托福閱讀30天備考之備考練習第五天

　　TPO 2 PASSAGE 1 TIMBERLINE VEGETATION ON MOUNTAINS 樹木分界線 【TPO原文】

　　1) Timberline trees are normallyevergreens, suggesting that these have some advantage over deciduous trees (those that lose their leaves) in the extreme environments of the upper timberline. (A比B有優(yōu)勢---兩者比較，容易出題)

　　2) This is particularly true fortrees in the middle and upper latitudes, which tend to attain greater heightson ridges, whereas in the tropics the trees reach their greater heights in the valleys.(whereas 的轉折信息，成為很多同學做題失分的原因)

　　3) As the snow is deeper and lasts longer in the valleys, trees tend to attain greater heights on the ridges, even though they are more exposed to high-velocity winds and poor, thin soils there. In the tropics, the valleys appear to be more favorable because they are less prone to dry out, they have less frost, and they have deeper soils. (寒冷地區(qū)和熱帶地區(qū)比較信息成為出題點。)

　　4) Late-lying snow reduces the effective growing season to the point where seedlings cannot establish themselves. (late-lying 積雪， establish扎根)

　　5) 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. (原因類的學術表達)

　　6) This enables them to avoid the worst rigors of high winds and permits them to make use of the highertemperatures immediately adjacent to the ground surface.