在许多半干旱的地区中，同样存在树带界限的下限区域；在这片区域之内，由于缺乏水分，森林下沿区域的植被通常会逐渐变成干草原或沙漠。
In many semiarid areas there is also a lower timberline where the forest passes into steppe or desert at its lower edge, usually because of a lack of moisture.
如果森林变成了沙漠，它会反射更多的阳光并且让气温降下来。
If you turn a forest into a desert, it reflects more sunlight and makes it cooler.
将来某一天，这里可能绿树成荫...最近一篇科学报告声称，把沙漠变成森林是最好的解决办法。
One day, this could all be trees … a recent scientific paper claims that turning deserts into forests is the best way forward. Photograph: Guido Cozzi/Corbis
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