对于准备考托福的同学们来说,不知道准备得怎么样呢?今天就和出国留学网的小编一起来看看TPO阅读TPO1-3 Timberline如何用于托福写作?
素材原文
There is still no universally agreed-on explanation for why there should be such a dramatic cessation of tree growth at the upper timberline. Various environmental factors may play a role. Too much snow, for example, can smother trees, and avalanches and snow creep can damage or destroy them. Late-lying snow reduces the effective growing season to the point where seedlings cannot establish themselves. Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes. Some scientists have proposed that the presence of increasing levels of ultraviolet light with elevation may play a role, while browsing and grazing animals like the ibex may be another contributing factor. Probably the most important environmental factor is temperature, for if the growing season is too short and temperatures are too low, tree shoots and buds cannot mature sufficiently to survive the winter months.
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。多种环境因素都起到作用,例如,积雪过多会让树木透不过气,雪崩和雪移能摧毁树木;长时间积雪缩短了有效生长季节的时间,树苗无法生长;另外,风速会随着海拔的升高而增加,增加树木承受的压力,很明显,正是这种风速带来的压力导致树木在高纬度地区发生变形。一些科学家提出,随着海拔的上升而不断增强的紫外线、野生山羊等动物的放养,都是导致树带界线形成的因素。或许最重要的环境因素是温度,因为如果生长季节太短并且气温太低,树芽和树苗都无法充分地成长而存活过冬季。
素材结构
There is still no universally agreed-on explanation for why 给出问题. V...