WANDERING SAND.

Shannon News, 1 June 1923, Page 4

WANDERING SAND.

LESSONS FROM FRANCE. OVER A CENTURY’S EXPERIENCE In .title course of his enquiries regarding the fixation of vagrant sand dunes, the “Chronicle’s" representative was greatly assisted hy the 'Officers of the Forestry Department. Hi a attention was drawn to the successful experiments carried on fcy French authorities for well over a century, and he became aware that here was evidence that “they do these things better in France." The .second article of the series gives an outline of the methods of fixation employed there and the effects.

In his treatise on “The Fixation of the Duneg of Gascony,” a translation of which is issued by the State Forestry Department, M. Edouard Harle, describes the process found most efficacious in that part of France where this sand hill s were, according to the description of Le Boullenger, quoted by (him, of exactly the same nature as ours, long waves of sand drifting inward from the sea by a long slope on the aide of the prevailing wind, and then breaking away in chunks down a steep further slope. He speaks of the sand advancing with great rapidity and) being a menace to the community from, two sources—one that it threatened to overthrow villages, and secondly through the Mocking of streams, forming lakes in the interior. similar damming up may be found on the New Zealand coast, the Buller Lake being undoubtedly an example of an old creek bed being raised by sand and forming a lake in an interior depression. In France the whole problem was dealt with by a bold policy of afforestation, practically the whole ; of the dunes in Gascony, covering an area of 240 kilometres in length and from 4 to 8 kilometres in width being put under forest. Such a course in New Zealand would be impracticable owing to the cost, which when it is understood that the State Forest Department estimates that the preliminary work will cost something like £25 per acre, will be seend to be considerable, there is no doubt however that a protecting belt of trees must be planted along the foreshore, and we can consult Le Boullenger again .as to how these can be successfully established in the drifting sand. “The most rational thing it would appear," he writes, “was to begin fixations on the Coast, ’and continue them towards the interior. The progression of sand was thus arrested at the start, and each work was protected by the preceding one against encroachment. But with this plan, the dunes continued to encroach upon the land right up to the completion of the last work. It was therefore preferable to commence on the landward side of the dunes and place successive works from the interior towards the sea.” In the very first work, commenced in 1787, by Bramontier it is stated that

small fences of brushwood (clayonnages) were erected in the sand, 10 metres (about 12yds) behind one another. in between, seeds of pine and broom wiere sown, which germinated; but when a rather strong wind came, it moved the sand, uprooted the young plants, .and .overwhelmed a number of the brushwood fences, or overturned them. The impossibility of fixing the sand without a covering was then seen.

The first step then was to arrest the drifting sand from the ocean in order to prevent new supplies arriving to cover any work undertaken, and this was accomplished by the erection of palisades of boards about five feet in height and one foot in breadth, driven into the sand with inch intervals between boards, the space being left so that sand might filter through and buttress the palisade at the back in proportion as it was loaded on the windward side.. When the sand had risen and buried the fence to a certain level, the boards were lifted and planted higher, the result being, in time, the formation of a sand ridge or 'littoral dune.’ This dune was naturally subject to breaks in heavy storms, but by the erection of , works could be made to repair itself .by the action of the wind.

The arrival of new sand being prevented, the reclamation proper could be proceeded with. The boundaries of the area to be reclaimed would be decided on, and protected to the side, if necessary, by the 'clayonnages’ mentioned earlier. As the works were started at the limit of encroachmient, it will be remembered, it was also necessary to erect protecting fences in front at each stage of ihe fixation.

The French scheme was one of sowing, and not of planting the dunes, the reason for which will he apparent later, the mixture recommended being 451b s of pine-seed, 201bs broom, and lllbs of marram-grass seed per hectare (2 1-5 acres). *me uSe d was

the ordinary maritime pine, and the addition of the broom seed was f~r the purpose merely a§ Bremontier was careful to point out, .of affording protection to the young pines. The important part of the .work now commences, .and that is the ‘couverture’ or covering of the area sown, with branches, to prevent the disturbance of the surface, by the wind. At this point it may he pointed out that on the landward side of a dune, that is the steep side it was .at times found necessary to break down the steepness of the slope, which was done by employing peasants to tramp up and down, causing the sand to run down to the bottom until a satisfactory slope .was attained.

In connection with the covering of seed, Jemois wrote on May 30, 1820: “Seed shall be covered by boughs trimmed fanwise Ilk© the branohlets of trees on opposite branches. To this end all twigs above or below, which would prevent the branch lying flat on the soil are to be cut off. These branches will he laid as exactly as possible on the surface of the stil, superimposed one on another, like the feathers on a bird’s body. This covering to be kept on the ground \<y shovelfuls of sand thrown on at intervals. On steep slopes, as the branches cannot be weighted down, .'he butt to be thrust into the sand.” (Manuka should make an admiraole substitute in New Zealand for be pine-branches found most suitable in Frer.ce). Thi & covering not only prevents the shifting of the sand, but provides shelter for the sprouting seed

In 1833 Deschamps Junior pointed out that the sowing should be dour, as near as possible, in zones parallel to the prevailing winds, taking pat ticular care to set the lines of r.mverture in the same direction, the butt end of the branches being placed toward the wind, or in some cases laid parallel with it. This covering is a serious affair and in France special fixations were made at times in certain central places for the purpose of providing brushwood for the completion of tiie works some years later. Even then the cost of transport of brushwood amounted in some cases, to twothirds of the entire cost of fixation. It was recommended that branches over-lap one third of their length, but in less exposed places such as flats between dunes, a half-covering or ■demi-couverture’ was found sufficient, although there being practically no shifting sand on the flats the sowing was rather for the purpose of afforestation than fixation, and in fact, in most instances, fiats were dealt with by transplanting rather than sowing. Most of the work in France was dome by contract, the terms of the contract stipulating: “The contractor is responsible for success until three years after the last sowings have germinated. The annual germination is declared favourable to the contractor when the seeds have sprouted—during the first year, fifteen stalks of pine, and the same of broom per square metre; the second year, ten stalks of each species; and the third year six stalks of each species." The littoral dune was “fixed" by plantings of marram-grass.

The importance of keeping stock off the dunes if fixing is to be successfully accomplished—whatever the method used—cannot he over-empha-sised. Le Boullenger, in his report of 1817, even asserts, “It is probable that if the dunes were left to themselves, and not covered with numerous cattle which shave off and tear out all plant-life which grows there, the vegetation would soon get the upper hand, and overcome by degrees all moving siands.” That this would appear to be merely a statement of fact, although spoken of in Harle’s report as an “exaggeration” is instanced by the local sand-hill system where, a s has been mentioned, the sand-hills-relios of a former drift—were covered up to 40 years ago, right out to the coast. However this process would, naturally, be a slow one, and economically wasteful, besides allowing for the submergence of a possibly considerable further area before it takes place.

So much for the French system. As will he seen, no attempt was made to reclaim the land with a* view to future grazing. Forests were desirable, and the sand had to be stopped, and us the cost was, comparatively, small, amounting over large areas to about £2 per acre, forests were accordingly made. in New Zealand, however, where, according to the report of the State Forest Department the cost of fixing the sand on a drift may possibly be as much as £25 per acre, conditions are considerably altered.