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  3. Desertification is the accumulated result of inappropriate land use and a harsh climate. Over-cultivation exhausts the soil, ove

Desertification is the accumulated result of inappropriate land use and a harsh climate. Over-cultivation exhausts the soil, ove

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问题     Desertification is the accumulated result of inappropriate land use and a harsh climate. Over-cultivation exhausts the soil, overgrazing leaves behind little vegetation that protects it from erosion, deforestation destroys the trees that bind the soil to the land and underdeveloped irrigation systems turn croplands salty. The semi-dry lands bordering desert exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. The causes are multiple and interact in a complex manner. Lacking alternative survival strategies, farmers tend to over-exploit natural resources. Soil nutrients and organic matter begin to diminish once intensive agriculture consumes quantities of nutrients greater than the soil’s natural regeneration capacities.
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答案 沙漠化是由于土地使用方式不当和恶劣的气候条件累积而成的。过度种植耗尽了土壤的养分，过度放牧使保护土壤免遭侵蚀的植被所剩无几，砍伐森林毁灭了起固土作用的树木，而落后的灌溉系统使农田变成盐碱地。沙漠周边的半干旱土地的生态平衡十分脆弱，而且对环境压力增加的适应力有限。沙漠化的原因多种多样、相互作用并十分复杂。由于缺少替代的生存手段，农民往往过度利用自然资源。一旦精工细作的农业消耗的营养物数量超出土壤自身的再生能力时，土壤的营养物和有机物就开始减少。
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