EROSION MENACE

Dominion, Volume 37, Issue 11, 8 October 1943, Page 6

EROSION MENACE

Immediate Tackling Or

Further Disaster?

ALTERNATIVES PUT BY SCIENTIST

Further disaster and much suffering would come to many parts of New Zealand unless, most scientists with a knowledge of the problem agreed, au attempt was made in the immediate future to grapple with the erosion problem in a scientific and practical way, writes Air. J. T. Salmon, Al. Sc., A.R.P.S., in an article on “Erosion Control and Rehabilitation,” published in the “New Zealand Science Review.’’ Few would deny, lie says that the phenomenon of accelerated erosion had become a serious and menacing problem.

The occurrences of recent years at Kopuawhara, Esk Valley, French Pass, Southland, and other places, popularly but incorrectly attributed to cloud bursts, merely were a foretaste of what would be occurring throughout the length and breadth of tins country with increasing frequency and increasing severity unless past errors of land utilization were corrected and possible future errors minimized. Flood control works, such as the building of stopbanks, groynes, the dredging of river channels, and other river bank works were only palliatives that-treated with the effects and results of high country erosion. They neither tackled nor recognized the real causes of the frequent flooding and accelerated erosion occurring in New Zealand. Travelling about in tine hill country of New Zealand, especially in certain areas of the North Island, one was confronted on every side with the phenomenon of accelerated erosion in its incipient and advanced stages. About one-third of the land area of the country was now subject to the action ot this destructive force: and the area continually was increasing. Accelerated, erosion not only led -to a scarring, slipping and eventually useless, steep hill country, where it commenced, but also to aggradation and expansion of river beds, to rapid water run-off. and to floods which carried and deposited material ill the form of boulders, stones and sand over fertile low country lands, rendering them also useless or nearly so. Great alluvial fans, fed by accelerated erosion, were spreading out over acres and acres of useful land in many areas of the South Island, while aggrading rivers and.great floods were becoming commonplace all over the country. Effect of Deforestation. Some idea of the extent of deforestation in New Zealand and its bearing on accelerated erosion could be gleaned from the fact that during the past 94 years 15,000.000 acres of forest land had been cleared of forest, the greater part, particularly in the hill country, by burning. During, the same period afforestation from all sources had amounted to only 852,1.16 acres, practically all of which had been planted in exotic trees. Very little attempt had been made to utilize native timber-producing trees for, reafforestation, only a few hundred acres having been planted for experimental purposes. The present white pine shortage would not exist if an energetic policy of reafforesta-' tion of kahikatea, forests had been commenced 50 years ago. Reafforestation which had been carried out had been for timber production purposes only, and planting had been on poor, almost waste, lands not subject to accelerated erosion. From even a cursory examination it was evident that much of the hill country which had been cleared for farming should never have been deforested. It was evident also that reafforestation of all affected country would not solve the problem. On steep hillsides reafforestation was' the one and only solution, but on gentler slopes the. maintenance of better pasture cover and the practice of erosion control methods which had been proven in other countries, notably the United States of America, would help bring accelerated erosion under control.

It was’ significant that little if any attempt had been made in New Zealand to put .into practice approved methods of erosion control or to devise new methods more suitable to the particular conditions appertaining here. Over-grazing, burning-off, the slaughter, plunder and exploitation of high country forest continued. During the past 50 to 60 years the voices of prominent New Zealand scientists had been raised in protest and Warning against the disastrous consequences of land utilization policies, but they had been as voices crying in the wilderness, till today the very things of which they warned were occurring on every side. 1 Planting on Steep Hill Country.

' To be brought under control accelerated erosion must, be tackled first at its source, i.e., in the steep hill country where the only method of control was reafforestation.. This would mean reafforestation on a very, large scale, larger than ever before attempted in New Zealand, possibly on the scale of 100,009 acres a year, for a period of years. Such a scheme of afforestation could be made the basis not only of a large rehabilitation scheme at the close of the war but also of extensive new timberproducing and wood by-products Indus-: tries. Reafforestation of the hill country on sound scientific lines and on a perpetual replacement basis could establish New Zealand in the future as oue of the major wood-producing countries of the Southern Pacific. Wood was the one great replaceable raw material available to man; and wood and wood products., specially wood pulp, would be in ever-increasing demand in future years. Reafforestation and land utilization on a proper scientific basis could not be undertaken without the preliminary of an extensive land survey. The purpose of such a survey would be, first, to decide what land should revert to forest, having regard to the degree of slope, the nature of the soil and the climate of each particular area under review.

Such a survey could be undertaken by (he combined activities of the Soil Survey, Forestry Department and Plant Research Bureau; but Mr. Salmond suggests the time has arrived for the setting-up in New Zealand of an adequately supported and equipped land utilization’ and" biology research bureau to don! with the-problems of erosion, land utilization, and related problems, as well as with wild life research and control, together with their related problems.