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Counting sheep against dust storms

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​​​Every spring, dust storms sweep over the wide grass steppes of ‘Inner Mongolia’ in northern China with their intensity increasing from year to year. They carry enormous amounts of dust over thousands of kilometres to Beijing and beyond. For six years, a German-Chinese joint project investigated the causes. Researcher Dr. Carsten Hoffmann compiled the results for the first time in order to offer concrete solutions.​

For hundreds of years, the nomads of ‘Inner Mongolia’ and their herds of cattle roamed the grassland. During the hot summers, the herds grazed on the cool plateaus, in the icy winters they moved into the sheltered valleys. Low rainfall and extreme temperature differences on the steppe did not allow for anything other than this very limited form of livestock breeding. When ‘Inner Mongolia’ became a Chinese province 70 years ago, new forms of animal husbandry were established. The land was divided up, settlements were built. Sheep and cattle have been kept on fenced-in pastures ever since. The ‘Inner Mongolian’ grass steppes, with an area of more than 1 million square kilometres, are now the largest of China‘s five stockfarming areas. But intensification exacts its toll: The pastures are undergoing increasing degradation. In the past, these grasses – some of them as tall as a man’s head – slowed down the dust storms from the adjacent Gobi desert which now sweep freely across the land. Even worse, desertification makes the steppe itself a source of dust emissions – with tremendous consequences. In March 2002, a gigantic storm deposited more than 30,000 tonnes of sand and dust over Beijing, i.e. around two kilograms per inhabitant.​

 

International cooperation to solve a global problem​

Similar challenges can be found today in many places around the world. Worldwide, 1877 megatonnes of dust are stirred up by wind erosion every year and this is often due to overexploitation of sensitive dry areas, such as the steppe. The dust storms of ‘Inner Mongolia’ quickly attracted the attention of the international scientific community. In order to study the influence of intensive livestock breeding, ‘MAGIM’ was launched in 2014 as a German-Chinese joint project funded by the German Research Foundation. For six years, some 40 researchers from both countries studied various aspects of sheep pasture farming in ten sub-projects. The aspects studied included, for instance, the impact on soil physics, plant growth, species diversity, local climate and hydrologic balance. Dr. Carsten Hoffmann from the Leibniz Centre for Agricultural Landscape Research (ZALF) also repeatedly visited the research area measuring more than 500 square kilometres, bringing with him equipment for measuring wind erosion. »In the spring of 2006, I investigated a 147-hectare fallow field surrounded by well-preserved grassland,« reports Hoffmann. »I noticed a high wall of sand on the eastern boundary of the field.​ ​​When the spring storms began, the wall grew visibly larger, as the coarser soil particles that were swirled up got caught on it whilst fine particles flew over the wall and were removed from the field.« His measuring instruments indicated that the resultant loss of soil totals around 136 tonnes per hectare. »To illustrate this, imagine a football field, from which ten truckloads of fertile fine soil is removed during just one spring,« explains Hoffmann. »On the adjacent grassy pasture, we measured average dust emissions of just up to 2.5 tonnes per hectare.« However, the values increased with increasing grazing intensity. Highly stressed areas already showed loss rates of a critical 5 tonnes per hectare, which makes them ‘hot spots’ for dust emissions in addition to arable land.

 

From data collector und data manafe

The ‘MAGIM’ project became be a success. The individual results appeared in more than 130 publications and have been cited almost 3,000 times so far. At ZALF, Dr. Hoffmann prepared the first-ever compilation of the results of all sub-projects in a research article: »I found it exciting to compare the findings of others with mine and to develop viable strategies for the local population: When can sheep be allowed to graze, how many sheep per unit of area are still sustainable? Even though each of us looked at a different aspect, we all came to similar conclusions: »Intensive grazing compacts the soil. Storage rates of water available for the plants decrease by around one third. This makes the roots shorter and weaker – vegetation renewal is impaired. Biodiversity declines rapidly. Wind erosion causes a loss of more and more fertile soil, so that the regeneration of the plant cover is impeded even further. Another observation concerns the carbon footprint: Carbon that was previously bound in the grasses by photosynthesis is released in the form of methane and carbon dioxide as a result of intensive animal husbandry in such quantities that affected steppe areas become greenhouse gas emitters. But there is no need to do without animal husbandry entirely, says Hoffmann: »The intensity of grazing should be adapted to the amounts of precipitation, since this has a crucial influence on animal feed supply and the ecological resilience of the grassland. In humid years, the animals can graze on the pasture as usual.​​ However, the favourable conditions should also be used to produce more hay. A certain amount of nitrogen fertilisation is recommended here since the nutrient supply from animal dung is not available on the respective areas. In dry years, grazing should be reduced to less than two sheep per hectare and the animals should be given additional hay in the stable instead. Individual pastures could be additionally protected by regularly rotating flocks between defined areas.« 

According to Hoffmann, this strategy can help to prevent further degradation of the grassland. All that remains now is to convince local stakeholders of a new folk saying: Counting sheep against dust storms.

 

Text by Jana Schütze

 

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