Forest Vines to Snow Tussocks: The Story of New Zealand Plants
New Caledonia and Other Pacific Islands
New Caledonia and Other Pacific Islands
Although only 400 km long, New Caledonia is composed of continental rocks similar to those of New Zealand and has a rich and, in many ways, remarkable flora. Conifers are particularly prominent with Araucarias, tall and pencil-like or of candelabra form, providing a distinctive character to many landscapes. Indeed, of the 19 species of Araucaria recognised for the world 13 are restricted to New Caledonia. Several species of Agathis (kauri) are also present, several genera of the family Podocarpaceae, including the only known parasitic conifer (Parasitaxus ustus) and 3 species of Libocedrus. Several old southern families of flowering plants are also strongly represented — Myrtaceae, Proteaceae, Epacridaceae, Cunoniaceae. The primitive family Winteraceae is centred in New Caledonia with 4 genera and about 16 species.
For the most part New Caledonia has a quite steep topography, but the mountains up to 1600 m in altitude are not high enough to support alpine vegetation. On the drier west of the island and on burnt sites in the east there are extensive open woodlands of Australian aspect dominated by Melaleuca quinquenervia with its spongy fire-resistant bark. As in Australia, the Melaleuca also grows in swampy sites and it has been suggested that prior to the arrival of human beings it may have been largely restricted to such places, becoming more widespread following destruction of rain forests on better drained sites by fires of human origin.
At lower elevations closed forests which are still intact share many genera with similar forests in Australia and New Guinea and to a lesser degree New Zealand.189 Strangling figs may occur as emergents. In places, particularly on ridge crests, there are also species of Araucaria and Agathis. A number of endemic palms are prominent as are some tree ferns, including Cyathea novaecaledoniae with its distinctive greyish trunks which attain heights of up to 30 m. The ferns Asplenium nidus and Drynaria rigidula are frequent as nest epiphytes.
At higher altitudes the montane rain forests are lower in stature, different in species composition and have more New Zealand links. The strangling figs of lower elevations give way to Metrosideros and the related Carpolepis, some species of which are frequently or occasionally initially page 230epiphytic. Similarly the nest fern epiphytes give way to Astelia novaecaledoniae. Weinmannia and other members of the Cunoniaceae, tree ferns and conifers of the family Podocarpaceae are important components of these forests.
Nothofagus occurs in patches mixed with other genera or in pure ridge crest stands, although not on all mountains. The species of Nothofagus, as in New Guinea, belong to the N. brassii group and some are notable for having unusually large leaves particularly at the juvenile stage (Fig. 70).
The most notable physical feature of New Caledonia as far as the plants are concerned is the unusual extent of ultramafic or 'serpentine' rocks, which occupy a third of the island. Unlike some similar sites elsewhere in the world New Caledonian serpentine supports a rich and distinctive flora190 in which conifers, Nothofagus, and the families Myrtaceae, Proteaceae, Epacridaceae and Casuarinaceae are prominent. Shrub and sedge associations are widespread, but there are also quite dense forests particularly at higher elevations.
Further into the Pacific to the east the Fijian Islands are largely volcanic although, according to some geologists, continental rocks underlie them. A small continental element in the flora includes ten conifers — a species of Agathis and several podocarp species in several genera — and the primitive flowering tree Degeneria vitiensis placed in its own family close to the Winteraceae.
Much further to the east, entirely volcanic and remote from any continent, Tahiti is the highest and largest island of French Polynesia. Geologists believe that Tahiti, as well as other similar islands, rose above the sea in isolation. It would follow that the ancestors of its flora must have arrived by overseas dispersal from already existing islands near and far and directly from continents or indirectly via intervening islands. Possible involvement of a proposed former continent Pacifica was considered in Chapter 1.
Tahiti, along with other very isolated islands, completely lacks certain plant groups. It has no conifers, no species of Nothofagus, no members of the Winteraceae or related primitive families nor of the southern page 231family Proteaceae. Of other important southern families the Myrtaceae is represented by Metrosideros and Decaspermum, the Cunoniaceae by Weinmannia and the Epacridaceae by Styphelia. Near sea level, native vegetation is virtually non-existent, but at higher levels there is a good cover. The forest is low, and in hollows and valleys is dominated by Weinmannia parviflora which, like the New Zealand Weinmannia racemosa, has compound juvenile and simple adult leaves and also often commences life as a low tree fern epiphyte. A long leaved Freycinetia is abundant and there are small orchid and fern epiphytes. Among small trees and shrubs are one large and one small-leaved species of Myrsine, a Meryta and in places a large-leaved Coprosma and the small tree Fuchsia cyrtandroides. In some valleys there are dense tree fern forests which may follow forest clearance as in New Zealand. The tree ferns are species of Cyathea and at least one has the unusual habit of forming more or less spherical bulbils below the leaf crown which drop off to grow into new plants.
On narrow ridge crests species of Metrosideros are conspicuous along with some of the plants from the valleys and in more open places a small-leaved Styphelia. One species each of Ascarina, Macropiper and Ilex are also present. On the ground and sometimes epiphytic is an Astelia and in moist places an Elatostema.
The Tahitian peaks are not high enough for the latitude to support alpine plants.
The Hawaiian Islands lie in the tropical north Pacific. The islands in the group are mostly larger than Tahiti and the largest and southernmost, Hawaiʻi itself, has dome-like volcanoes, some still active, rising to over 4000 m. This is high enough to provide alpine conditions.
Hawaiʻi shares with New Zealand and Tahiti such genera as Metrosidews, Astelia and Coprosma, but has more species of them than Tahiti. It lacks Weinmannia, a genus important in some Tahitian and New Zealand forests. Species and varieties of Metrosideros dominate in most Hawaiian forests, particularly on the island of Hawaiʻi where some forms colonise lava flows and may form trees up to 30 m in height. In time other less light-demanding and shorter species enter the forests. They belong to such genera as Sapindus, Ilex, Osmanthus (some unite the Hawaiian species of this genus with Nestegis of New Zealand), Pittosporum, Myrsine and page 232Elaeocarpus. Tree ferns of the genus Cibotium may be common and sometimes bear a species of Cheirodendron (a genus related to Pseudopanax) as an epiphyte. There are also a few larger-leaved species of Coprosma, a long leaved Freycinetia and several species of Astelia both terrestrial and epiphytic. The Lobelia family has undergone remarkable development in Hawaiʻi with several genera and many species of shrubs and small trees, some of which are found in moist forests.
Apart from Metrosideros the only other large tree species is Acacia koa. This may be a component of Metrosideros forests or may dominate more open woodlands.
Above tree limit on the high volcanoes of Hawaiʻi and Maui there is low shrubby vegetation on well drained sites reminiscent of the mountain shrubland of the volcanic Mt. Ruapehu of New Zealand. Close inspection however reveals very few species including a Sophora, a small-leaved Styphelia, a Vaccinium with bright red, shiny berries, a few small-leaved Coprosmas, and a few ferns.
At higher levels still is a volcanic desert with few alpine species — a few grasses, small ferns, a few herbs in such genera as Fragaria and Geranium, and small shrubs such as the trailing small-leaved Coprosma ernodioides. The most remarkable alpine is the silversword (Argyroxiphium sandwicense) of the daisy family which is found only on Mt. Haleakela on Maui. It is somewhat like the Celmisias in New Zealand with sword-like leaves, but much larger, with the silvery-white leaves almost spherically arranged. The tall reddish flower heads are not unlike those of some of the Pleurophyllums of the New Zealand subantarctic.
Subalpine and alpine bogs have a much closer cover of plants. In less wet places there are dwarf shrubs of Metrosideros and other genera, but the wettest parts are essentially cushion bogs with cushions of Oreobolus, some grasses and species of Astelia. Scattered rosette herbs include Droseras (sundews) and species of Plantago, Geranium and Brachycome.