The biodiversity of New Caledonia is of exceptional biological and paleoecological interest. It is frequently referred to as a biodiversity hotspot. The country is a large South Pacific archipelago with a total land area of more than . The terrain includes a variety of reefs, atolls, small islands, and a variety of topographical and edaphic regions on the largest island, all of which promote the development of unusually concentrated biodiversity. The region's climate is oceanic and tropical.
New Caledonia is separated from the nearest mainland by more than of open sea. Its isolation dates from at least the mid-Miocene, and possibly from the Oligocene, and that isolation has preserved its relict biota, fostering the evolution of wide ranges of endemic species.
Location and description
New Caledonia lies on the southernmost edge of the tropical zone, near the Tropic of Capricorn. It is part of the Melanesia subregion. It includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of Pines, the Chesterfield Islands in the Coral Sea, and a few remote islets.
The archipelago is about east of Australia and 1500 km, 1800 km and 1200 km from New Zealand, Papua New Guinea and Fiji respectively. A few lesser islands are closer, but now provide no convenient island-hopping path by which animal species could pass either to or from major mainlands. Some plants, invertebrates, sea mammals, and many flying species as aquatic birds, parrots, and bats have spread to new locations, either under their own power or due to freak events such as storms, or have been transported by humans. Some plant species have colonized new areas by means of seed carried by ocean currents.
Some animal and plant species have reached New Caledonia from surrounding regions and in turn, some New Caledonian species have successfully extended their ranges into the Pacific Ocean area. Other New Caledonian species or their close relatives are found in regions remote from the archipelago. For example, the New Caledonian parakeet is known to be the basal species in the genus Cyanoramphus, which has spread to many Pacific islands. Many bats and birds that rely heavily on fruit for their diet, including members of the families Cotingidae, Columbidae, Trogonidae, Turdidae, and Toucan, swallow seeds, then regurgitate them or pass them in their faeces. Such seed dispersal (ornithochory) has been a major mechanism of seed dispersal across ocean barriers. Seeds of grasses, spores of algae, and the eggs of molluscs and other invertebrates may stick to the feet or feathers of birds, particularly migratory or aquatic birds, and in this way may travel long distances.
The main island, Grande Terre hosts multiple habitats under the influence of varied precipitation, geology, edaphic factors and altitude. New Caledonia has several biotopes, including dense evergreen forests, maquis shrubland, sclerophyllous forest (dry forest), wetlands, savannas, and halophytic vegetation. The island has two main ecoregions: the greater area is occupied by the eastern New Caledonia rainforest while the now-fragmentary New Caledonia dry forest runs along the west coast.
The most conspicuous aspects of the New Caledonian marine environment are associated with the surrounding coral reef.
Such circumstances may be expected in general to promote biodiversity, but in the case of New Caledonia, a striking feature is the intense biodiversity in such a small land area. Presumably this is partly due to the edaphic and topographic features that define a number of discrete regions and ecological gradients. However, the local species do not always occupy all the potential niches, leaving the territory vulnerable to certain forms of invasion.
The larger flora include Nothofagus, Beilschmiedia, Adenodaphne, Winteraceae, Myrtaceae, southern sassafras (Atherospermataceae), conifers of Araucariaceae, Podocarpaceae, and Cupressaceae, and tree ferns.
Geologic origins
New Caledonia comprises fragments of the continental crust of Gondwana, dating to over one hundred million years ago (MYA), as well as volcanic material. The fragments apparently split from the Indo-Australian tectonic plate. Prevailing opinion holds that the archipelago represents the non-submerged regions of the continental fragment known as Zealandia. Zealandia broke away from the Australian part of Gondwana some 80-90 MYA. The separation of New Caledonia from mainland contact must have begun some tens of millions of years ago, probably during the Cretaceous period.