The Gisborne Herald. WITH WHICH IS INCORPORATED “THE TIMES." GISBORNE, MONDAY, JULY 10, 1939. CONSERVING THE SOIL

Gisborne Herald, Volume LXVI, Issue 19985, 10 July 1939, Page 4

The Gisborne Herald. WITH WHICH IS INCORPORATED “THE TIMES." GISBORNE, MONDAY, JULY 10, 1939. CONSERVING THE SOIL

An important contribution towards the investigation of tlie problem of soil erosion is made in the report of the committee of inquiry set up last year by the Department of Scientific and Industrial Research. Since the committee held only two meetings and made no field observations, if will be realised that its report does not pretend to be the last word on the subject. Its members, all experts in one scientific branch or another, however, were enabled to pool their individual knowledge and were aided by reports from the officers of various State departments. With this background they have been enabled to compile a survey which will provide a basis for future measures designed \ combat a deleterious trend in the development of the country. It required no expert investigation to disclose that soil erosion was one of the most serious problems confronting the Dominion, but the problem did require a scientific approach if adequate steps were to be taken to ensure that land deterioration in its various forms was

not to be a continuous process with consequent inevitable increases in the

loss of production. The report that has now been issued can only be regarded as the first step in the right direction and it is most important that the matter should not be allowed to rest there.

The committee points out the necessity for differentiating between normal erosion, which is an essential process that will continue, and the acceleration of the normal process induced by man’s interference. With the former there is no occasion to deal, since there is a natural adjustment, but man-induced erosion must be counteracted because there is no compensation for it; in the absence of remedial measures it must lead to the gradual destruction of the soil. The committee refers to five types of erosion—wind, sheet, and gully erosion.

soil creep and mass movements. These, it is pointed out, are al! contributed to and accelerated by the baring of the hillsides, and althougl some can be effectively controlled b; the substitution of grass for bush cover, there are other factors which are beyond economic control. When there is not adequate control, there is not only the problem of erosion, but also the allied one of rivers abnormally charged with silt which, in time of flood, is deposited on fertile plains. The real problem, then, is to determine at what point the denudation of hillsides becomes a danger and what

steps are necessary to remedy the damage that has been caused by past mistakes. The committee lias started off by investigating the primitive vegetable cover of New Zealand and analysing the changes that have been made through settlement. It is estimated that originally there was 41,000,000 acres out of a total of 00,000,000 covered by forest and shrubland, and 17,000,000* acres was represented by tus-sock-grassland. Now, however, the forest acreage has been reduced to 23,000,000 acres and tile tussock lands to 14,000,000. The chief cause of this change is the fact that 18,000,000 acres have been converted to sown grassland, while another 1,500,000 acres, is in cultivation and nearly 1,000,000 acres is accounted for by boroughs, roads, and railways. These figures summarise the change that has been brought to New Zealand by civilisation. Somewhere, also, they explain the cause of the problem of e:osio». The first important conclusion arrived at by the committee is that the area of forest and shrubland is not below the minimum requirement; the real difficulty is that the forests are improperly distributed. It seems, therefore, that whatever steps are taken to prevent erosion, it will not be necessary actually to reduce the area of land in cultivation, but that as new areas are brought in others will have to be reafforested to prevent further

degradation; in other words, careful planning must replace the haphazard methods of the past. The need for a scientific approach

to the problem is made abundantly clear by the report. In the first place, rainfall plays an important part in determining what land can successfully be cleared of bush and replaced with pasture. The altitude of the area is also a factor and the steepness ol the hillsides another. The report points out, for instance, that the general experience is that good turf protects slopes very well, though not so well as the forest, it deplaced, but it is added that there is a critical slope above which it is dangerous to clear forest. This varies, not only according to the climate, but also according to the nature of the underlying rocks. This point emphasises the scientific nature of the whole question. Decision as to whether land can be successfully cleared and grassed does not depend solely on the judgment of even the most successful farmer, but must, to some extent, be based on the investigations of the meteorologist, the botanist, and the geologist. Nothing more need be said to emphasise the comprehensive nature of the study that is required if erosion is to be checked, and, more than that, if land that already is affected is to be restored to a stable condition. The report of experts provides a basis for future activities, and the responsibility now rests on the Government to see that further appropriate action is taken.