The Flora of New Caledonia's Calcareous Substrates
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The flora of New Caledonia’s calcareous substrates Philippe MORAT Laboratoire de Phanérogamie, Muséum national d’Histoire naturelle, 16 rue Buffon, 75005 Paris, France. [email protected]. Tanguy JAFFRÉ & Jean-Marie VEILLON Laboratoire de Botanique et Écologie Appliquées, I.R.D., BP A5, Nouméa, Nouvelle-Calédonie. [email protected] ABSTRACT Calcareous substrates occupy c. 3,800 km2 in New Caledonia (incl. 1,990 km2 in the Loyalty Islands) and are of various age and origin. A total of 488 spp. (16.1% of the total indigenous seed plants) grow on these substrates, 39.7% of which are endemic, far below the 76,9% level of the total flora. Among these, 401 spp. are merely tolerant of calcium, with a wide enough ecological amplitude to occupy other substrates, including 200 spp. that also grow on otherwise highly selective ultramafic soils. Only a core of 87 spp. are restricted to calcareous substrates and can truly be called calciphilous. They grow mainly in sclerophyllous and dense forests. The affinities and origins of this flora are analyzed and show stronger links with Australia and Malesia, a KEY WORDS result largely similar to those obtained for the floras as a whole. Many calcareous substrates, flora, threatened taxa are part of this flora, and require special measures to ensure New Caledonia. their protection. RÉSUMÉ La flore des substrats calcaires de la Nouvelle-Calédonie. Les substrats calcaires d’âge et d’origine diverses occupent en Nouvelle- Calédonie une surface d’environ 3800 km2 dont 1990 aux îles Loyauté. Au total, 488 espèces (16,1 % de la flore phanérogamique) croissent sur ces sub- strats avec un endémisme spécifique de 39,7 % nettement moins élevé que celui de la flore globale (76,9 %). Parmi ces espèces, 401 sont de large ampli- tude écologique et suffisamment tolérantes pour supporter d’autres types de substrats, dont 200 se retrouvent sur des sols issus de roches ultramafiques de composition chimique pourtant très sélective. Seul un lot de 87 espèces stric- tement inféodées au calcaire mérite d’être appelées calciphiles ; elles poussent essentiellement en forêts sclérophylles ou en forêts denses humides. Les affini- tés et les origines de cette flore sont discutées et montrent des liens plus ADANSONIA, sér. 3 • 2001 • 23 (1) : 109-127 © Publications Scientifiques du Muséum national d’Histoire naturelle, Paris. 109 Morat Ph., Jaffré T. & Veillon J.-M. marqués avec l’Australie et la Malésie, presque similaires à ceux déjà obtenus MOTS CLÉS pour l’ensemble de la flore néo-calédonienne. De nombreux taxons menacés substrats calcaires, flore, nécessitant des mesures spéciales de protection sont présents dans cette flore Nouvelle-Calédonie. calciphile. INTRODUCTION flysh, or they are associated with siliceous rocks (phtanites). In the Népoui area they are found in The range of rock types in New Caledonia is, conglomerates dating from the Miocene. along with its long isolation (separated from In certain places, calcareous rocks have been Australia since the end of the Cretaceous, some covered over by alluvial deposits derived from older 65 million years ago), one of the fundamental ultramafic rocks (Népoui, Pindaï, Pouembout for- causes of the exceptional richness of the territory’s est): as a consequence they are very magnesium- flora (3,021 native species of flowering plants), as rich. In the majority of cases, however, the well as its uniqueness (76,9% of those species characteristic features caused by the incorporation endemic), and all this despite the small size of of the ultramafic material do not over-ride those of the territory (19,100 sq. km, of which the the underlying calcareous substrates, which pro- main island of New Caledonia itself comprises duce soils rich in phosphorus and calcium. 16,900 sq. km) (MORAT et al. 1981). Those of coral reef origin (Fig. 3) occur in the Although the role of certain substrates, such as Loyalty Islands (including Walpole), the Ile des ultramafics, in influencing the uniqueness and Pins and along the coastal strip in the south-east distribution of the New Caledonian flora and of the main island. They are of Miocene origin vegetation types has been much studied (MORAT and emerged in the Quaternary. et al. 1984, 1986; JAFFRÉ 1976, 1980; JAFFRÉ et al. Only a detailed study of the flora growing on cal- 1984), that of the calcareous rocks is so far little careous soils, and particularly an analysis of the dis- understood. tribution of its species on all the other substrates found in the territory, can reveal whether there exists in New Caledonia a truly obligate calciphilous flora MATERIAL AND METHODS as found elsewhere (e.g. Madagascar), or whether it is a flora merely tolerant of calcium. Calcareous substrates outcrop in various places For this study, only indigenous species are taken in the territory (Fig. 1) and cover some 3,800 sq. into consideration. The others, both naturalized km., of which nearly 2,000 sq. km are in the or subspontaneous, being by definition alien (and Loyalty Islands and on the Ile des Pins. They can whose ecology may be different in their native be divided into two major categories: those derived habitats), cannot, logically, belong to the indige- from coral reefs and those of sedimentary origin nous assemblage of New Caledonian calcicolous (PARIS 1981a, 1981b). The latter are of diverse plants. So that the results can be compared with ages and have varying appearances. The oldest, those from earlier work (MORAT et al. 1984, dating from the Paleocene to the Lower Eocene, 1986, 1994; JAFFRÉ et al. 1987) relating to vegeta- occur in the Hienghène and Koumac areas as well tion types on other geological substrates (ultra- as on the west coast as far south as Bourail; in some mafic rocks), only seed-plants are considered here. places they are found as limestone pavement (karst lapiazé) (Fig. 2). Slightly younger calcareous sub- strates (Middle to Upper Eocene) occur sporadi- RESULTS AND DISCUSSION cally along the west coast, between Poum and 1. Flora of calcareous substrates Nouméa (Nouméa-Boulouparis valley, Baie de St. Vincent, Poya), and in the centre of the main As defined here, the indigenous seed-plant flora island (Table Unio, Col des Roussettes) as calcified growing on calcareous substrates comprises 110 ADANSONIA, sér. 3 • 2001 • 23 (1) Flora of New Caledonia’s calcareous substrates Miocene emerged in quaternary Lower Miocene Paleocene to upper Eocene Poum Koumac Hienghène Loyalty Islands Pouembout Col des Roussettes Pindaï Table Unio Népoui Poya Bourail 22° Boulouparis Baie de St. Vincent Nouméa 0 50 km Ile des Pins 166° Fig. 1. — Limestone substrate in New Caledonia (adapted from PARIS 1981). 488 species, representing 311 genera in 97 families the families, compared with just 16.1 % of the (Table 1). Comparison with the entire indigenous species represented in the New Caledonian flora, flora shows that the flora of calcareous substrates is are found on these substrates. relatively poor, comprising only 16.1% of the total, A single family (Euphorbiaceae) has 36 species, and has a lower level of endemism, with only 39.7% although the number decreases rapidly (Table 2): of its species restricted to the territory, compared the thirteenth family (Compositae), for example, with 76.9% of the entire flora. has only ten. At the family level, there are certain This relative paucity could be due in part to gaps that are worth pointing out. Most of the the smaller area occupied by these substrates, families of gymnosperms (with the exception of about 3,800 sq. km, and partly to human inter- one species each of Cycas and Araucaria), all ference, which has considerably degraded and the endemic families (with the exception of reduced the original vegetation, as well as to the Phelline comosa) and several families, primitive currently incomplete state of the floristic inven- (Winteraceae, Monimiaceae) and not tory of the vegetation types that occur on calcare- (Epacridaceae, Cunoniaceae), are absent from ous rocks. When compared with the entire New calcareous substrates. Moreover, certain families Caledonian flora, that of calcareous areas seems, very commonly occurring elsewhere [Liliaceae, on the other hand, to be more diversified at the Orchidaceae, Palmae, Pandanaceae, Asclepiadaceae, family and generic levels, rather than at the level Myrtaceae (especially Myrtoideae), Cyperaceae, of species. Thus 43% of the genera and 59% of Dilleniaceae, Flacourtiaceae and even Capparaceae] ADANSONIA, sér. 3 • 2001 • 23 (1) 111 Morat Ph., Jaffré T. & Veillon J.-M. TABLE 1. — Comparison of the indigenous calcareous flora with the entire indigenous phanerogamic flora. Species Genera Families Number Endemic % Number Endemic % Number Endemic % Entire flora 3,021 2,326 76.9 723 98 13.5 165 5 3 Calcareous flora 488 194 39.7 311 10 3 97 1 < 1 % 16.1 43 59 TABLE 2. — Largest families in the calcareous flora. TABLE 3. — Largest genera in the calcareous flora. Family Number of species Genus Number of species Euphorbiaceae 36 Diospyros 11 Gramineae 33 Phyllanthus 9 Leguminosae 28 Ficus 8 Myrtaceae 22 Sapindaceae 22 Syzygium 8 Apocynaceae 19 Myoporum 7 Rubiaceae 19 Ipomoea 6 Cyperaceae 17 Euphorbia 5 Convolvulaceae 14 Oxera 5 Rutaceae 12 Ebenaceae 11 Austromyrtus 5 Moraceae 11 Arytera 5 Compositae 10 Cupaniopsis 5 are very poorly represented on this type of sub- behind mangroves. But these original vegetation strate. types have in many cases (notably sclerophyll for- In view of the above mentioned diversification est) suffered damage through human activity and at the generic level (Table 3), it is not surprising have as a result been replaced by secondary for- that few genera are rich in species. The largest mations (secondary forest, savanna, thickets, genus (Diospyros) has only 11 species here, against weedy vegetation) in which an alien flora of cos- 29 for the total flora, while the next five genera mopolitan species thrives.