Niue is a very small island in the large southern Pacific Ocean. Ocean surface currents flow mostly with the trade winds in a north-westerly direction, arriving from a cooler area of the Pacific without neighbouring islands. But occasionally a reversal happens. During such instances, larvae or mature animals from neighbouring islands to the north may arrive at Niue. The gene pool in Niue is thus periodically updated, preventing unique endemic species to evolve here. Thus Niue is not likely to play a role in the world's biodiversity and it is unlikely to find species here that are found nowhere else in the world.

When species arrive in Niue's coastal seas, they are subjected to the following deselecting influences:

• temperature: the seas around Niue are cool for the tropics, as cool water arrives from the south-east. It limits growth and deselects species unable to cope with these temperatures. Thus many species from warmer waters are unsuccessful in establishing themselves at Niue.
• small area: Niue has very little hard shore, the place where most marine organisms are found. So there is precious little room for large numbers of each species. This has serious consequences and deselects those species unable to cope in small numbers on small territories.
• poverty: the clear blue water contains very little food. Energetic and wasteful species such as sardines cannot possibly live here. It deselects the energetic and wasteful species while selecting for frugal ones who also expend little energy by being 'lazy'.
• isolation: on the one hand Niue is insufficiently isolated to produce its own endemic species, but on the other hand is sufficiently isolated in a large desert ocean to cause persistent recruitment failure. This has selected for animals that grow old or care for their brood or have some other strategy to cope.
• hurricanes: hurricanes bring large and deep waves that destroy the shores in their path. The sheer speed of the water when it shears over the shore is enough to water blast all soft life to death, and the rubble in its path scours coral structures to their basic shapes. Although large hurricanes are very infrequent, they nonetheless have a prominent and lasting effect on the northward shores of Niue which they lay barren, to be grazed by tangs and urchins.
• trade winds: the opposing side of Niue is constantly buffeted by a swell which has an equally important influence on the life below and the shape of the coral slope. It creates shallow barrens as it is not strong enough to create deep ones.
• exploitation: on land the natural species have been exploited in many ways, and the sea has always been fished. The coralline reef flats have particularly been harvested intensively.

On land, nature has very similar influences. Sea birds for instance are too wasteful (energy-spending) to survive here because they depend on rich sea life in the sea around Niue. On land we can recognise the following selective factors:

• isolation: Niue is sufficiently isolated for most forms of life by the 500km of ocean between it and the nearest islands. But birds, bats and plant seeds can be brought there by cyclonic winds. People found it only some 1500 years ago. The plant and animal communities on Niue are thus not easily disturbed by natural newcomers.
• small size: Niue's land surface (260km2) is very much larger than its rocky shore (4km2) but even so, this is insufficient to maintain the biodiversity of a tropical rain forest. Furthermore, Niue has four distinct habitat zones extending from the reef flats towards its centre.
• moisture/rainfall: Niue receives about 2m of rainfall, about twice that of Auckland, New Zealand. But the soils cannot retain it as it seeps quickly down into a labyrinth of channels eventually leading to the sea. Niue has no creeks or rivers, no springs no wetlands.
• droughts: Niue has a wet and a dry season but occasionally two or more successive years of drought, which upsets life on the island considerably.
• winds: steady trade winds of 15-25 knots (25-45km/h) blow from the southeast for most of the year. In the months with the warmest water in the tropics (Nov-Jan) a tropical cyclone may descend on Niue with variable strength. It brings very strong winds (120-300km/h) capable of stripping leaves from branches, felling trees and blowing insects and birds off the island. Powerful cyclones like Heta leave a lasting influence.
• soil: Niue does not have volcanic rock or soil. It consists of a coral limestone rock extending at least 100 metres under water and 70 above. Niue's soils were formed in a very slow process by the weathering of coral rock under a canopy of vegetation. Where forest trees stand, the soil is deepest and in the coastal saltspray zone shallowest.

• selecting useful species: everywhere in the world, already in their nomadic stage, people have knowingly and unknowingly promoted the species of use to them.
• by clearing competing species around them
• by collecting fruits and seeds and spreading these around
• by defecating in the areas of productive species and thereby fertilising them
• introducing wanted species: when settling on a new island, people brought important food crops with them such as the taro root. Edible and ornamental species were also traded between islands.
• introducing unwanted species: wherever people went, they took with them unwanted species such as flies, rats and weeds. Also on Niue chickens went wild.
• introducing noxious species: often wanted food species spread, upsetting the natural environment. cats, chickens and pigs have caused much damage. It is feared that the introduction of honey bees has been detrimental to the population of colourful parakeets who also depend on honey for sustenance.
• habitat change: in order to suit the environment to their needs, people have always made habitat changes for dwelling, cultivation, roading, fortification and so on. With the aid of fossil fuel this could be done on a grand scale. In Niue most of the land has been changed but some natural areas remain.
• slash-and-burn: slashing the new growth and burning it has always been part of shifting agriculture, Niue's predominant way of cultivation, but arrowroot (an important source of starch) was always the first to emerge after burning. When the traders expressed interest in arrowroot, wildfires became a new way of life, encouraging the regrowth of arrowroot. As we now know, this had a disastrous effect on the soil's quality as valuable nutrients also went up in smoke.
• exploitation: in addition to habitat change for cultivation, people exploited the natural world by hunting. On Niue the most important hunted animal species are: fruit bats, coconut crabs and birds. Many plant species are exploited, particularly for housing, canoes, weaving, food and more.
• emigration: with Niue's population steady at 4000-5000, the locals were living within ecological boundaries, exerting a high pressure on the environment. But after World War Two most left for better pastures in New Zealand and Australia. At the turn of the millennium, 20,000 Niueans were living in Acukland, leaving about 1000 to mind the island. This significant emigration has relieved the pressure on resources, giving both the land and nature respite.

habitat zoning on land The diagram shown here simplifies the natural habitat zoning on Niue, both above and under water. It shows a cross-section from roughly SE to NW such that the hurricane side is on the left side and the trade wind side on right. From left to right the following habitat zones can be distinguished:

• Alofi underwater barrens: occasional tropical cyclones destroy coral life, resulting in a barren seascape to 70m depth, which is kept barren by incessant grazing of sea urchins, surgeonfish and parrotfish.
• Alofi reef flats: coralline reef flats just above low tide level, heavily exploited by the practice of reef gleaning and collecting. During high tide this area is heavily grazed by surgeonfish.
• Alofi terrace wind-struck rain forest: hurricane winds cause a heavy toll on the natural rain forest. This habitat has also been modified for living.
• Mutalau ridge rain forest: a remnant of the original rain forest, not suitable for cultivation.
• Fern lands: clearfelled rainforest and soils cultivated for food, resulting in fern lands.
• Huvalu rain forest: a central lagoon remnant of the original rain forest. The remaining area of Huvalu high forest is estimated at 6000 acres (2400ha) with a tapu area of 40 acres (16ha) within, now protected for four generations.
• Mutalau ridge rain forest: as above but this side adjoins to the unmodified saltspray vegetation, a haven for the coconut crab.
• Saltspray karrenfeld and vegetation: because the rainforest never stood here, soils are poorly developed leaving an inaccessible terrain of sharp coral pinnacles and sink holes (karrenfeld) with low vegetation, dominated by salt-tolerant shrubs such as Pandanus mangrove trees.
• High pools: as the trade wind swell bursts skyward, it deposits water on ever growing deep rock pools, the mysterious high pools with their own miniature ecosystems.
• Trade wind barrens: the trade swell is not powerful enough to create deep barrens but only a short ledge and step. This shore shape breaks the swell by bursting it skyward and bouncing it back to sea.
• The tradewind coral slope: a gradual slope of healthy corals with rapid water movement down to 20m. Although corals thrive, fish dislike the continuous water movement.

This map shows the actual location of Niue's vegetation types. It distinguishes two zones, the coastal zone and the inland area. The coastal zone covers the salt spray zone, the coastal forest and coastal fernlands. The inland area covers regenerating forests and fernlands and the high rain forest. As one can see, the amount of original vegetation is not large but relatively larger than that in New Zealand. The Huvalu Forest Park covers both regenerating and original forest and may take several centuries to regenerate fully. Click here for a larger version of this map: niue11m.gif.

f044601: the Alofi underwater barrens are created by large storms and maintained by a large variety of grazers.

f044913: small black needle urchins inside their sockets waiting for the night to emerge when they graze their gardens.

f220937: the coralline reef flats found mainly on the Alofi side of the island. f223011: reef gleaning for sustenance is still widely practised. The coralline reef flats do not consist of corals but coralline algae, covered in a sum of brown-green slimy algae. Mysterious rock pools break the surface.

f222925: the Alofi terrace is frequently hit by hurricanes, low, salt-resistant shrubs survive.

0507008: on the hurricane side, tall trees are occasionally stripped, which selects for the most suitable types.

f221229: where good soils are found, people strip the vegetation for cultivating taro crops. Here the fields are left fallow to recover.

f220516: a prosperous taro crop.

0507450: the author and Misa by a tall forest tree with buttress root stabilising it against hurricane winds.

0507451: tall forest trees are still found in the Huvalu rain forest.

0507470: the fou tree (Hibiscus ) was used for making fire.

0507140: coconut palms grow all over the island but are promoted near settlements and on soils unsuitable for farming.

f223222: the coastal rain forest grows where jagged rocks prevent cultivation.

f220816: pandanus mangrove trees are salt-resistant and thrive in the saltspray zone.

f220733: salt spray from incessant large swell has created a moon landscape of very sharp jagged rocks with salt resistant vegetation.

f223220: a salt-resistant perennial weed grows where no other can.

f220503: the swell is thrown high skyward, causing copious amounts of salt spray (Anaana Point).

f044715: underwater on the tradewind side extends a slope of healthy corals. The large giant clam seen here enjoys de-facto protection by the waves.