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  3. Conventional wisdom says trees are good for the environment. They absorb carbon dioxide—a greenhouse gas—from the atmosphere and

Conventional wisdom says trees are good for the environment. They absorb carbon dioxide—a greenhouse gas—from the atmosphere and

admin2012-02-12  42
问题     Conventional wisdom says trees are good for the environment. They absorb carbon dioxide—a greenhouse gas—from the atmosphere and store it as carbon while releasing oxygen, a process for which forests have been called "the lungs of the planet". The roots of trees have been thought to trap sediments and nutrients in the soil. Trees have also been credited with steadying the flow of these rivers, keeping it relatively constant through wet and dry seasons, thus preventing both drought and flooding. It is all nonsense, concludes a research published this week. A four-year international study led by researchers at the University of Newcastle, in Britain, and the Free University of Amsterdam, identifies several myths about the link between forests and water. For example, in arid and semiarid areas, trees consume far more water than they trap. And it is not the trees that catch sediments and nutrients, and steady the flow of the rivers, but the fact that the soil has not been compressed.
    The World Commission on Water estimates that the demand for water will increase by around 50% in the next 30 years. Moreover, around 4 billion people—one half of the world’s population—will live in conditions of severe water stress, meaning they will not have enough water for drinking and washing to stay healthy, by 2025.
    The government of South Africa has been taking a tough approach to trees since it became the first to treat water as a basic human right in 1998. Trees lose water through evaporation (the technical term is transpiration) at twice the rate of grassland or South Africa’s unique fynbos scrubland. In a scheme praised by the hydrologists, the state penalizes forestry companies for preventing this water from reaching rivers and underground aquifers.
    In India, large tree-planting schemes not only lose valuable water but complicate the true problem identified by the hydrologists; the unregulated removal of water from aquifers to irrigate crops. Fanners need no permit to drill a borehole and, as most farmers receive free electricity, there is little economic control on the volume of water pumped. In the Kolar district in Karnataka, wells have dried up as the water table has plummeted from six metres to 150 metres below ground. Summary:
    It is commonly believed that trees are good for the environment, as they absorb carbon dioxide and release oxygen; the roots of trees can trap water and【41】______ the flow of rivers. However, a recent study has found that this belief is【42】______.
    According to the research, trees lose【43】______ water through evaporation than they trap. In South Africa, forestry companies are punished as the trees they planted prevented water from【44】______rivers and underground aquifers. In India, farmers drilled many wells and used the underground water to【45】______their farmland. This has lowered water table to 150 metres below ground. Many trees have been planted and in fact these trees complicate the existing problem.
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解析 由文章可知树木有时消耗的水分比所留下的多得多。
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