The Vanuatu rainforests consist of more than eighty true oceanic islands, in two groups, at the edge of both the Australasian realm and the Pacific Basin. They contain fifteen bird species and several mammal species found nowhere else in the world. Although it is faced with population pressures and regular visits by destructive cyclones, with few exceptions Vanuatu's natural heritage is nearly intact.
Location and General Description
This ecoregion consists of tropical lowland and montane forests in the island nation of Vanuatu (formerly New Hebrides), with the addition of the Santa Cruz Group, or Temotu Province of the Solomon Islands.
The climate of Vanuatu is tropical wet, although leeward slopes of islands experience a distinct dry season that may last from April to October. Destructive tropical cyclones are a regular event. The highest point in Vanuatu is 1879 meters (m) (Espiritu Santo Island), but most of the islands are low-lying. Vanuatu is the result of the subduction of the northward-moving Australian tectonic plate beneath the Pacific plate, and the islands are a very active tectonic area. Most of the surface geology of the islands consists of Pliocene-Pleistocene volcanic rocks and uplifted coral. The Santa Cruz Islands contain areas of uplifted limestone or volcanic ash over limestone. Very few rocks are older than 38 million years (m.y.), and the older material is found in the northern islands, with the exception of the Santa Cruz Islands, which are less than five million years old. There are active volcanoes in Vanuatu.
Geology and vegetation can be differentiated between the northern Santa Cruz Islands group and the rest of Vanuatu.
When not converted to agricultural use, the predominant vegetation type in the Santa Cruz Islands is lowland rain forest. The Santa Cruz Islands have two of the twelve common tree species found in the Solomons (Campnosperma brevipetiolata and Calophyllum vitiense). The islands differ phytogeographically from the rest of Vanuatu. Because the highest point on Vanikoro (in the Santa Cruz Islands) is only 924 m, there is no well-developed montane rain forest. However, some montane species, such as Metrosideros ornata, are found in the lowlands. Other prominent species include Gmelina solomoensis (Verbenaceae), Parinari corymbosa (Rosaceae), Paraserianthes (Albizia) falcataria, and Pterocarpus indicus (Fabaceae), and Endospermum medullosum (Euphorbiaceae). Agathis (kauri pine) is found in the Santa Cruz Islands, as are Dacrydium elatum and several Syzygium (Myrtaceae) species, which are generally montane species elsewhere.
Natural vegetation in the rest of Vanuatu changes with altitude, substrate, and aspect and can be broadly classified into lowland forest, montane forest, seasonal forest and scrub, vegetation on new volcanic surfaces, coastal vegetation, and secondary vegetation.
Lowland rain forest is the natural vegetation on all southeastern, or windward, sides of Vanuatu's islands, and it can be further subdivided into high and medium-stature forests, complex forest scrub densely covered with lianas, alluvial and flood plain forests, Agathis-Calophyllum forest, and mixed-species forests without gymnosperms and Calophyllum. The complex forest scrub densely covered with lianas is the most widespread forest type on the larger northern islands; it is related to cyclone disturbance and is structurally heterogeneous. Agathis-Calophyllum forest is found only in the southern islands (Erromango and Anatom), although scattered Agathis spp. are reported in western Espiritu Santo.
Montane forest types consisting of Agathis and Podocarpus-growing in a matrix of Metrosideros, Syzygium, Weinmannia, Geissois, Quintania, and Ascarina-begin at altitudes of approximately 500 m and grade into stunted, patchy cloud forest up to the summits of Vanuatu's mountain peaks.
Seasonal forest, scrub, and grassland are associated with the leeward sides of the islands and can be further subdivided based on a moisture gradient. Semideciduous Kleinhovia-Castanospermum forest contains some of the rain forest species and represents a transition from dry to rain forest. Acacia spirorbis (or gaiac, as it is locally known) forest is found in somewhat drier habitats. Finally, in well-sheltered locations on the west and northwest sides of the islands, Leucaena thickets, savannas, and grasslands are found. These areas are subject to burning by humans.
The coastal vegetation consists of both strand and mangroves. Tree species in the littoral forest include Casuarina equiseifolia, Pandanus, Barringtonia asiatica, Terminalia catappa, Henandia spp., and Thespesia populnea. The mangroves contain Rhizophora, Avicennia, Sonneratia, Xylocarpus, and Ceriops and are not found on all of the islands.
Such vegetation is typical of the main islands, but the outlying islands, including Torres Islands, Banks Islands, and Aoba, Ambrym, Epi, and the Shepards, have their own unique vegetations.
|Table 1. Endemic and Near-Endemic Mammal Species.|
|An asterisk signifies that the species' range is limited to this ecoregion.|
There is a clear gradient of the mammalian faunas from New Guinea, to the Bismarck Archipelago, through the Solomon Islands, to Vanuatu; areas of open ocean have acted as an effective filter. Except for pteropodid bats, the Solomons and Bismarcks (New Britain, New Ireland) have many fewer mammals than New Guinea. Unlike New Britain, the Solomons, contain no marsupials, and east beyond the Solomons there are even fewer mammal species. However, almost all mammal species in Vanuatu have their origins in or via New Guinea. The only mammals in Vanuatu are four pteropodid bats and eight microchiroptera. Six of these species are endemic or near endemic (Table 1). Of these endemic and near-endemic species, the Fijian blossom-bat (Notopteris macdonaldi) and Banks flying-fox (Pteropus fundatus) are considered vulnerable, and the Nendö tube-nosed bat (Nyctimene sanctacrucis) is presumed to be extinct.
|Table 2. Endemic and Near-Endemic Bird Species.|
|Megapodiidae||New Hebrides scrubfowl||Megapodius layardi*|
|Accipitridae||Pied goshawk||Accipiter albogularis|
|Columbidae||Santa Cruz ground-dove||Gallicolumba sanctaecrucis*|
|Columbidae||Tanna ground-dove||Gallicolumba ferruginea*|
|Columbidae||Tanna fruit-dove||Ptilinopus tannensis*|
|Columbidae||Baker's imperial-pigeon||Ducula bakeri*|
|Columbidae||Red-bellied fruit-dove||Ptilinopus greyii|
|Loriidae||Palm lorikeet||Charmosyna palmarum*|
|Alcedinidae||Chestnut-bellied kingfisher||Todirhamphus farquhari*|
|Campephagidae||Melanesian cuckoo-shrike||Coracina caledonica|
|Campephagidae||Long-tailed triller||Lalage leucopyga|
|Sylviidae||Guadalcanal thicketbird||Megalurulus whitneyi|
|Acanthizidae||Fan-tailed gerygone||Gerygone flavolateralis|
|Monarchidae||Vanikoro monarch||Mayrornis schistaceus*|
|Monarchidae||Buff-bellied monarch||Neolalage banksiana*|
|Monarchidae||Black-throated shrikebill||Clytorhynchus nigrogularis*|
|Monarchidae||Southern shrikebill||Clytorhynchus pachycephaloides|
|Monarchidae||Vanikoro flycatcher||Myiagra vanikorensis*|
|Monarchidae||New Caledonian flycatcher||Myiagra caledonica|
|Rhipiduridae||Streaked fantail||Rhipidura spilodera|
|Zosteropidae||Santa Cruz white-eye||Zosterops santaecrucis*|
|Zosteropidae||Yellow-fronted white-eye||Zosterops flavifrons*|
|Zosteropidae||Sanford's white-eye||Woodfordia lacertosa*|
|Meliphagidae||New Hebrides honeyeater||Phylidonyris notabilis*|
|Meliphagidae||Dark-brown honeyeater||Lichmera incana|
|Meliphagidae||Cardinal myzomela||Myzomela cardinalis|
|Estrildidae||Royal parrotfinch||Erythrura regia*|
|Sturnidae||Polynesian starling||Aplonis tabuensis*|
|Sturnidae||Rusty-winged starling||Aplonis zelandica*|
|Sturnidae||Mountain starling||Aplonis santovestris*|
|An asterisk signifies that the species' range is limited to this ecoregion.|
There are seventy-nine bird species in Vanuatu, of which an amazing thirty species are endemic or near endemic (Table 2). The dropoff in diversity seen in other animal groups as one moves east from New Guinea is consistent with that seen in birds in Vanuatu. Whereas New Guinea has seventy-one families and subfamilies of birds, and the Solomons have forty-four, Vanuatu has thirty-one.
Vanuatu has an almost exact correspondence with the Vanuatu and Temotu 'Endemic Bird Area' (EBA). This EBA contains thirty restricted-range bird species. The Santa Cruz Islands (Temotu Province) have enough endemic species to qualify as an important EBAs by themselves. Fifteen bird species in the EBA are found nowhere else in the world. The Vanuatu scrubfowl (Megapodius layardi), Santa Cruz ground-dove (Gallicolumba sanctaecrucis), Vanuatu imperial-pigeon (Ducula bakeri), chestnut-bellied kingfisher (Todirhampus farquhari), royal parrotfinch (Erythrura regia), and Santo Mountain starling (Aplonis santovestris) are all considered vulnerable. The Tanna ground-dove (Gallicolumba ferruginea) is presumed to be extinct; no specimens have ever been collected.
Floristically, Vanuatu follows the pattern of the other outlying Melanesian islands: a decrease in diversity as one moves east from New Guinea. The Santa Cruz islands are a different phytogeographic unit from the rest of Vanuatu. Whereas the Santa Cruz Islands have two of the twelve common tree species found in the Solomons (Campnosperma brevipetiolata and Calophyllum vitiense), Vanuatu has only one: Pometia pinnata. Vanuatu is also more closely related to Fiji than to New Caledonia despite the current physical positions of the islands.
Between November and April of each year Vanuatu is subject to tropical cyclones, which are an important source of natural disturbance to the islands' forests. Cyclones and associated flooding occur at intervals of approximately every thirty years, and damage is enormous: up to 30 percent of forests are affected on some islands.
Vanuatu is the easternmost limit of the range of the saltwater crocodile, Crocodylus porosus, and is also home to the endangered Fiji banded iguana, Brachylophus fasciatus.
Ninety percent of the population is engaged in subsistence farming in rural areas, and 41 percent of the nation of Vanuatu is considered to have average or better agricultural suitability. This fertile land is not spread evenly among the islands, however. There is a growing emphasis on cash crops (cocoa, copra), and clearing for plantations and cattle has occurred. Commercial logging has intensively focused on two species: kauri (Agathis macrophylla) and sandalwood (Santalum austrocaledonicum). Sandalwood was almost eliminated by the end of the nineteenth century.
Severe cyclones, volcanic eruptions, and earthquakes are regular events in Vanuatu, and although these are natural events, their effects can be exacerbated by human disturbance of watersheds and remaining forest areas.
There are no protected areas in Vanuatu. Establishing protected areas is problematic because of customary land rights: 99 percent of the land is owned by village people.
Types and Severity of Threats
Although the potential area available for commercial forestry is limited by topography, available commercial species, cultivation, and cyclone damage, remaining lowland forests are under great pressure from logging companies.
Several bird species in Vanuatu are vulnerable simply because of their small natural ranges. Though subject to reduction by cyclones and consumed by almost all rural Vanuatuans, flying-fox populations seem healthy. The saltwater crocodile population has been reduced by hunting and cyclones.
Justification of Ecoregion Delineation
Distinct island groups were placed in their own ecoregions: the Solomon Islands rain forests, and the Vanuatu rain forests. We followed Stattersfield et al. in delineating these ecoregions. MacKinnon did not extend his assessment beyond the island of Bougainville in the Solomon Islands. However, we followed Bouchet et al. and separated the distinctive dry forests in New Caledonia from the moist forests to delineate the New Caledonia rain forests and the New Caledonia dry forests. Stattersfield et al. did not show this distinction.
Udvardy placed all the ecoregions in the New Guinea and Melanesia bioregion, with the exception of New Caledonia, into the Papuan biogeographic province of the Oceanian Realm. New Caledonia was placed in the New Caledonian biogeographic province.
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