Biodiversity of New Caledonia - Evolution and History

Evolution and History

The species of the archipelago of New Caledonia are relicts of a type of vegetation which earlier covered much of the tropics of the Earth, including much of the mainland of Australia, South America, Antarctica, South Africa, North America. Although tropical cloud forests disappeared during the glaciations, they re-colonized large areas during successive geological eras when the weather was favorable again. At other times they were replaced by more cold-tolerant or drought-tolerant sclerophyll plant communities. Many of the then existing species became extinct because they could not cross the barriers posed by new oceans, mountains and deserts, but others found refuge as species relict in coastal areas and Islands.

When the large landmasses became drier and with a harsher climate, this type of forest was reduced to those boundaries areas. Although some remnants of archaic rich flora still persisted in their coastal mountains and shelter sites, their biodiversity were reduced. The location of the New Caledonian Islands in the Pacific Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate which has allowed these communities to persist to the present day.

The ecological requirements of many of the species, are those of the laurel forest and like most of their counterparts laurifolia in the world, they are vigorous species with a great ability to populate the habitat that is conducive. The geographical isolation and special edaphic conditions helped to preserve it too. Some species are even specialized in nickel hyperaccumulation such as the Sapotaceae Sebertia acuminata.

Some geologists assert that, as the island moved north due to the effects of continental drift, it submerged at various intervals, extinguishing its terrestrial flora and fauna. Botanists counter that some areas must have remained above sea-level, serving as refugia. Many members of the late Cretaceous - early Tertiary Gondwanan flora survived in New Caledonia's equable climate but were eliminated in Australia due to increasingly dry conditions. The isolation of New Caledonia was not absolute, given the rise and fall of sea level caused by the ebb and flow of ice ages. Land bridges or islands formed between New Caledonia and its neighbours, the Solomon Islands, Vanuatu, and Australia. Thus new species came to New Caledonia while Gondwanan species were able to penetrate the Pacific Islands region. Plants have limited seed dispersal mobility away from the parent plant and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors.