Introduction

Captaincookia (Captaincookia margaretae), New Caledonia, France. (Photograph by Arnaud Greth)

The dry forests of New Caledonia contain a unique assemblage of plants with fifty-nine endemic species, including the famous Captaincookia margaretae. The ecoregion has been severely degraded by human activity, and immediate conservation action is needed to ensure the long-term survival of many species.

Location and General Description

The islands of New Caledonia are remarkable for their number of plant species, plant endemics, and the ancient character of much of the flora. New Caledonia is located in the southwest Pacific Ocean about 1,200 kilometers (km) east of Australia and 1,500 km northeast of New Zealand. The main island of Grande Terre runs in a north-south orientation and is 16,372 square kilometers (km²). Unlike the much smaller neighboring islands, which are volcanic and recent in origin, Grand Terre is an original piece of Gondwanaland. It separated from Australia 85 million years ago and has maintained its current isolation from other landmasses for more than 55 million years. Isolation and an ancient source of plant life are major factors leading to the island's diverse plant life, but they are not the only factors. Grand Terre has an extremely diverse soil substrate, with ultramafics forming about one-third of the island. It is also very diverse topographically and climatically. Grand Terre is the only high island of New Caledonia, with a mountain chain running down the center of the island and five peaks exceeding 1,500 meters (m). Many smaller ranges and valleys run counter to the island's north-south orientation.

Tiae, New Caledonia. (Photograph by David Olson)

The New Caledonia dry forests ecoregion is found only on the western side of Grand Terre, where the average annual rainfall is much lower than on the rest of the island. Rainfall on Grand Terre is highly seasonal. Trade winds bring the rains, which usually come from the east. The western side of the island receives about 1,200 millimeters (mm) of rainfall annually, although in some years it may be as low as 250 mm. However, because of the orographic nature of the island's rainfall, the average annual rainfall is about 2,000 mm for the low-elevation eastern Grand Terre and 2,000-4,000 mm at high elevations.

Dry forest vegetation used to make up most of the lowland portions (below 300 m) of the western side of Grand Terre, although this ecoregion has been greatly reduced and exists mainly in disjunct forest patches. In the natural state, these dry forests are dense, contain many vines, and reach heights of 5-15 m. The vegetation is often dominated by Acacia spirorbis and Leucaena leucocephala (an introduced species). Other dominants include Rubiaceae of the genera Canthium and Gardenia, Pittosporum, Dodonaea, and Premna, and Verbenaceae genera. The dry forests also have a thick, unstratified understory of shrubs and grasses. Near the coast the typical dry forests give way to stands of Cycas circinalis, the only gymnosperm typical of the ecoregion.

Biodiversity Features

The New Caledonia dry forests ecoregion contains 379 native plant species (phanerogam), 59 of which are found only in the dry forests. The total number of species and number of endemics are substantial but still less than the numbers for the New Caledonia rain forests. The dry forests also differ from the moist forests in their composition. The latter are famous for having the greatest diversity of gymnosperms anywhere, a high number of plants in the primitive flowering plants of the genus Pandanus and family Winteraceae, and a great number of endemic palms. The dry forests have only one gymnosperm and none of these other taxa. Furthermore, the dry forests lack all five of the plant families endemic to New Caledonia. Still, the dry forests contain many extremely interesting plants, such as Captaincookia margaretae (Rubiaceae), the only member of its genus.

Few if any of the vertebrates of New Caledonia are endemic to the dry forests. However, there are five near-endemic mammals (Table 1) and twenty-three near-endemic bird species (Table 2), most of which are shared with the New Caledonia moist forests. Invertebrates are less numerous in dry forests than in the rain forests, but many that live there are likely to be endemic.

Current Status

Tropical dry forests are the most threatened tropical forest type worldwide, and the dry forests of New Caledonia are no exception. With less than 2 percent remaining in isolated patches, the dry forests are by far the most endangered vegetation type in the territory. Comparisons between the biological features of the dry forests and the rain forests of New Caledonia are almost irrelevant because the remaining dry forests are so tiny: 10,000 hectares (ha), an area slightly larger than New York's Manhattan Island. The high rates of endemism also occur with a high turnover, meaning that almost all remaining dry forest patches are likely to contain complementary assemblages of species found nowhere else and should be preserved. The rest of the dry forest ecoregion has been replaced by ranchland or introduced species.

Out of 117 dry forest plant species evaluated for IUCN classification, 59 (or 50 percent) are threatened (VU or higher). The first recorded plant extinction in New Caledonia occurred within the dry forests when a fire wiped out the only known population of Pittosporum tanianum, a very distinct species discovered in the mid-1980s. Given the reduced size of the dry forests, it is almost certain that many plants have gone extinct that were never described. This is likely given that all the current dry forests of New Caledonia are on top of sedimentary substrates and that large portions of dry forest on basaltic substrates have been completely destroyed.

The protected area network of New Caledonia is poor in both scope (covering 2.8 percent of the land area) and in the resources necessary to make the protected areas effective (Table 3). Almost all of the dry forests are in private hands, and of the six provincial parks in the dry forests, none are improving the conservation of the species living there. Jaffré et al. consider the dry forests completely unprotected. Even the traditional act of putting up fences would not be sufficient to protect species from fires such as the one that wiped out the only known populations of Pittosporum tanianum.

Types and Severity of Threats

With so little habitat remaining, these forests are vulnerable to conversion threats (agriculture, rangelands), fire, introduced species, and natural disturbances. Their ability to survive is highly threatened even with immediate intervention.

Introduced species pose a grave threat to the biodiversity of New Caledonia. Pigs, goats, cats, dogs, and rats present problems for native species here, as they do on many islands throughout the world. The introduced rusa deer (Cervus timorensis) is widely hunted. In addition to deer trampling and grazing understory plants, people often start fires to attract deer to the new growth that follows. In addition to setting fire for deer, Bouchet et al. explained, "lighting fire has also become an expression of protest from young rural unemployed males. It is not exaggerated to write that fires plague New Caledonia, west and east coast alike, from July to December." Many of the native species are not adapted to be fire resistant, and as a result some introduced species as well as native species that are fire resistant are taking over. The Neotropical ant (Wassmannia auropunctata) that was brought in with Caribbean pine cultivation is greatly diminishing native lizard and invertebrate abundance and diversity. The severe impacts of this ant may determine the long-term persistence of native communities in this ecoregion.

New Caledonia is a prosperous territory of France, and this prosperity affects the future of its biodiversity. The per capita income of New Caledonia is similar to that of New Zealand and Australia. The prosperity means that many of the problems of rapid population increases found in other tropical forested areas are not prevalent. However, because New Caledonia, as part of France, is considered a developed country, it does not qualify for funds to protect biodiversity through traditional international sources. Meanwhile, the French government has paid little attention to the conservation of New Caledonia's wealth of biodiversity.

Justification of Ecoregion Delineation

The New Caledonia rain forests ecoregion is based on the original extent of sclerophyllous forests appearing in Jaffré and Veillon.

Additional Information on this Ecoregion

• For a shorter summary of this entry, see the WWF WildWorld profile of this ecoregion.
• To see the species that live in this ecoregion, including images and threat levels, see the WWF Wildfinder description of this ecoregion.
• World Wildlife Fund Homepage