The biodiversity of New Caledonia is of exceptional biological and paleoecological interest. It is frequently referred to as a biodiversity hotspot.Myers, Norman; Mittermeier, Russell A.; Mittermeier, Cristina G.; da Fonseca, Gustavo A. B.; Kent, Jennifer. Biodiversity hotspots for conservation priorities. Nature 403, 853-858 (24 February 2000) | ; Received 22 September 1999 The territory 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.Présentation - L'Outre-Mer
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 Ramphastidae, 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 (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.Le Breton, Julien, Jourdan, Herve; Chazeau, Jean; Orivel, Jerome; Dejean, Alain. Niche opportunity and ant invasion: the case of Wasmannia auropunctata in a New Caledonian rain forest. Journal of Tropical Ecology (2005) 21:93–98. 2005 Cambridge University Press
The larger flora include Nothofagus, Beilschmiedia, Adenodaphne, Winteraceae, Myrtaceae, southern sassafras (Atherospermataceae), conifers of Araucariaceae, Podocarpaceae, and Cupressaceae, and tree ferns.Fujiwara, Kazue and Elgene O. Box (1999)."Evergreen Broad-Leaved Forests in Japan and Eastern North America: Vegetation Shift under Climatic Warming" in Conference on Recent Shifts in Vegetation Boundaries of Deciduous Forests F. Klötzli, G.-R. Walther, eds. Birkhauser, Basel.
Geologic origins
New Caledonia comprises fragments of the continental crust of Gondwana, dating to over one hundred million years ago (Ma), 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.Heads, Michael. "Biogeographical affinities of the New Caledonian biota: a puzzle with 24 pieces". Journal of Biogeography (J. Biogeogr.) (2010) 37, 1179–1201 Zealandia broke away from the Australian part of Gondwana some 80-90 Ma. The separation of New Caledonia from mainland contact must have begun some tens of millions of years ago, probably during the Cretaceous period.McLoughlin, Stephen. "The breakup history of Gondwana and its impact on pre-Cenozoic floristic provincialism." Aust. J. Bot. (2001) 49, 271–300
However, the view of the island as a surviving fragment of the Cretaceous period is obsolete. Islands from that time are partly or fully submerged. Most modern New Caledonian terranes formed via accretion of oceanic island arcs and seamounts. The biota evolved as metapopulations on islands that changed constantly until they merged into the archipelago. This hypothesis that the islands and their biota emerged about 37 Ma during the Oligocene better explains the organisms that occur in New Caledonian biota.New Caledonian lineages of Psychotria (Rubiaceae) reveal different evolutionary histories and the largest documented plant radiation for the archipelago
In the Carboniferous and Permian, New Zealand and New Caledonia were on the periphery of Gondwana, which included Africa, South America, Antarctica, India, New Zealand and Australia. Paleomagnetic data locate New Caledonia as originally near the South Pole. In the Triassic and early Jurassic, Gondwana moved northward, warming the eastern margin. New Caledonia separated from Australia and New Zealand during the breakup of the super-continent, separating from Australia at the end of the Cretaceous (66 Ma) and probably completing its separation from New Zealand in the mid-Miocene. However, as with any plate tectonic process, the process was protracted and in this region it was exceptionally complex. Many questions remain to be resolved.Grandcolas, Philippe; Murienne, Jerome; Robillard, Tony; Desutter-Grandcolas, Laure; Jourdan, Herve; Guilbert, Eric; Deharveng, Louis. New Caledonia: a very old Darwinian island? Phil. Trans. R. Soc. B (2008) 363, 3309–3317 Published online 2 September 2008
The island soils derived largely from ultramafic rocks and have been a refuge for many native flora species that have adapted to their composition a long time ago; such flora can survive on acid soils with unfavourable compositions of nutrient elements. On New Caledonia examples of such soils commonly have an excess of magnesium, plus unusually high concentrations of phytotoxic compounds of heavy metals such as nickel. Not many invader species can compete successfully with plants adapted to such challenging soils.
The native flora evolved many extremophile species that thrive in environments sufficiently toxic to put invasive plants at a disadvantage. Many areas, mainly on Grand Terre have some very high concentrations of metalliferous rocks. Their mineral content is poorly suited to most foreign species of plants.Dossier > La flore de Nouvelle-Calédonie - Première partie
Ultramafic rocks also contain elevated amounts of chromium and nickel which may be toxic to plants. As a result, a distinctive type of vegetation develops on these soils. Examples are the ultramafic woodlands and barrens of the Appalachian mountains and piedmont, the "wet maquis" of the New Caledonia rain forests, and the ultramafic forests of Mount Kinabalu and other peaks in Sabah, Malaysia. Vegetation is typically stunted and is sometimes home to endemic species adapted to the soils.
Often thick, magnesite-calcrete caprock, laterite and duricrust forms over ultramafic rocks in tropical and subtropical environments. Particular floral assemblages associated with highly nickeliferous ultramafic rocks are indicative tools for mineral exploration. Weathered ultramafic rocks may form lateritic nickel ore deposits.Golightly, J.P. (1981): Nickeliferous Laterite Deposits. Economic Geology 75, 710-735Schellmann, W. (1983): Geochemical principles of lateritic nickel ore formation. Proceedings of the 2. International Seminar on Lateritisation Processes, São Paulo, 119-135
Early organisms The marine fauna of the period, separate from that of the southwest Pacific, was distinguished as the "Maori province". Gondwana began its fragmentation in the middle and upper Jurassic, and the arrival of benthic invertebrate fauna is visible in fossil deposits. The Cretaceous marked the appearance of marine invertebrate fauna of southern origin. It was then that angiosperm flora such as Nothofagus and Proteaceae colonized New Zealand and New Caledonia, from South America, along the Antarctic margin of Gondwana.
At the beginning of the Tertiary, New Zealand and New Caledonia moved north to a warmer climate. This led to a long period of evolution in near complete isolation. New Caledonia's natural heritage includes species whose ancestors were present on New Caledonia when it broke away from Gondwana; not only species but entire genera and even families are unique to the island.
Evolution and history
The species of the archipelago of New Caledonia are relicts of a type of vegetation which earlier covered much of the tropics of the Earth, including much of the mainland of Australia, South America, Antarctica, South Africa, and North America. Although tropical cloud forests disappeared during the glaciations, they re-colonized large areas during successive geological eras when the weather was favorable again. At other times they were replaced by more cold-tolerant or drought-tolerant sclerophyll plant communities. Many of the then existing species became extinct because they could not cross the barriers posed by new oceans, mountains and deserts, but others found refuge as species relict in coastal areas and islands.
When the large landmasses became drier and with a harsher climate, this type of forest was reduced to those boundary areas. Although some remnants of archaic rich flora still persisted in coastal mountains and sheltered sites, their biodiversity was reduced. The location of the New Caledonian Islands in the Pacific Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate which has allowed these communities to persist to the present day.
The ecological requirements of many of the species are those of the laurel forest, and like most of their counterparts laurifolia in the world, they are vigorous species with a great ability to populate the habitat that is conducive. The geographical isolation and special edaphic conditions helped to preserve it too. Some species are even specialized in nickel hyperaccumulation such as the Sapotaceae Sebertia acuminata.