New Caledonia harbours 18 species of the Araucariaceae family of conifers, all of them endemic. On the global scale, that figure represents 45% of all species of this family. They are divided between two genera, Agathis (or kaoris) and Araucaria (columnar pines), consisting respectively of 5 and 13 species. Several of them are important economically, as a source of timber, and also have an ecological significance owing to their frequent occurrence on diverse substrates in plant communities ranging from pioneer associations to dense tropical rainforest level. Moreover, the stands of columnar pines give the New Caledonian landscape an impressively unusual character. Araucaria columnaris, widely planted near villages, also possesses a symbolic cultural value in the Kanak tradition.
The five species of Agathis and the 13 of Araucaria are on IUCN Red List of endangered species (1). The continuous regression of populations of several species, brought on by human-induced bush fires, mining and urban expansion is putting their genetic integrity at risk. Yet little research has been devoted to New Caledonia Araucariaceae, in spite of their special features (richness, unusual character, economic and heritage significance). For this reason botanists from the IRD, who for many years have been studying the local flora, and from the Natural Resources Department of the Southern Province of New Caledonia, have produced a bibliographic review of current knowledge on this family. Many questions remain concerning the identification of certain species of the genus Araucaria, owing to polymorphism of vegetative characters. Furthermore, although it is recognized that the Araucariaceae family has diversified since the emplacement of ultramafic igneous rocks (2) 39 million years B.P., molecular genetics investigations have not yet elucidated the origin and phylogeny of the different species.
The Araucariaceae in New Caledonia are all trees. The Agathis species are voluminous trees developing some of the densest, most closed canopy of the forests. Agathis lanceolata can be up to 2.5 m in diameter and reach 40 m high. Four of the five Agathis species are essentially forest trees. Only A. ovata develops also in the evergreen heath-like maquis of the mining areas. Two species are strictly associated with ultramafic substrates (A. lanceolata and A. ovata), two with acid rocks (A. corbassonii and A. montana), and one species is spread over both types of substrate (A. moorei).
The diameters of the Araucaria species are not so large, but these trees commonly reach heights of about 50 m. They are found in the forest and the maquis, most often on steep slopes or on ridges exposed to the prevailing winds. Ten species are encountered only in zones with ultramafic rocks. One species (A. montana) grows just as well on ultramafic rocks as on acid rocks and another (A. schmidii) mainly on acid rocks. There is just one species (A. columnaris) which favours mainly coastal forests on calcareous formations. Among the species encountered on ultramafic rocks, three (A. subulata, A. biramulata, A. bernieri) are essentially forest adapted, whereas the other seven grow in both the forest and the maquis. These distribution patterns express a clear affinity of Araucaria for exposed sites and for substrates originating from ultramafic rocks which often act as refuge areas where interspecific competition is less fierce. That situation favours specialized species, adapted to the strong constraints imposed by the available habitats.
In the maquis, Agathis ovata and the different species of Araucaria appear capable of continuous regeneration. Nevertheless, although the tall individual trees are fairly fire-resistant, the regeneration process is often thwarted by fires which destroy the plant embryos and young plantations. In the forest, the Araucaria and the Agathis dominate the high ground and regrowth only develops with the help of gaps caused by clearances, which indicates heliophilous affinities (3) of the two genera.
This state-of-the-art review of knowledge on the Araucariaceae could provide keys to a better understanding of the origins of the species diversity, their affinities and the role of each in the flora of New Caledonia. The scientists consider that it is now necessary to protect better the endangered Araucariacaean species in order to conserve the biodiversity of this plant family. They recommend modification and reinforcement of the classification of some of these species relative to the IUCN 2000 Criteria.
(1) IUCN, International Union for the Conservation of Nature, now renamed World Conservation Union.
(2) Nearly one-third of New-Caledonian soils are derived from ultrabasic massifs particularly rich in nickel and chromium but poor in nutrient elements essential for plant growth, such as nitrogen, phosphorus, calcium or potassium.
(3) especially appreciating sunlight.
FOR FURTHER INFORMATION
J. Manauté, T. Jaffré, J.-M. Veillon, M.-L. Kranitz, Revue des Araucariaceae de Nouvelle-Calédonie, Publication IRD/Province Sud de la Nouvelle-Calédonie, 2003, 28 pages.