The Vanishing Land

Cue (NZERS), Issue 15, 15 January 1945, Page 8

The Vanishing Land

— By

THIS article deals with some aspects of erosion, a subject which appears to .be simple, but is, in fact, very complex. It is a problem that can be tackled with a little understanding and common-sense, and yet it may well become a major problem in New Zealand.

Why pull the punches about it? There has been more ignorance and lack of common-sense, more downright selfishness about it than about any problem that New Zealand faces. Thousands of acres are denuded of their natural covering, degenerating into shingle slips, being wantonly destroyed, while the owners, like the Arab, murmur "Kismet.”

Thousands upon thousands of pounds are spent in New Zealand in building groins and stop-banks to control floods, but few think of tackling the problem at its root. Is it through ignorance? Yes! But, how many farmers are willing to study the question? The rule of thumb the "I-won’t-be-here-in--100-years" attitude, are all too common.

To show the seriousness of. the pro-, blem, here are a few facts and figures, taken from official statements: "The majority 1 of the agricultural land in the United States of America has been under intensive cultivation for just over 200 years, yet 55 per cent of the total land area is threatened by erosion... Out of a total land area of 1.903,176,620 acres... 282,218,000 acres had been so severely damaged by soil erosion that their future use for crops or grazing was economically unfeasible... that 775,678,000 acres had become so perilously eroded as to require immediate control measures to ensure continued productivity...” (Dr. H. Bennet,) In South Africa, "erosion is one of the main causes of rural poverty, both amongst Whites and Natives " (Dr. J.P. van Aartsen.) Tet it is possible to defeat erosion by taking certain rudimentary precautions. Take an imaginary cross-section of a hill. The core of the hill is solid rock. Thege is an outer layer of

broken-down or weathered rock, and outside that again is a thinner layer of soil, that is, very fine rock particles' with organic humus added. That is all one needs to know to fight erosion, because that is where the majority of the erosion takes place.

Erosion is not a matter of controlling huge rivers that carve away the . land like greedy animals. Rather it is the action of the rain’ the force of the drops and the impetus of the run-off that sweep most of the 52,320,000 cubic yards of soil down the Blue Nile, that •give the Mississippi yearly' 476,900,000 tons of the United States of America to carry away to the sea. What is happening is that this broken weathered layer on the outside of each hillside is settling like the salts will in a tin of fruit salts. When the slope is steep, and especially after heavy rains, it may slip fast as a landslide, because the waterlogged soil is heavier and water acts as a lubricant. But normally it. soon begins to settle slowly and as the bare rock at the top is exposed it is weathered and broken up. ,On such a hillside trees and grass

flourish, binding the soil with their foots. Remove the vegetation and the soil is exposed, cracking and drying. The falling raindrops loosen and carry away large quantities of the soil. The weathered parts slip and bare rock is exposed, giving the rain-wash more impetus. Soon* the exposed face is cu into valleys and ridges. For those who do not believe in t e effect of rain, here ? is a drawing

made from a photograph taken by Professor Cotton,, of Wellington!. It shows the results of rain falling in one direction only, making earth pillars and ” fingers.” The action is a double one, both washing away and dissolving.

The answer is obvious. Steep hillsides should be allowed to remain under vegetation. This will hold not only the soil but the moisture. Thus the lower and more valuable lands will be protected against erosion, flooding and drought. If the hillside is cleared, it should be done in blocks following the contours. If it is possible to plough the slope, it should be ploughed along the contours. Then the soil is held and erosion is small.

In New Zealand, erosion is a serious threat. The natural vegetation is of a type that is not adjusted to grazing animals and the native grasslands are rapidly disappearing. Remember that the deserts of North Africa were once called the granaries of the Roman Empire. That is forgotten now. The Arab, overgrazing with goats, was responsible. Overgrazing is more than bad farming; it is a crime. Another more wide-spread crime is burning off. It has seriously damaged the soil and speeded the erosion of the drier areas. If you hear the statement, ’’Well I won’t be here in 100 years,” remember

that erosion can destroy 50 per cent of New Zealand grasslands in a lifetime. Listen to the story of the ’’Dust Bowl” in America: in the early 1930’s a series of droughts destroyed the crops and grass, cracking and drying the soil. By 1934, a wind of under 30 miles an hour would raise such dust storms that in New York, 1500 miles away, cars had to use their headlamps. And thousands of farmers were ruined.

Floods too, are a result of the washing away of the soil; yet few people suggest tackling them at the root, i.e. on the watershed. No. They will spend thousands of pounds building stopbanks, even carrying the river above the level of the surrounding countryside. With the increased soil

erosion in the headwaters, the river cannot carry the load of material; so

it deposits it in its bed. When rain falls there is little soil to retain it, it runs off into the shallow bed, and there is a flood.

Simple; so why not tackle the problem by holding the water in the watershed? With wise afforestation the water and soil are held, the level of the river is more constant throughout the year, and valuable timber is produced so that there is a return for the money. The obvious answer is to create forests on the water-catchment areas, and to protect existing ones from fire and deer. Yet how little is done!

The type of erosion mentioned above, which can be called rain-wash erosion, is the most insidious and destructive type. River and stream erosion is noticed and generally controlled at once. This type of erosion takes place in three ways—by corroding the bed of the river, by solution, and by under-cutting

the bank. The last is the most important, but, provided the watershed is controlled, the actual erosion of rivers can be checked by planting willows,

poplars and other soil-binding plants. The main part of the erosive work of rivers is in carrying away the soil and debris that has been collected by washing higher up in the watershed. New Zealand is fortunate in that she is not over-populated. Unlike many European countries, she can afford

to keep catchment and more rugged parts of the country under permanent anti-erosion control. But she cannot afford to carry on what she is doing now, allowing her soil to melt away or be shovelled by the bulldozer-load into the sea. We can learn what has been done in the older lands. The answer is in our hands.

If this article provokes some discussion, if it presents a fresh point of view on this vital problem, above all if it produces some material results, it will have done something.

The answer is'in our hands provided we can be far-sighted enough and energetic enough to do something practical. There is still time to do it.