Grand Terre is a long island that runs approximately north–south, with a mountain range down the center with five peaks that exceed 1500 meters elevation.

The western slopes of Grand Terre, which are in the rain shadow of the central mountain range, are much drier, and are home to the New Caledonia dry forests ecoregion.

It has been isolated from other land masses since then, although a number of plants and animals have been able to cross the straits separating New Caledonia from neighboring islands.

New Caledonia's fauna and flora derive from ancestral species isolated in the region when it broke away from Gondwana many tens of millions of years ago.

On New Caledonia examples of such soils commonly have an excess of magnesium, plus unusually high concentrations of phytotoxic compounds of heavy metals such as nickel.

The laurifolia appears in mountains of the coastal strip of New South Wales in Australia, New Guinea, New Caledonia, Tasmania, and New Zealand.

Other typical flora include Winteraceae, Myrtaceae, southern sassafras (Atherospermataceae), conifers of Araucariaceae, Podocarpaceae, and Cupressaceae, and tree ferns.

Unlike many of the Pacific Islands, which are of relatively recent volcanic origin, New Caledonia is part of Zealandia, a fragment of the ancient Gondwana super-continent.

The islands still shelters an extraordinary diversity of endemic plants and animals of Gondwanan origin have spread to the southern continents later.

New Caledonia lies at the northern end of the ancient continent Zealandia, while New Zealand rises at the plate boundary that bisects it.

At Curio Bay, logs of a fossilized forest closely related to modern kauri and Norfolk pine can be seen that grew on Zealandia about 180 million years ago during the Jurassic period, before it split from Gondwana.

The lowland rain forests cover the Loyalty Islands, and the Iles des Pines and the lower elevations of Grand Terre.

The predominant conifers are Araucaria columnaris, A. bernieri, Agathis lanceolata, A. ovata (Araucariaceae), and Dacrydium araucarioides, Dacrycarpus vieillardii and Falcatifolium taxoides (Podocarpaceae).

Predominant angiosperm trees include Montrouziera cauliflora, Calophyllum caledonicum, Didymocheton spp., Neoguillauminia cleopatra, and Hernandia cordigera, together with species of the Proteaceae genera Kermadecia, Macadamia, and Sleumerodendron.

The Montane rain forests are also mixed-species, predominantly the conifers Araucaria, Agathis, Podocarpus, Dacrydium, Libocedrus, and Acmopyle, and the angiosperms Metrosideros, Pterophylla, Quintinia, and Nothofagus.

The ultramafic rocks, which formed in the deep ocean, are rich in metals, including nickel, magnesium, chromium, and manganese, which are toxic to many plants.