“如果你砍倒的树比你种的还多，你就会将树用光，”基尔丁写道，“如果你将额外的氮投放进一个水系，你就会改变那个水体所能维持生命的种类和数量。

“If you cut down more trees than you grow, you run out of trees,” writes Gilding.“If you put additional nitrogen into a water system, you change the type and quantity of life that water can support.

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“如果你砍倒的树比你种的还多，你就会将树用光，”基尔丁写道，“如果你将额外的氮投放进一个水系，你就会改变那个水体所能维持生命的种类和数量。”

"If you cut down more trees than you grow, you run out of trees," writes Gilding. "if you put additional nitrogen into a water system, you change the type and quantity of life that water can support."

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某些种类的北极鸟受到近来雪雁数量急剧增加的威胁，这些雪雁在北极繁殖，并且正在取代生命力较弱的鸟类。

Some species of Arctic birds are threatened by recent sharp increases in the population of snow geese, which breed in the Arctic and are displacing birds of less vigorous species.

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