THE WIND AND THE RAIN

Korero (AEWS), Volume 3, Issue 9, 4 June 1945, Page 16

THE WIND AND THE RAIN

From a Report by

New Zealand’s soil erosion problem has two outstanding characteristics first, its seriousness and extent, and, second, the different forms it takes in different regions. Soil erosion is extensive, especially when you consider how small New Zealand is, and serious when you consider how short a time Europeans have been here. It becomes still more serious though, when you remember that the national economy and high living standards of New Zealand’s million and three-quarter people both depend almost entirely on a restricted range of exports — all derived immediately from the soil. Four years’ reconnaissance study of the wasteful use of our soil shows above all, that soil erosion is a distinct and separate problem in different areas, each area demanding its own solution. In spite of the small total area of New Zealand, conservation must be set about regionally and the cultural and physical conditions which have hastened erosion must be thoroughly understood. Natural geologic erosion in New Zealand is more

rapid than in older countries. Geologically, the earth’s crust that forms New Zealand is of recent origin, which means that it is sharply elevated, and high elevation and small area mean steep run-off. This, with climates which actively help erosion, has made the structure of the country even more prominent. You will have noticed how most of our landscape is made up of steep, deeply-bitten hill faces, and abrupt and ever-changing breaks of slopes. Climate ordinarily wears away the land. But if Nature is left to itself an uneasy balance is maintained. With the appearance of man this delicate balance is upset and climate ranges itself alongside him as chief collaborator. It is different climates and different elements of climates that to a great degree determine the rate and kind of accelerated erosion. Twelve month extremes of temperature don’t matter nearly so much as daily temperature variations, which in New Zealand are considerable. In easterly districts generally and the South Island interior

p articularly, these variations are abnormally large and become important when they frequently involve moisture in the top soil. The annual frequency of ground frosts is a fair, if not accurate, measure of the effects of these variations. In some regions as many as two hundred ground frosts a year may be expected to assist in the slow forms of mass-movement brought about in the first place by burning and grazing and pastoral settlement. By far the greater part of New Zealand has a heavy rainfall, though generally it is evenly distributed through the year. Five-sixths of the total area has average annual totals of over 40 in., and of this almost 75 per cent, has 60 in. Totals of 200 in. are frequent. In some parts, notably North Auckland, Poverty Bay, parts of Hawke’s Bay, and the northeastern tip of the South Island, more than 30 per cent, of the annual fall is concentrated in the three winter months. Rainfall variations affect the variations in soil moisture content; but it is the intensity of New Zealand’s heavy rains (particularly those recorded periodically over two-, three-, and four-day periods) that increases the severity of our soil erosion problem. The New Zealand area, too, is exceptionally windy, but, despite the heavy rainfall, very sunny. Moreover, on the sheltered side of the ranges warm, dry winds, low humidity, and high evaporation go with lighter rainfall and as much as 2,400 to 2,500 sunshine hours. Such climatic characteristics occur in areas where the delicately adjusted grassland of the plains has suffered because of cultural malpractices. Such areas— Marlborough, Canterbury, Central Otago, and the Mackenzie Country—face high erosion hazards. The vegetation of New Zealand was adapted to the soil, the climate, and the contours of the country, and the soil was held. However, the conversion of New Zealand from swamp, forest, or virgin grassland to one huge farm with pastures chiefly of introduced grasses has been ruthless. The extent and speed of the change have been astounding; but largely because of haste and ruthlessness and the extent to which the process has been carried in such short time, the

value of the land has changed—for better in some places, for worse in others. In New Zealand, as elsewhere, unconsidered interference with natural vegetation is a prime cause of unnecessary soil decay. Interference has been direct and indirect. Drainage and reclamation, ploughing virgin sod, sowing imported seed, bush burns, tussock fires, especially fire—these are among the important methods of direct interference. Not less than half the total surface of New Zeland has at least once during the century past been swept by fire—forest trees, the grassland plains, and scrub waste alike. The plough is not much used in New Zealand agriculture. Tillage and cropping is restricted almost entirely to the South Island plains and “ downland.” It was in the early days of extensive graingrowing and overcropping with bonanza cash crops, practised much more widely then than now that the plough irreparably damaged the natural value of the South Island’s better land. The soil problems of the South Island foothills and Canterbury Plains —erosion, exhaustion, and loss of structure —are a heritage mainly from the quarter of a century following 1865. Then, when sometimes 5,000,000 bushels of wheat were exported annually and the Canterbury Plains alone produced even more than that, fertility was mined and the light topsoil stripped by wind and water from most of the foothills, downlands, and plains of the lower rainfall areas. The principal indirect agents of soil changes—and ultimately of excess waste —are animals and plants. In the brief century of European occupation nearly 750,000,000 domestic animals have grazed the alien, deteriorated native, and inducedindigenous vegetation of New Zealand farm lands. In addition, millions of rabbits have nibbled the ground cover, and large numbers of deer, goats, thar, chamois and wild pigs have helped to deplete the taller vegetation of both occupied and unoccupied tracts ; and all this in a relatively small area which, before Cook, knew no grazing animals. “ Fern crushing ” with flocks of dry sheep was a regular practice in North Island pioneering. It is still practised in modified form, and heavy beef cattle are carried on

many hill sheep stations in the heavier rainfall districts of the North Island principally to trample fern, bidi-bidi and other self-growing second-growth plants in deforested areas.

Stocking has a double effect on the soil. It has helped the substitution of a new vegetation and, in many areas, has thinned out the protective plant cover. Equally important, though often overlooked, the pounding and trampling of stock has had the effect of compressing, consolidating, and puddling the topsoil, changing its structure and water relations and increasing dryness during drought and increasing run-off during rain. Moreover, the hill country is to-day seamed with millions of sheep-made contours, and each of these tracks is a silent witness to the extent to which stock trampling accentuates the downhill creeping, flowing, and slumping of soil. Evidence drawn from many parts of the Dominion is sufficient to illustrate the seriousness of the soil erosion problem in New Zealand. The ever accelerating rate at which topsoil is being washed and blown away, the increasing frequency of “ slips,” the almost daily damage to railroads and highways, and the recurrence of higher and still higher river floods—all these have suddenly brought a widespread realization of what a century’s possession has done to the land. They have also widened the sporadic agitation

for river-protective works and afforestation into a firm public demand for soil conservation. A new attitude to the land and fundamental social readjustments are demanded. In 1941 the Government was prevailed upon to sponsor and pass a comprehensive Soil Conservation and Rivers Control Act. Though operations —even research—have apparently been held up for the duration of the war, the Act will lay the foundations of what should be an important and essential aspect of post-war reconstruction in the Dominion. Despite the advance of agricultural techniques, in particular of pasture management, and despite the increased use of artificial fertilizers, the improved strains of stocks, crops, grasses, and clovers, and despite the reclamation and bringing-in of new land, New Zealand can show no comparable expansion of farm production. In recent years, in fact, carrying-capacity has remained barely stationary. It has been claimed that “ the countryside is intrinsically worth less for grazing than in 1870-80.” For this, soil erosion is largely to blame. We have examined the physical causes of soil erosion, but the real underlying causes are economic and social. This concerns us all very acutely, and it would be well worth your while thinking about and discussing what you think have been the social and economic causes of the decay of our soil.