Since the rain forest is full of green plants,you may think that crops can also grow well there; but when the forest is cleared for farming,the soil changes suddenly and greatly.If the tropical,lowland rain forest (热带低地雨林),like what fills the Amazon basin of South America,is destroyed,the soil will generally become very barren in one year.
One reason the rain forest is so poor is that most of the nutrients are stored in the plants themselves.In most forests,dead organic matter (有机物) falls to the ground,providing valuable nutrients for new growth.In cooler or drier weather,the nutrients in the soil become larger in number.But in a rain forest,with its abundance and variety of life,those nutrients are reabsorbed almost as fast as they’re deposited (使沉淀).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 plants.Grass may grow for a year,but as the grass is turned into beef,the few remaining nutrients are used up.
Since land in the rain forest is cheap,farmers often clear new fields each year,leaving the old ones to turn into desert.
【解题导语】 雨林茂密的绿色植物让人们觉得那儿的土壤一定非常肥沃,然而,事实却并非如此。
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