New Zealand’s soils are often deeply weathered, lacking in many nutrients, and, most of all, highly variable over short distances. Soils based on sedimentary rock formations are mostly clays and are found over about three-fourths of the country. Pockets of fertile alluvial soil in river basins or along river terraces form the orchard and market-gardening regions of the country.

In the South Island, variations in mean annual precipitation have had an important effect. The brown-gray soils of Central Otago are thin and coarse-textured and have subsoil accumulations of lime, whereas the yellow-gray earths of much of the Canterbury Plains, as well as areas of lower rainfall in the North Island, are partially podzolized (layered), with a gray upper horizon. The yellow-brown soils that characterize much of the North Island are often podzolized from acid leaching in humid forest environments. Their fertility varies with the species composition of their vegetation. Forests of false beech (genus Nothofagus), as well as of tawa and taraire, indicate soils of reasonably high fertility, while forests of kauri pine and rimu indicate podzolized soils.

Climate

New Zealand’s climate is determined by its latitude, its isolation, and its physical characteristics. There are few temperature extremes.

A procession of high-pressure systems (anticyclones) separated by middle-latitude cyclones and fronts cross New Zealand from west to east year-round. Characteristic is the sequence of a few days of fine weather and clear skies separated by days with unsettled weather and often heavy rain. In summer (December–February), subtropical highs are dominant, bringing protracted spells of fine weather and intense sunshine. In winter (June–August), middle-latitude lows and active fronts increase the blustery wet conditions, although short spells of clear skies also occur. Because of the high mountain chains that lie across the path of the prevailing winds, the contrast in climate from west to east is sharper than that from north to south. Mountain ranges are also responsible for the semicontinental climate of Central Otago.

Changes in elevation make for an intricate pattern of temperature variations, especially on the South Island, but some generalizations for conditions at sea level can be made. The average seasonal and diurnal temperature range is about 18 °F (10 °C). Variation in mean monthly temperature from north to south is about 10 °F (6 °C). In most parts of the country, daytime highs in summer are above 70 °F (21 °C), occasionally exceeding 80 °F (27 °C) in the north, while winter daytime highs throughout the country are rarely below 50 °F (10 °C).

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Precipitation is highest in areas dominated by mountains exposed to the prevailing westerly and northwesterly winds. Although mean annual rainfall ranges from an arid 12 inches (300 mm) in Central Otago to as much as 250 inches (6,400 mm) in the Southern Alps/Kā Tiritiri o te Moana, for the whole country it is typical of temperate-zone countries—25–60 inches (635–1,520 mm), usually spread reliably throughout the year. Snow is common only in mountainous regions, but frost is frequent in inland valleys in winter. Humidity ranges from 70 to 80 percent on the coast and is generally 10 percent lower inland. In the lee of the Southern Alps/Kā Tiritiri o te Moana, where the effect of the foehn (a warm dry wind of leeward mountain slopes) is marked, humidity can become very low.

Climate change in the 21st century is expected to affect temperature and precipitation patterns in New Zealand, although those changes are expected to be more moderate compared with global changes. Under moderate and high carbon emission scenarios, climate models predict that the North Island will bear the most significant changes in average temperature, an increase of 2–4 °C (3.6–7.2 °F), whereas the South Island is expected to receive greater amounts of winter rainfall.

Plant and animal life

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The indigenous vegetation of New Zealand consisted of mixed evergreen forest covering perhaps two-thirds of the total land area. The islands’ prolonged isolation encouraged the evolution of species unknown to the rest of the world; almost nine-tenths of the indigenous plants are peculiar to the country. Today dense “bush” survives only in areas unsuitable for settlement and in parks and reserves. On the west coast of the South Island, this mixed forest still yields most of the native timber used by industry. Along the mountain chain running the length of the country, the false beech is the predominant forest tree.

European settlement made such inroads on the natural forest that erosion in high-country areas became a serious problem. Various government agencies were established to manage and conserve forests, beginning in the late 19th century, and a state forest service was established in 1921 to repair the damage; it uses forest-management techniques and does reforestation, using exotic trees. Experimental areas on the Volcanic Plateau were planted with radiata pine, an introduction from California. This conifer has adapted to New Zealand conditions so well that it is now the staple plantation tree, growing to maturity in 25 years and having a high rate of natural regeneration. Large areas of the Volcanic Plateau, together with other marginal or subagricultural land north of Auckland and near Nelson, in the South Island, are now planted with this species.

European broad-leaved species are widely used ornamentally, and willows and poplars are frequently planted to help prevent erosion on hillsides. Gorse has acclimated so readily that it has become a menace, spreading over good and bad land alike, its only virtue being as a nursery for regenerating bush.

Because of New Zealand’s isolation, when the Māori arrived in the 13th century, they found few animals. There were three kinds of reptiles—skinks, geckos, and tuatara, the latter “beak-headed” reptiles having been extinct elsewhere for 100 million years—and also a few primitive species of frogs and two species of bats. These are all extant, although they are confined primarily to outlying islands and isolated or protected parts of the country.

In addition to their domestic animals, Europeans also brought other species with them. Red deer, introduced for sport hunting, and the Australian opossums (for skins) have multiplied dramatically and have greatly damaged the vegetation of the high-country bush. The control of goats, deer, opossums, and rabbits—even in the national parks—is a continuing problem.

In the absence of predatory animals, New Zealand is a paradise for birds, the most interesting of which are flightless. These originally included several species of moa, a large bird that was eventually exterminated by the Māori. The kiwi, another flightless species, is extant, though only in secluded bush areas. Wekas and takahes (barely rescued from extinction) probably became flightless after their ancestors’ arrival on the islands millions of years ago. The pukeko, a swamp hen related to the weka, moves primarily by walking and swimming; though it can fly, it does so only with great effort. Some birds, such as saddlebacks, are peculiar to New Zealand, but many others (e.g., tuis, fantails, and bellbirds) are closely related to Australian birds. Birds that breed in or near New Zealand include the Australian (Australasian) gannets, skuas, penguins, shags, and royal albatrosses.

Because New Zealand lies at the meeting place of warm and cool ocean currents, a great variety of fish is found in its surrounding waters. Tropical species such as tuna, marlin, and some sharks are attracted by the warm currents, which are locally populated by snapper, trevally, and kahawai. The Antarctic cold currents, on the other hand, bring blue and red cod and hakes, while some fish (such as tarakihi, grouper, and bass) that can tolerate a considerable range of water temperatures are found in the waters all around the coasts. Flounder and sole abound on tidal mudflats, and crayfish are prolific in rocky areas off the coastline.