【英语时差8,16】伐木致热带雨林土壤贫瘠（下）（在线收听）

In any forest, dead organic matter falls to the ground, providing valuable nutrients for new growth. In cooler or drier climates, the nutrients build up in the soil. But in a rain forest, with its abundance and variety of life, those nutrients are reabsorbed almost as fast as they’re deposited. Also, the trees in tropical rain forests are often evergreens and so very few leaves actually fall to the ground. When a rain forest is burned to raise crops or cattle, most of the nutrients are destroyed along with the vegetation. Grass may grow for a year, but as the grass is turned into beef, the few remaining nutrients are depleted. Since land in the rain forest is often cheaper than fertilizer, farmers often clear new fields each year, leaving the old ones to turn into desert.