树线timberline/treeline，是指天然森林垂直分布的上限。
对于为什么树线以上的树木会突然停止生长，至今还没有一个公认的解释。
There is still no universally agreed-on explanation for why there should be such a dramatic cessation of tree growth at the upper timberline.
首先，我们已经改变了子树线。
为了揭示高山树线随着气候变化而变化的现象，对长白山的高山树线变化趋势进行了研究。
In order to decipher phenomenon of tree line changing with climate variety, the trend of tree line on the Northern Slope of Changbai Mountain was studied.
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