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Plaine des Lacs, "hot point" of biodiversity

The New Caledonian flora and fauna are distinctive due to the fact that it is:
• A continental island, the remains of Gondwana, from which it has been separated for 60-80 million years,
• Geographical isolation (its nearest neighbour Australia is over 1200 km away)
• The abundance of peridotite rocks which were put in place 35 to 40 million years ago (Guillon, 1975 in Jaffré (1980)), the origin of particular soils which living organisms had to adapt to.

Plaine des Lacs, "hot point" of biodiversity
This remarkable endemism and this specific wealth places New Caledonia among the priority zones as regards conservation of biodiversity (UICN, WWF, 1994). The island therefore has 4 of the 238 priority ecoregions defined by the WWF, which is the "soft water" ecoregion of New Caledonia (Flouhr and Mary 2005).

The flora of New Caledonia is particularly rich as over 3,000 species has been listed in a territory of 19,105 km² (ratio of 0.157). By way of comparison, New Zealand has 1,460 species for 256,000 km² (ratio of 0.005) while New Guinea has 20,000 for a surface area of 800,000 km² (ratio of 0.025).

But the interest in Caledonian flora is also in its originality. Actually, out of around 3,300 species listed, we count 75 % of endemic species (the area of natural distribution is limited to New Caledonia). On the ultramafic massifs, the proportion of endemic species is even higher as it reaches 90%.

Plaine des Lacs, "hot point" of biodiversity
In the Plaine des Lacs several remarkable plants are to be found, all endemic: Nothofagus spp. (Nothofagus discoidea classified VU by the IUCN), Xanthost mon aurantiacum, Gymnostoma deplancheanum, Dacrydium araucarioïdes. The site is home to three threatened gymnosperms: Dacrydium guillaumini, Retrophyllum minor and Neocallitropsis pancheri (respectively classified CR, EN and VU by the IUCN).

The fauna presents a high level of endemism in the majority of the groups: for example, for the known aquatic insects, over 75% of species are endemic to New Caledonia (Mary, 1999). The rate of endemism is 17.2% for freshwater fish and 37.8% for freshwater crustaceans (Marquet et al., 2003).

As regards the Plaine des Lacs, and despite the near absence of populations of water birds, the zoological endemism there is very high:
• two types of Gastropods are strictly endemic there: Glyptophysa (family of the Planorbidae, with one species classified EN by the IUCN) and Heterocyclus (family of the Hydrobiidae, with two species classified EN by the IUCN) to which must be added one type and 4 species not yet described,
• 5 species of decapod crustaceans of the Paratya type (of which only one single species is known outside of New Caledonia),
• the Copepode Boeckella spinogibba and the fish Galaxias neocaledonicus (which is classified CR by the IUCN).

Mots clés : Source Province Sud

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