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Degraded Land in South China Damaging agricultural and

游客2024-02-27  13
问题                      Degraded Land in South China
    Damaging agricultural and forestry practices over the past years have degraded half of the land in China bounded by the Tropic of Cancer and the South China Sea, dramatically reducing its biological productivity and environmental services. The damage to South China’s hilly tropical/subtropical(亚热带的) forests probably began in the Sung Dynasty as population expanded to the south. The settlers most likely used cutting and bum techniques to clear land for fanning. Forest cover provided building materials and firewood to the settlers, but also served as a habitat(栖息地) for tigers, leopards, wild pigs, and deer. Population growth put severe pressure on the land. Eventually, erosion (腐蚀) washed away much of the top soil and much of the degraded land was abandoned. Today, only about one square kilometer of the original tropical evergreen broad-leaved forest remains.
Impacts
    The most direct impact of this disastrous loss of productive soil is reduced agricultural production. Farmers trying to produce crops under these conditions face great difficulties even when using commercial fertilizers(化肥). The soil is poor at holding the plant nutrients(营养) contained in commercial fertilizers. The problem is deteriorated by the fact that fertilizer runs off the land quickly during heavy rains.
    China cannot afford to abandon potentially productive land, let alone lose more to erosion. It is already losing enormous amounts of land to new towns and other non-agricultural uses. Per capita amble land (人均可耕种土地) in China now is about 0.1 hectare, only 47 percent of the world average.    But China estimates that it lost about 50,000 square kilometers of its amble land from 1986 to 1995, the equivalent of the total agricultural land area of Japan. Food production is not the only problem. The loss of much of China’ s forest cover today has made wood products China’ s leading import costing the country $ 2 to $ 5 billion annually.
    Economic losses also result from waterlogged (水涝的) fields and coastal sand storms that result directly from the soil erosion. Some 710 million tons of sediment(沉淀物)were carried through the Three Gorges(三峡) part of the Yangtze in 1998--a 33 percent increase over the loads measured before    1990. In parts of Guangdong Province, sediment-choked streams and rivers have caused the water table to rise and have waterlogged nearby farm fields. Since the waterlogged land is useless for conventional fanning, the Chinese introduced the "dam-pond system". Ponds are dug and used for raising fish and vegetables are grown on the tops of the dam surrounding the ponds.
    This system may have to be ridiculously stopped if erosion is controlled. Once controlled, the streams and rivers will cut deeper channels, thus lowering the water level in the fishponds. In the few areas where reforestation (重新造林) of eroded hills has reduced erosion and sediments in the rivers, the river has begun to cut through years of deposited sediment to return to its original bed. This lower water table(地下水位) reduces water logging of nearby land and the fishponds begin to dry up. In some places, pumps had to be installed to draw water from the streams and rivers to keep the water level in the fishponds stable.
    Sandstorms are another effect of the heavy sediment load created when granite (花岗岩)weathers (风化)in the wet tropics. Coarse quartz(粗的石英) sands move from the weathered hills to lower elevations    during heavy rains, filling valleys and covering agricultural fields. Fine-grained quartz sands, however, are carried further downstream and deposited near river mouths. Strong sea winds and typhoons regularly blow the sand inland, burying agricultural fields and human settlements. To reduce the movement of sand by wind action, the Chinese built windbreaks(防风林)along much of the sandcovered coastal belt. Salt-tolerant (耐盐的)trees, satisfactory for such coastal windbreaks, were planted near the shore. Because these trees are exposed to local people looking for firewood, the government normally prohibits tree cutting but allows them to dump rubbish beneath the trees for cookingfuel.
    Loss of covering plants and soil means that heavy tropical rains flow rapidly into streams and rivers, causing disastrous flooding. The damaging floods and landslides(山崩) in lands adjacent to the Yangtze and Yellow Rivers in 1998 were a direct consequence of the loss of forests and other plant in the rivers’ headwaters(上游) and over-fanning. These floods killed many and destroyed homes, roads, bridges, and other construction. In Jiangxi province alone, the government had to resettle 600 thousand people from along the flooded Yangtze River.
Some Solutions
    Scientists in research institutions throughout South China have worked for decades to develop and test methods for restoring degraded lands to productive lands using a combination of agriculture and forestry methods called agroforestry. Since funds are scarce and the problem is large, any practical solution must be able to begin creating an income for .the region’s farmers within a few years. This has led to some creative and promising strategies for restoring some of the most severely weathered regions. Techniques, of course, must be adapted to fit each cultural and environmental region. Many of the most effective approaches rely on knowledge gathered from traditional systems practiced by ethnic minority groups in the affected regions.
    The process starts with a fast growing ground cover that can shade the soil and make it possible for other seeds to grow. Care must be taken to ensure that this new cover survives the dry season when grass fires present serious hazards. Fire prevention can be extremely difficult in areas where open flames are used for cooking and for religious practices. These early plantings are typically made at the beginning of the rainy season when the ground is comparatively cool. ]’he wet season gives the plants an opportunity to establish themselves and provide leaf cover for shade. It is essential to pick pioneer species that can provide some income for farmers in the first year income that will sustain the farmers until other crops establish themselves.
    Part of the art is finding a combination of crops that can occupy the same site. Above ground, this means matching demands for sunlight and shade. Rubber trees, for example, require bright sunlight,    but valuable herbs(药草) can be grown in their shade. Below ground, it is essential to arrange mot systems of intercropped plants so they do not compete excessively for water and soil nutrients.
    Once established, these systems contribute organic material to the soil, slow rainfall runoff, help make up groundwater reservoirs, and reduce water and wind erosion. Deep tree roots help to fix the soil and prevent landslides, and the shade from the leaves lowers the local surface air temperatures, facilitating crop growth. In many eases, birds and other wildlife return to reestablished habitats (栖息地) in the area.
    One of the greatest challenges is finding ways to make productive use of the varied type of land of Southern China—including the steep hillsides. Fanning hilly areas is essential because urban development is forcing farmers off many lowland areas. A technique called stereoagriculture has been developed    in which forests are restored to the hilltops while a mixture of intercropped orchards (果树)and food crops, fishponds, and small animal grazing(放牧)are introduced in the flatter lands below. [br] Windbreaks are planted along the sand-covered coastal belt to reduce the movement of sand blowing inland by wind action.
选项 A、Y
B、N
C、NG
答案 A
解析 第一小标题下第五段介绍了沙尘暴是湿带地区花岗岩风化造成大量沉淀物的结果。风、浪、雨的作用把沙粒带到农田里，在沙子覆盖的沿岸地带建防风林能减少这种情况发生，本题表述与原文相符。
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