The map of Quaternary sediments is a surrogate for aspects of the surface materials that shaped the terrain of many wine regions and were gradually transformed into soils. In both islands almost all vines are grown on these Quaternary sediments. They were mainly deposited in the last million years, beginning during the most recent ice ages. In the South Island the soils were shaped by terrestrial deposition of materials eroded mainly from the Southern Alps and subsidiary ranges by glaciers and rivers. These deposits formed the Canterbury Plains, the largest area of gently sloping land in the country, as well as smaller plains like the Waimea and Wairau in Nelson and Marlborough respectively. Similar work by glaciers and rivers over time formed the valleys and terraces of Central Otago.
In the eastern lower North Island, from Hawke’s Bay to the Wairarapa, the sediments are mainly marine in origin, including limestone, siltstone and sandstone. In both islands these Quaternary sediments have since been transformed by both the erosion and the deposition from the major rivers draining them. Much of their terrain now consists of gently sloping terraces and former flood plains, often with gravelly soils that can be hundreds of metres deep.
Map Of Wellington New Zealand Photo Gallery
When these two criteria – precipitation under 1000 millimetres and the Quaternary sediments – are combined, large areas of land are filtered out. In the North Island, the fine alluvial soils of the Hauraki Plains and Waikato, and the volcanic and alluvial soils of Taranaki and the Manawatu, do not meet both criteria. Nor do the alluvial soils of the West Coast and Southland in the South Island. The competitive advantage of these regions, partly derived from the higher rainfall and soils of higher natural fertility, sees them practising intensive grassland farming, mainly dairying and fattening sheep and cattle and growing various crops. The vine does not get a look in and nor should it.
Three maps of New Zealand unravel the calculation of ‘mean temperature of the warmest month’ that was used by Prescott (Figure 4.5). It is quickly apparent from this group of climate stations in wine regions that the pattern of maximum temperatures is very similar across the North and South Islands. The continental effect of the Southern Alps and associated ranges explains these higher temperatures at more southern latitudes in the interior and towards the east coast of the South Island. Lower minimum temperatures at night decrease the mean temperatures in the South Island. If these minima were higher in the South Island (more similar to the North Island), several parts of it would see even the 19°C isotherm appearing. It seems, on the surface, that the heat accumulation must be greater than shown by this measure and is partly explained by day length. Various scientists have included day length and other variables to improve such measures. Nevertheless, the best evidence that the climate is suitable is the performance of the varieties of vines being grown.
Another measure of temperature – number of days during the year with temperatures over 25°C – identifies very effectively the major localities growing vines (Figure 4.6). It also demonstrates that the conditions during the daylight hours, when the vine is actively photosynthesising, are the most important for achieving physiologically ripe grapes. Leaving aside the humid Hauraki Plains and Waikato, where intensive pastoral farming on fine alluvial soils takes first choice of the land, the temperature map identifies the main localities where viticulture is currently concentrated. In the North Island these are the Gisborne Plain and adjacent land along the coast including Tolaga Bay, the coastal plains and river terraces around the bight of Hawke Bay, and part of the Wairarapa. In the South Island, conditions for viticulture are concentrated on the Wairau Plain, a broad strip of the eastern area of Canterbury from inland and north of Waipara to mid-Canterbury, and the plains of the Mackenzie country and Central Otago. These last two localities are the ‘continental’ part of the South Island because the protection of the highest parts of the Southern Alps to their west modifies their climates to make them resemble those of the interior of continents.
The descending air masses on the leeward side of the mountain ranges are also responsible for the nor’westers of the Canterbury Plains (Fohn winds) that dry as they descend and suck the moisture from the soil and plants, making irrigation essential for grapes to thrive in these desiccating conditions. Although much of the Canterbury
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