A third of New Caledonia is covered by ultramafic massifs (very poor in silica) with an omnipresence of iron (50% and more), a low nutrient content and an excess of magnesium. It shows a high concentration of heavy metals which become toxic with a climate changing from hot to humid periods. During 32 million years, however, a great floristic diversity acclimatized, 70% of which are endemic.