The islands were created by the subduction of the northward-moving Australian Plate beneath the Pacific Plate. The surface geology of Vanuatu consists mostly of Pliocene-Pleistocene volcanic rocks and uplifted coral limestone. The Santa Cruz Islands have areas of both uplifted limestone and volcanic ash over limestone. The oldest rocks in Vanuatu are 38 million years old. The Santa Cruz islands are younger, with the oldest rocks less than 5 million years old.[2]
Most of the islands are low-lying. The largest island is Espiritu Santo (3,955.5 km2). The highest peak is Mount Tabwemasana on Espiritu Santo (1,879 m).
Nendö, also known as Santa Cruz, is the largest of the Santa Cruz Islands with an area of 519 km2. Vanikoro is 190 km2, and Utupua is 69 km2. The highest peak in the Santa Cruz islands (924 m) is on Vanikoro. Nendö reaches over 500 meters elevation, and Utupua 350 m. They are made mostly of basaltic volcanic rocks of Pliocene origin, less than 5 million years old. The southeastern lowlands of Nendö are composed of uplifted Pleistocene reef limestone.[6]
Smaller islands in the group include Tinakula (8 km2 and 800 meters elevation), a conical active stratovolcano 30 km north of Nendö, and the Reef Islands northeast of Nendö, composed of uplifted Pleistocene reef limestone and rising only 5 meters above sea level. The Duff Islands are a small chain with four main islands about 130 km northeast of Nendö, with a combined area of 14 km2 and which rise up to 300 m elevation. Tikopia (5 km2), Anuta (1 km2), and Fataka (5 km2) are small isolated islands east and southeast of Vanikoro.[6]
Climate
The ecoregion has a tropical wet climate. The windward southeastern sides of the islands receive more rainfall. The leeward northwestern slopes of islands have a distinct dry season between April and October. Tropical cyclones occur regularly.[2]
Flora
The natural plant communities on the islands include lowland rain forest, montane rain forest, seasonal forest and scrub, coastal strand, mangroves, vegetation on recent volcanic rocks, and secondary vegetation.[2]
Lowland rain forest occurs on the southeastern, or windward, sides of Vanuatu's islands. There are several lowland rain forest types. Complex forest scrub densely covered with lianas is the most widespread forest type on the larger northern islands. Other types include high- and medium-stature forests, alluvial and floodplain forests, and mixed-species forests without conifers. Agathis-Calophyllum lowland forest is found on the southern islands of Erromango and Aneityum.[2]
In Vanuatu, montane rain forests extent from as low as 500 meters elevation up to patches of stunted cloud forest on the islands' highest peaks. They include the conifers Agathis macrophylla and Dacrycarpus imbricatus, together with broadleaf evergreen trees Metrosideros vitiensis, Syzygium spp., Pterophylla spp., Geissois spp., Quintinia spp., and Ascarina spp.[2] The tree ferns Cyathea and Dickinsonia are common, and the endemic palm Clinostigma harlandii is found on the islands Ambrym, Aneityum, and Erromango.[2]Podocarpus vanuatuensis is a Vanuatu endemic, native to Aneityum and Erromango. Agathis silbae is endemic to the Cumberland Peninsula and Mount Tabwemasana, also known as Santo Peak, on the west coast of Espiritu Santo, from 450 to 760 meters elevation. It is a large emergent tree in lower montain rainforest on the wetter western and northwestern slopes of Espiritu Santo's central mountain range, with an average annual rainfall of about 4,500 mm. Associated trees include Calophyllum neo-ebudicum, Cryptocarya turbinata, Didymocheton sp., Myristica sp., and Podocarpus sp.[7]Metrosideros tabwemasanaensis is a tree endemic to the montane forests of Mount Tabwemasana.[8]
Seasonal forest, scrub, and grassland grow on the leeward sides of the islands. Semideciduous Kleinhovia hospita-Castanospermum australe forests are a transition between rain forest and dry forest, and include some rain forest species. Forest of gaiac (Acacia spirorbis) is found in drier areas, with a canopy up to 15 meters high. Thickets and savannas of the introduced tree Leucaena leucocephala and grasslands are also found on the leeward sides of the islands.[2]
The Pacific boa (Candoia bibroni), also known as Bibron’s bevel-headed boa, the Solomon Islands boa, or the Pacific ground boa (among several other names), is native to the island and surrounding region. It is unique among Boidae snakes for its “bevel” or “spade”-shaped snout, used for digging; perhaps the closest comparable species would be the Kenyan sand boa, which spends much of its time burrowing, where it will lie in wait to ambush its passing prey above.[citation needed]
^ abEric Dinerstein, David Olson, et al. (2017). An Ecoregion-Based Approach to Protecting Half the Terrestrial Realm, BioScience, Volume 67, Issue 6, June 2017, Pages 534–545; Supplemental material 2 table S1b. [1]
^ abcMueller-Dombois, Dieter, and Francis Raymond Fosberg (1998). Vegetation of the tropical Pacific islands, pp. 84-161. Springer. ISBN 9780387983134, 0387983139
^Pillon, Yohan (2018). A new species of Metrosideros (Myrtaceae) from Vanuatu and notes on the genus. Phytotaxa Vol. 347 No. 2: 13 April 2018: 197–200. DOI: https://doi.org/10.11646/phytotaxa.347.2.10
^BirdLife International (2020) Endemic Bird Areas factsheet: Vanuatu and Temotu. Downloaded from http://www.birdlife.org on 02/06/2020.
