volcano erodes or the local ocean bottom subsides. If coral growth can keep up with the speed of this process, a barrier reef (C) is formed on the base of coral limestone; note the wider, locally deeper lagoon.
Ultimately, all land will be eroded, and the barrier reef will become an atoll (D) en-closing an open lagoon. The process from A to D can take 30 million years.
It is possible that an atoll can be uplifted by movements in the earth’s crust, by which an uplifted coral island is formed. A limestone rock emerges (E) and becomes encircled by a fringing reef.
LAND USE AND VEGETATION TYPES Once most islands were mainly covered by forest. The arrival of man brought about many changes in this environment and the following are the main present-day habitats.
Ocean
Open Tropical Ocean: warm water contains less prey (fish, squid, etc.) than cold water, therefore most seabirds in the tropical ocean are more numerous at places where deep cold currents from higher latitudes well up above (under) sea mounts (submerged volcanoes) and at the western edges of the Pacific.
Temperate Ocean: water temperatures between 10 and 18°C, found between the tropics and 48°S and N. Rich in oxygen and nutrients, very rich in fish (less species than in tropical seas, but often in large shoals) and in other life forms.
Coastal habitats
Lagoon: shallow, clear water rich in food for terns, gulls, noddies, tropicbirds and frigatebirds.
Seashore: especially important for migrating shorebirds.
Mangrove: mangrove stands support many bird species and form a habitat where heronries are often found.
Littoral Forest: the forests and thickets bordering the beach.
Lowland forest types
Lowland Dry Forest: found at the dry north-western side of high mountain chains, where the rain, brought in by the eastern trade winds, is released on the eastern slopes. All forms of dry forest are almost completely transformed to agricultural use. In the mixed exotic/native remains a few of the original endemic bird species may be found, plus many alien species.
Lowland Rainforest: as highland rainforest but with a more diverse range of tree species, denser undergrowth and many tree ferns.
Agricultural habitats
Coconut/Breadfruit Forest: found in the coastal areas of many Pacific islands. Mixed with species such as guavas, mango and Ficus. This is an ancient man-made habitat.
Farmland: food crops, fruit orchards, floriculture, vanilla, etc.
Savanna: low production grassland with some tree cover, many breadfruit shrubs and dominated by exotic grasses. Often replaces (dry) forest after repeated burning.
Grassland: areas dominated by grasses with little tree and shrub cover, also replacing former forest. Savanna and grassland in Pacific islands are normally the result of human activity.
Wetlands
Wetlands: rare freshwater habitat in the Pacific; most original wetland is drained and changed to crop- and grassland. Wetland bird species are now dependent on man-made ponds, reservoirs, sewage fields, etc.
Upland forest types
Production Forest: mainly Caribbean Pine or Eucalyptus plantations.
Upland Dry Forest: once covered about one-third of the lar-ger Fijian islands and also was common at the leeside of the Hawaiian islands; now greatly altered to savanna with sparse vegetation.
Montane Rainforest: various forest types united by high humidity and limited temperature variations. Exact timing of dry season varies. Characterised by epiphytes and mosses. This habitat has often disappeared from the smaller islands and the remains on larger islands are threatened.
Cloud Forest: the highest parts of rainforest, which are characterised by a high incidence of fog.
Secondary Forest: new natural forest where the original forest has disappeared. As a habitat it is highly variable, from low woodland to tall forest with more open canopy than virgin forests and lacking old emergent trees.
Other habitat types
Lava Plains and other bare ground at high altitudes: for some bird species this forms an important habitat (Hawaii Goose, Omao, Tahiti Petrel, White-tailed Tropicbird).
Some Basics for New Zealand
GEOLOGY The core of New Zealand was pushed, compressed and folded up against the Australian area some 370 million years ago. About 300 million years later (or 70 million years ago) New Zealand and Australia were separated along a rift that created the Tasman Sea. The rift ‘healed’ and 25 million years ago the eroded and flattened remains started to be uplifted again.
South Island is dominated by a row of Alps over the full western length. The subduction processes in the trenches north and south of South Island are contrary to each other, pressing the alpine area together. Along the main Alpine Fault both ‘Alp-halves’ are sliding along each other (the western ‘half’ moving faster north). Secondary faults are forming the highlands near Kaikoura. This is also the place where the deep Kermadec Trench brings cold, fish-rich water near the coast, attracting a host of seabirds.
North Island is dominated by volcanic activity. The Pacific Plate dives under the Australian Plate that carries the island. Where the plate sinks into the liquid-hot asthenosphere, magma is released and ‘floats’ to the surface forming an arc of volcanoes in the Taupo Volcanic Zone. In this zone and elsewhere there are several lakes in places where once large to very large magma chambers exploded (each one forming a ‘caldera’), after which the remains collapsed and were filled by rain water. It is also the zone where many hot springs are found; the water that surfaces here (often as steam) is heated deeper down in the earth’s crust. The volcanoes and calderas outside the Taupo Volcanic zone are mainly remnants of older volcanic arcs.
LAND USE AND VEGETATION TYPES Originally the greater part of New Zealand was covered by forest. After the arrival of the Polynesians (ad1000) and later on the settlement of the Europeans (from about ad1840) more than 50% of the forest was cleared, mainly by fire and grazing. Origin-ally there were no mammals in New Zealand except seals and three bat species, but when the first people
