Лекция: Desertification: A Serious and Growing Problem

The conversion of rangeland (uncul­tivated land used for animal graz­ing), rain-fed cropland, or irrigated cropland to desertlike land with a drop in agricultural productivity of 10% or more is called desertifica­tion. Moderate desertification causes a 10% to 25% drop in productivity; severe desertification causes a 25% to 50% drop; and very severe deser­tification causes a drop of 50% or more and usually the formation of massive gullies and sand dunes.

Prolonged drought and hot temperatures may accelerate the desertification process. But its basic causes are overgrazing of rangeland by concentrating too many livestock on too little land area; improper soil and water resource management that leads to increased erosion, sal-inization, waterlogging, cultivation of marginal land with unsuitable terrain or soils, and deforestation and strip mining without adequate replanting.

Each year, the amount of deser­tified land grows by at least 20 mil­lion hectares (49 million acres)—an area equal to that of South Dakota. According to the UN Environmental Programme, one-fifth of the world's people now live in areas that may become desertified over the next 20 years.

The spread of desertification can be halted or sharply reduced by improved management of rangeland, forest, soil, and water resources, and much currently desertified land can be reclaimed. The total cost of such prevention and rehabilitation would be about $141 billion. Although this amount may seem staggering, it is only five and one-half times the estimated $26 billion annual loss in agricultural productivity from desertified land. Thus once this potential productiv­ity is restored, the costs of the pro­gram could be recouped in five to ten years. However, funds now devoted to preventing desertifica­tion and restoring desertified lands fall far short of the need.

Упражнение 12.

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