MENACE OF EROSION

Press, Volume LXXIII, Issue 22183, 28 August 1937, Page 16

MENACE OF EROSION

ALARM EXPRESSED BY MINISTER j i DAMAGE IN CANTERBURY WATERSHEDS OFFICIAL SUGGESTS REMOVAL OF STOCK A very serious view is taken Dy the Minister for Internal Affairs, the Hon. W. E. Parry, of the erosion menace in the watersheds of the great Canterbury rivers. In a special interview with "The Press" he issued one of the reports which he has had from his officers who 1 investigated conditions in these] areas. The disclosures are described i by the Minister as startling, and this particular report goes as far as suggesting that (if it is not already too late) the only way toj prevent further extensive damage is to remove all grazing animals, including sheep, from the high hills. "The information given in this report and the contentions expressed i about the damage already done by erosion and its potentialities for very widespread future destruction of good land make sad reading," the Minister said. The report, inter alia, states: "I have had opportunities to study conditions in many parts of New Zealand, and, in my opinion, the most pressing need for protective measures to-day is in Canterbury, and the area in mind is that portion of Canterbury which forms the watersheds of the Rakaia and Rangitata rivers. Before erosion set in in the high country these rivers wound their way through their upper valleys in most cases covering about one-third of the width of the valley with their beds, the other twothirds being grassy flats. Now, however, owing to the rapid erosion, the shingle is coming into these rivers so quickly that the water is unable to carry it away, with the result that .these upper valleys are filling up with shingle, and in many cases the beds of the rivers now cover the whole j width of the, valleysLimited Capacity "Many people say that it does not matter how much these upper valleys All up, but this, I think, is a great mistake. These valleys can only hold a certain amount of shingle, and then where is it to go? Out through the gorge and into the river bed below. This must result In the filling up of the river beds across the plains, and, as the river beds rise, the water will flow out over the surrounding country. No doubt flood banks will be built —and will for some time do good work, but if the shingle is going to keep coming down it is only a matter of time until it will rise to the top of the highest flood bank. I understand that the- level of the river bottom at the Rakaia railway bridge has risen several feet since the erection of the bridge. The only way, in my opinion, to prevent this, is to strike -at the root of the trouble and try to prevent erosion' in the high' c6untry. "Before the advent of grazing animals the vegetation on the hills was such that it regulated the quantity of debris coming into the rivers and also greatly retarded the inflow of water so that instead of pouring into the rivers within a few hours after rain, as it does to-day, it took days to seep through, and that greatly helped to prevent floods. However, with the advent of the grazing animals this natural balance has been upset to an amazing extent with the result that when we get a heavy rain now we also get a flood as the water just pours off the hills, carrying millions of tons of debris with it. I think the only way to regain this natural balance is to remove the agencies which have upset it, i.e.. all grazing animals and prevent burning. "Deer Not Only Menace" "It is well known that deer do a tremendous amount of damage in this type of country by killing the bush and scrub and eating off the tussock, etc., but, in my opinion, there are other agencies which do as much or more harm than the deer. For instance, the number of deer the country can carry is regulated by the amount of feed available in the winter and, as this is always limited, it only allows a certain number to survive, so that there Is always plenty of summer feed and no danger of the summer country getting eaten out. This, however, does not apply to sheep, as many runholders nowadays send a large portion of their flock down country to winter. Where this is done, of course, the summer country must suffer, for we find that it has to carry, in addition to its deer. a good many thousand sheep. All grazing animals prefer young plants to old, and so kill the young first and then, if feed is 'short' will eat down and-often kill the oldest tussock. No doubt each animal will kill thousands of plants in a year. "When in its natural state most of the lower slopes of the area forming the head watershed of the Rakaia and Rangitata rivers was covered with bush and scrub, while the higher slopes had the usual alpine plant life, such as tussock, grasses, and scrub. It must be remembered that sheep do not thrive on scrubby or bush country, but the early settlers realised that if they could get access to the high country they could summer sheep there. So they set out to burn at first. I believe, just to get access, but it was found that after these burns tussock and native grasses took the place of the bush, thus forming good grazing country, so they then set out to burn as much of the bush as possible. Effect of Burning "Thi3 resulted in huge areas of bush being burned, and the only places to escape were dark, wet gulleys, where the bush was too damp to burn. Owing to the short time required for the tussock and grasses to come after a bush fire, it was only a matter of a few years until there was enough dry tussock and grasses to carry another nre, and it was this second fire that prevented the country from going back into bush, as all bush seedlings which had struck were then killed. No doubt for a good many years this appeared to be a very satisfactory state of affairs, and, in fact it is only in quite recent years that the great damage then done has become apparent, because it took a good many years for the roots of the trees to rot. as they, although dead, continued their job of holding the country together. Now that they have rotted it has become only too apparent that the tussock and grass wnich have replaced them are unable to do their work. Slips and shingle slides are starting and huge cuts, often 20 feet deep, reaching from the top to the bottom of hills, are often to be seen. "Most runholders believe that to get the best grazing off tussock country it is necessary to burn it as often as it will carry a fire. This in a climate that gets a heavy rainfall is usually •boot three to flva-jpers. Runholders,

will say that if burned at the right time of the year, i.e., in early spring, the fire will not do any harm and this, to a certain extent, is right, but the point is they do not always burn at this time. In fact, much of the burning is left until the shearing muster, which takes place im November or December, and this is much too late to burn country which lies to the sun, as it is too dry and the sun too severe. In most cases where large areas are burned, the fire will run over some portions where the ground is very dry and the shingle is very- near the surface or up to the edge of shingle slides and slips. On such areas as this, the tussock was having a struggle, against great odds, to hold its own before being burned, but after the fire the odds usually prove too great and, the tussock dies. i Mustering' Fires "In areas where the ground is very dry, or the shingle very near the surface, new shingle slides will result, and in cases where the fire burns up to the edge of existing slides the tustock will die for some yards back from the edge of the shingle, with the result the slide has become so many yards wider. This is going on year after year, and will continue to do so as long as sheep are permitted to run on the high country. Besides the intended burning, fires often get away during mustering, sometimes in the summer, and often in the fall, and these do unlimited damage, as they usually kill all plant life on the area burned. Another factor, which often causes much damage to the plant life, is for a shepherd, after having difficulty in getting sheep through a patch of scrub, to put a match in it, irrespective of place, time of year, etc. I think the only way to stop this terrible erosion, if it is not already too late, is to absolutely rid this area of all

grazing animals, such as deer, sheep, I thar, and chamois." ' "" '