Hoar frost on the vines at Akarua’s Cairnmuir Road vineyard in Central Otago.
Akarua Winery, Central Otago rock-crushing machines alter the soil profile and even the subsoil to make areas freer draining and easier to work.
Environmental learning in the dispersion of the vine
It is tempting to interpret the dispersion of the vine in New Zealand in the second half of the twentieth century solely through the soils and climates of the evolving regions. At a macro scale, several aspects of the New Zealand climate, soils and relief are pertinent. Both islands are characterised by strong west to east gradients in rainfall, but their intensity varies with local conditions and at various resolutions. Their pattern is more straightforward and intense in the South Island where the Southern Alps are responsible for a marked rain-shadow effect and rainfall gradient from west to east. In less than 100 kilometres between the Alps and Central Otago, annual precipitation falls from several metres to under 300 millimetres – a figure less than half that of the prestigious grape-growing areas of France such as Burgundy and Bordeaux.
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In the North Island the patterns are more complex because two or three ranges of hills or mountains usually intervene from west to east to provide successive rain shadows and slight ‘continental’ effects. Waiheke Island, Hawke’s Bay and the Wairarapa all receive lower rainfall than areas to the west of them. The last two have annual precipitations of under 1000 millimetres, while much of Canterbury receives under 750 millimetres. Gisborne receives higher annual rainfall partly because in some seasons it is influenced by remnant tropical cyclones in the late summer months.
In very broad terms, we have seen the dispersal of the vine to regions where climatic conditions are more favourable – regions with lower precipitation in the crucial parts of the growing season, higher daily temperatures after veraison, and higher sunshine hours during the ripening period. The southern regions have greater risk from late-spring frosts and the possibility that in some seasons it will be difficult, maybe even impossible, to ripen grapes to a level to make still wines of real quality. If that happens, all of these southern regions at least have the possibility of directing their Chardonnay and Pinot Noir grapes to sparkling wines, where the level of sugar at harvest is not so demanding. Soils of the expanding regions are generally free draining, with Gisborne an obvious partial exception.
Yet such simple spatial association of natural environment with activity belies the role of people in the process and a host of micro-effects. Consider the complexity of the relationship between weather and varieties of Vitis vinifera. Like the prestigious regions of France, all of New Zealand is close to the polar limit for ripening many varieties of grapes. The problem of weather variability is better expressed in probabilistic terms. Empirical experience over many seasons is required before it is clear whether a variety will ripen to a satisfactory balance of sugar and acidity in a sufficient number of years to produce grapes with the flavour characteristics to make wines of real quality. In a sense, grape growing for wine is not about finding sites with the ‘ideal’ climates but about finding sites where the probability of a sufficient number of outstanding years, or very good, or even good years is high. In addition, the probability of ‘wipeouts’ – from late-spring frosts, or rampant fungal diseases from regular rain and high humidity after veraison – must be low. The task of the wine enterprise is to make outstanding wine out of the best seasons and the best possible wine from the worst seasons.
Moreover, any analysis of the weather record needs to be made for specific varieties, or indeed different clones each with their own phenology. Each variety (or clone) has bud burst at a different time, flowers at a different time, undergoes veraison at a different time and reaches physiological ripeness at a different time. And each event in this phenological sequence influences the next. The weather of any single year also affects the vine’s performance in the following year, notably in the fertility of the buds. Yield, one of the key variables that the viticulturist is trying to influence, is affected. The weather sequences of particular years are seldom if ever exactly repeated in another. And the viticulturist/winemaker has only 40 or so vintages in which to perfect their art, or 80 or so if blessed with the constitution to be a flying winemaker between the southern and northern hemispheres into their sixties. Herein lies the joy and frustration of growing grapes and making wine.