在树带界线的上限区域，树木开始弯曲变形。

At the upper timberline the trees begin to become twisted and deformed.

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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.

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目前还没有一个普遍认同的解释来说明为什么会在树带界线上出现树木停止生长这种戏剧化的现象。

There is still no universally agreed-on explanation fir why there should be such a dramatic cessation of tree growth at the upper timberline.

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