New Caledonia: Wandering islands lost in time

New Caledonia has a higher proportion of endemic species than almost anywhere on the planet, Dr Shane Wright told the Whanganui Science Forum.FRANK GIBSON was among those learning about the country's 3300 plant species.

Dr Shane Wright, of Auckland University, painted a picture of the ecology of New Caledonia that had positives and negatives.

Closed canopy forest is hard to find in New Caledonia below 500m because so much has been lost to fires and mining.

At first look, New Caledonian and New Zealand forests look very similar, but they are profoundly different. New Caledonia represents New Zealand as it might have been before the ice ages. New Caledonia has enormous diversity in a relatively small area.

They are not too distant from each other, but they have different geological life stories. 80 million years ago Aotearoa was connected to the continent of Antarctica while Kanaka (indigenous name for New Caledonia) has roamed the surface of the earth on the coat tails of Australasia.

As they have drifted, the two groups of islands have taken their populations of animal and plant life with them, keeping them largely isolated from the rest of the world.
This isolation has allowed the flora and fauna of both land masses to evolve in ways that could not happen elsewhere.

Until it was wiped out by humans, Aotearoa had the moa. Until the arrival of humans New Caledonia had the sylviornis.

This giant bird (1.7 metres tall and weighing about 30kg) was hunted to extinction by the Lapita people, who are the ancestors of the Kanak.

The bird was probably a slow-moving browser and is still referred to in Kanak oral history as the "du". Originally thought to be a relative of the moa but has now been shown to be a very ancient, separate species.

New Caledonia had its own species of crocodile – the Mekosuchus,which again disappeared not long after humans arrived.

Unlike what you think of as a crocodile the Mekosuchus did not live in water. Because of the poor soils there was no large ground-dwelling prey, causing the Mekosuchus to evolve specialised back teeth for cracking mollusc shells.

Australasia and Antarctica split about 35 million years ago. The difference in their paths has had a profound difference on the way their plants and animals have evolved. New Caledonia has stayed in the tropics while New Zealand has been repeatedly affected by ice age climates.

Although mountainous, all of New Caledonia is below whatwe in New Zealand would call the tree line, so there has been no glaciation in New Caledonia. The result is that although New Caledonia has only about one 15th the land area of New Zealand it has about 50 per cent more plants that survive nowhere else.

Severe ice age weather has stunted the ability of New Zealand to evolve its diversity.
The plants in New Caledonia initially came mainly from the Paleotropics, which encompass South East Asia and Africa northward from the Cape to the northern edge of the Sahara. New Zealand also had this sort of diversity originating in the tropics until the ice ages started about 2.5 million years ago. New Zealand has been through profound cold at roughly regular intervals of 100,000 years.

This cold has removed the kapoks, coconuts and cinnamons that came from the Paleotropics and would have been seen in the New Zealand landscape before the ice ages. This is one of the many important qualities of New Caledonian plant life.

It is a repository of many forms of plant life that have disappeared elsewhere. As an example, there are about 700 species of gymnosperm (cone-bearing plants) worldwide. Of these 44 are found on New Caledonia, making it the most diverse area for gymnosperms in the world. About 75 per cent of species found on New Caledonia are found nowhere else.

This diversity is spread through 3 biomes (communities of plant and animal life). These are tropical rain forest, tropical dry forest and maquis. The soils of the maquis areas have an interesting history.

Earthquake activity in New Zealand is caused by the Pacific Plate moving towards and diving under the Australian Plate.

In New Caledonia movement of tectonic plates has forced a layer of igneous rock to ride over the neighbouring plate to an original depth of about 2000 metres. Much of this has been lost to erosion in the past 30,000,000 years but what is left makes New Caledonia a valuable prize.

This overlying rock has very low levels of nitrogen, phosphorus and potassium.
As any farmer will tell you this means the soils formed from these rocks will be very unfertile. It also has very high levels of iron, magnesium, nickel, chromium, cobalt and manganese. As any chemist will tell you this means there are fortunes to be dug out of the ground and mining of these metals is the mainstay of the island's economy.

Maquis consist of plants that have evolved to be able to survive in highly toxic soils.
Over 90 per cent of plants in maquis country occur nowhere else in the world. This means that there are some totally unique forms of evolution going on in these areas.
Plants in maquis country rarely grow beyond shoulder height. This is due to the extreme toxicity of the soil arising from the high levels of chromium and cobalt.

A tree may look like a sapling but be 400 years old. Its growth has been stunted by the toxic soil. Maquis country looks like land in New Zealand that is coming back into growth after being clear-felled. But this is the mature state for maquis.

Some of the maquis plants are hyperaccumulators. This means they not only grow in these toxic soils, but they take up high concentrations of the metals without harm to the point where the plant sap is blue due to the high concentration of nickel. When dried the sap of some hyperaccumulators has been found to contain 25 per cent nickel.

Possibly the most important aspect of the plant life of New Caledonia is that it is a refuge for species that have become extinct in other places. This alone is enough to make its preservation important.

*Frank Gibson is a semi-retired teacher of mathematics and physics who has lived in the Whanganui region since 1989.

Frank Gibson is a semi-retired teacher of mathematics and physics who has lived in the Whanganui region since 1989.