Dunes: the fight goes on
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CTA. 1989. Dunes: the fight goes on. Spore 24. CTA, Wageningen, The Netherlands.
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The advance of the dunes is now a major worry for all those concerned with agriculture and the environment in Sahelian countries. The dunes pose a real threat to the infrastructure serving these countries. To combat their advance, governments and...
The advance of the dunes is now a major worry for all those concerned with agriculture and the environment in Sahelian countries. The dunes pose a real threat to the infrastructure serving these countries. To combat their advance, governments and populations alike have initiated a series of measures - mechanical, chemical and biological. There is nothing new in this battle: since ancient times man has struggled against the dunes which, day by day, creep inexorably onwards, swallowing fields, oases, roads and tracks, and village gardens. But nowadays the situation is aggravated because the dunes are no longer stabilized by vegetation, which has been destroyed by drought and over-use of the land. No country in Sahelian Africa is exempt; the Senegal River is under threat, as are the Route de i'Espoir in Mauritania, all the Saharan oases, the niayes in Senegal and the pools in Niger. Manual control methods There are several methods in current use which can stop the dunes in their tracks. Perhaps the crudest is to remove the sand mechanically or manually with a digger, or even with bucket, spade or pan. Sometimes traditional methods are still used - such as shovelling the two ends of 'barkhane' a crescent-shaped dune: the dune collapses once its balance is thus destroyed. In some places artificial dunes are built to retain the sand and so leave clear the fields or gardens behind them. Other methods include applying petroleum products, which stick the grains of sand together, as the ancient Egyptians did with natural tar. The chemical industry is trying to improve this practice, which is both polluting and foul-smelling, and will soon be ready to introduce compounds which, when mixed with water and sprayed on the sand in a fine mist, will create a network of small fibres which immoblizes the sand. This solution seems promising, but is still far too expensive to be used on a large scale. Building breaks or planting trees Another traditional method of stopping the advance of the dunes is to put obstacles in their path. The most usual way of doing this is to weave hurdles of branches and sticks to hold back the sand, using locally available materials - millet stalks, esparto twigs, palm leaves. Modern industry is trying to take up and improve these peasant methods, especially where vegetation is scarce. But once again the man-made fibres and plastic materials which have come onto the market are too costly. Tree-planting remains the most popular method at present. Prosopis, filao, balanites and acacias are closely planted in rows across the area to be protected. 'Planting trees on dunes in areas with an annual rainfall of 200 to 100mm is not an impossibility: the bare surface of the dune is porous and soaks up rainwater like a sponge. The water is then filtered downwards rather than running off', explains Rene Marceau Rochette, who is a consultant with CILSS (Comite Interetats de Lutte contre la Secheresse au Sahel/lnter-state Committee for the Control of Drought in the Sahel). Over the entire Sahelian region small farmers are starting to plant trees to fix the dunes, and these have the added advantage of providing extra wood, fruit, forage, and medicinal products. But here once again the long-term eflectiveness of this method is being called into question by the experts. The growth rate of the oldest plantations has virtually come to a halt in the past two years - perhaps because the sand's reserves of nutrients have been exhausted by the abundant vegetation, or perhaps the plantations and years of drought have dried out the dunes. Agronomists are being cautious until they know the answer to these questions. Stopping the creation of sand Since none of these methods is a permanent solution, research scientists at CTFT (Centre Technique Forestier Tropical/Tropical Forest Technical Centre) see that any potential remedy must strike at the root of the problem:'The people are wearing themselves out trying to arrest the progress of the sand, but it never stops coming. Its source is limitless, and unless we can attack that, everything else will just be a stopgap solution', says Michel Malagnoux of CTFT. 'We must try to prove that a country's infrastructure can be effectively and enduringly protected once the agricultural and pasture lands where the sand originates are properly and sensibly managed'. This means protecting existing vegetation over the whole region, planting trees, controlling the movement of herds and flocks and making sure they do not destroy everything in sight, and legislating in order to stop bushfires. If these measures are taken then the dunes will neither form nor advance. For more details, contact: Michel Malagnoux - Centre Technique Forestier Tropical 45 bis avenue de la Belle Gabrielle 94130 Nogent-sur-Marne - FRANCE
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