northern islands of Malakula and Espiritu Santo, and are structurally similar to forests on the Solomon Islands. However, many are in various stages of recovery following disturbance from hurricanes. Vines and epiphytes are numerous and certain areas are covered with lianas. The undergrowth includes various shrubs, and typically there is an herbaceous ground layer comprising genera such as Geophila and Homalomena and ferns like Asplenium, Microsorium and Pteris, but tree ferns are usually absent. Of endemic species, however, many seem to be specific to certain islands or island groups. On Aneityum, for example, there are endemic trees such as Boehmeria anisoneura (Urticaceae), Canarium aneityensis (Burseraceae), Couthovia neo-ebudica (Loganiaceae), Cryptocarya wilsonii (Lauraceae), Cupaniopsis aneityensis (Sapindaceae), Decaspermum neo-ebudicum (Myrtaceae), Dedea neo-ebudica (Saxifragaceae), Dolicholobium aneityense (Rubiaceae), Elaeodendron artense (Celastraceae), Endiandra aneityensis (Lauraceae), Ficus acrorrhyncha (Moraceae), Geissois denhamii (Saxifragaceae), Grewia inmac (Tiliaceae), Guettarda kajewskii (Rubiaceae), Hedycaria neo-ebudica (Monimiaceae), Homalium aneityense (Samydaceae), Ixora aneityensis (Rubiaceae), Kermadecia lutea (Proteaceae), Leucosyke corymbulosa (Urticaceae), Ligustrum beo-ebudicum (Oleaceae), Litsia aneityensis (Lauraceae), Melia azedarach (Meliaceae), Myrtus aneityensis (Myrtaceae), Palaquium neo-ebudicum (Sapotaceae), Pittosporum aneityense (Pittosporaceae), Sideroxylon aneityense (Sapotaceae), Semecarpus tannaensis (Anacardiaceae), Sideroxylon aneityense (Sapotaceae), Syzygium aneityensis (Myrtaceae), Tieghemopanax neo-ebudarum (Araliaceae), Weinmannia macgillivrayi (Cunoniaceae), and the palm Kajewskia aneityensis (Arecaceae). Endemic shrubs in these rain forests include Cyrtandra aneiteensis (Gesneraceae), Elatostema macrophyllum (Urticaceae) and Psychotria aneityensis (Rubiaceae), while other endemics include epiphytes such as the orchid Eria kajewskii (Orchidaceae), the vine Faradaya neo-ebudica (Lamiaceae), and the parasites Loranthus aneityensis (Loranthaceae) and Medinilla neo-ebudica (Melastomaceae).

Vanuatu Agathis-Calophyllum Forest Forest dominated by the endemic Agathis obtusa (Araucariaceae)) and Calophyllum neo- ebudicum (Clusiaceae) are confined to the southern islands of Anatom and Erromango, although scattered emergent kauri (Agathis spp) have been reported as occurring in the western mountains of Espiritu Santo, but no Calophyllum. Agathis and species of Podocarpaceae form an ancient floristic element of these forests. The fossil record of Agathis, for example, can be traced back to the Jurassic period and extant species often referred to as ‘living fossils’. In the Jurassic the now extinct Agathis jurassica was widespread, but today the genus is confined to Malaysia, Brunei and Indonesia, New Guinea, Queensland and the eastern Solomons to Vanuatu, New Caledonia, Fiji and New Zealand. Other common trees found in these forests include Acronychia simplicifolis, Copyright © 2010 Peter Martin Rhind Bleasdalia lutea, Canthium cynigerum, Celtis paniculata, Dacrycarpus imbricatus, and the endemic Dysoxylum aneityensis (Meliaceae), Elaeocarpus hortensis (Elaeocarpaceae), Ficus granatus (Moraceae) and Palaquium neo-ebudicum (Sapotaceae). The canopy can reach heights of up to 30 m with emergent Agathis occasionally reaching 35 m. Subcanopy genera include Cryptocarya, Dysoxylum, Ilex, Litsea, Piliocalyx, Polyscias, Schefflera, Syzygium, Weinmannia and others, and there is usually a tall shrub stratum consisting of genera such as Dracaena, Ilex, Myristica and Syzygium. Other endemic trees associated with these forests on Erromango include Aphania neo-ebudica (Sapindaceae), Badusa occidentalis (Rubiaceae), Cupaniopsis neo-ebudensis (Sapindaceae), Dillenia neo-ebudica (Dilleniaceae), Eugenia richii (Myrtaceae), Evodia kayewskii (Rubiaceae), Ficus kajewskii (Moraceae), Homalanthus longipes (Euphorbiaceae), Tapeinopserma netor and Weinmannia kajewskii (Saxifragaceae). There is typically a rich herb layer usually dominated by ferns. Ferns are also well represented among the epiphytes together with orchids, particularly species of Dendrobium. Lianas include Alyxia, Entada, Freycinetia and Hugonia and included among the many vines are the endemic Parsonsia neo-ebudica (Apocynaceae) and Uncaria orientalis (Rubiaceae).

Vanuatu Montane Cloud Forest These forests range from about 500-1000 m in altitude and so confined to the highest mountains in Vanuatu such as the southeast slopes of Pico Santo (1704 m) and the eastern side of Tabwemasana (1879 m). On smaller islands such as Anatom they develop at about 300 m. They are all characterized by stunted, gnarled trees covered in bryophytes and filmy ferns. The main tree genera are Ascarina, Geissois, Metrosideros, Quintinia, Syzygium and Weinmannia. Also tree ferns of Cyathea and Dicksonia are locally common together with various other large ferns. The endemic palm Clinostigma harlandii (Arecaceae) may also be present but appears to be confined to the islands of Ambrym, Anatom and Erromango. Many of the tree crowns are covered with epiphytic orchids, particularly species of Dendrobium, and ferns. Astelia (Liliaceae) is another conspicuous epiphyte. Lianas, on the other hand, are less numerous but include the pandanaceous climber Freycinetia. Scattered among the trees are various herbaceous patches with plants such as large leaved Gunnera, the grass Isachne and the sedge Machaerina. Shrubs such as Eurya, Gaultheria, Pipturus and Vaccinium can also be found in these treeless, herbaceous zones.

Vanuatu Acacia spirorbis Forest Know locally as gaiac forest this open formation dominated by the phyllodial Acacia spirorbis can be found on various islands including Anatom and Erromango. The trees usually have a low to medium stature growing to a maximum of about 15 m, and typically have wide-branching crowns. Dominant among undergrowth shrubs are Croton, Symplocos and Xylosma. In canopy openings, heliophytic grasses predominate. These include Miscanthus floridulus in moist areas and Heteropogon contortus in the dryer areas.

Vanuatu Vegetation of New Volcanic Surfaces On Yasur Volcano on Tanna, the ferns Histiopteris incisa, Nephrolepis hirsutula and Cyathea species are widely but sparsely distributed on lava fields, but a completely different flora occurs on the disturbed cinder cones. Here the dominant species include shrubs such as Melastoma denticulatum, Piper latifolium and Pipturus argenteus, the grasses Imperata cylindrical and Miscanthus floridulus, and the annual herb Emilia sochifolia. Surprisingly orchids have also been recorded in these inhospitable areas including species of Spathoglottis, while on the volcanic ash of Erromango the endemic orchid Trichochilus neo-ebudidus (Orchidaceae) can be found.

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Copyright © 2010 Peter Martin Rhind