Desertification is the degradation of land in arid and dry areas,resulting from human activities and influenced by climatic variations.The primary reasons for desertification are overgrazing,over cultivation,increased fire frequency,overdrafting of groundwater,increased soil salinity,and global climate change.A major impact of desertification is loss of productive capacity.In Africa,for instance,if current trends of soil degradation continue,the continent might be able to feed just 25% of its population by 2025.Desertification is also widespread in many areas of China.The populations of rural areas have rapidly increased.While there has been an increase in livestock,the land available for grazing has decreased.Also the importing of European cattle,which have higher food intakes,has made things worse.A number of solutions have been tried in order to reduce the rate of desertification and regain lost land.Oases and farmlands in windy regions can be protected by planting tree fences or grass belts.Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts.Small plots of trees may also be scattered inside oases to stabilize the area.On a much larger scale,a "Green Wall of China",which will eventually stretch more than 5,700 kilometers in length,nearly as long as the Great Wall of China,is being planted in north-eastern China to protect "sandy lands" – deserts created by human activity.
英文,沙漠化,急用!我要一些英文的回答．急用!关于沙漠化的一些问题．比如说危害,原因,是否是全球问题,怎样防治．要一些简