TPO是托福备考圣经，但是并不是有“圣经”就能完全把握托福考试。还要看大家怎么去利用这份资料。关于TPO阅读，托福小编希望最大限度地利用这些ETS提供的阅读文章。在文章中，找到那些生词，长难句；分析文章结构。真正把它作为一份备考资料，而不是做题工具。今天小编分享给大家的是对TPO1 Timberline Vegetation on Mountains的文章详细分析。一起学习吧！
Timberline Vegetation on Mountains
山上树带界线的植被
1.The transition from forest to treeless tundra on a mountain slope is often a dramatic one. Within a vertical distance of just a few tens of meters, trees disappear as a life-form and are replaced by low shrubs, herbs, and grasses. This rapid zone of transition is called the upper timberline or tree line. 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.
通常从山坡上的森林到没有树的苔原是一种非常戏剧化的转变。在一个垂直距离只有几十米的地方，树木这种生命形式就消失了，取而代之的是低矮的灌木、草本植物和牧草。这种快速过渡的区域被称为上行树带界线或林木线。在许多干旱的地区存在着下行树带界线，在这里由于缺乏水分森林变成干草原，甚至在最下端会出现沙漠。
上行树带界线的定义。
2.The upper timberline, like the snow line, is highest in the tropics and lowest in the Polar Regions. It ranges from sea level in the Polar Regions to 4,500 meters in the dry subtropics and 3,500-4,500 meters in the moist tropics. Timberline trees are normally evergreens, suggesting that these have some advantage over deciduous trees (those that lose their leaves) in the extreme environments of the upper timberline. There are some areas, however, where broadleaf deciduous trees form the timberline. Species of birch, for example, may occur at the timberline in parts of the Himalayas.
上行树带界线，和雪线一样，在热带最高，在极地最低。从极地地区的海平面到干燥的亚热带地区的海拔4 500米处以及潮湿的热带地区海拔3 500米至4 500米处都有上行树带界线。树带界线内通常是常绿树，它们和处于上行树带界线处极端恶劣环境中生长的落叶树木相比，具有一定的优势。然而，在部分地区也有由落叶阔叶林组成的树带界线。例如，在喜马拉雅的部分地区，桦树就在树带界线上。
树带界限生长的树木类型。
3.At the upper timberline the trees begin to become twisted and deformed. This is particularly true for trees in the middle and upper latitudes, which tend to attain greater heights on ridges, whereas in the tropics the trees reach their greater heights in the valleys. This is because middle- and upper- latitude timberlines are strongly influenced by the duration and depth of the snow cover. 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.
上行树带界线的树木开始扭曲和变形，尤其在中高纬度地区的树木，这些地区的树木往往会在山脊上长得更高，而在热带地区的树木则在山谷里长得更高；因为中高纬度地区树带界线受积雪覆盖时间和深度的影响很大。由于山谷中积雪覆盖较厚且持续时间很长，树木即便是生长在大风和贫瘠的土地里，也往往会在山脊上长得更高。在热带地区山谷里更有利于生长，因为山谷不易干涸、很少结霜，并且有更深的土壤。
上行树带界线的树木生长状况及环境特点。
4.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。
树带界线上出现树木停止生长现象的多种环境因素。
5.Above the tree line there is a zone that is generally called alpine tundra. Immediately adjacent to the timberline, the tundra consists of a fairly complete cover of low-lying shrubs, herbs, and grasses, while higher up the number and diversity of species decrease until there is much bare ground with occasional mosses and lichens and some prostrate cushion plants. Some plants can even survive in favorable microhabitats above the snow line. The highest plants in the world occur at around 6,100 meters on Makalu in the Himalayas. At this great height, rocks, warmed by the sun, melt small snowdrifts.
在林木线之上有一个称为高山苔原的地带。由于紧挨着树带界线，苔原上都是矮灌木、草本植物和牧草。随着海拔的增加，物种的数量和多样性会逐渐减少，直到出现大量空地伴着零星的苔藓和地衣这样的伏地垫状植物。有些植物甚至可以在雪线以上有利的微环境中生存，世界上海拔最高的植物是出现在喜马拉雅山上6 100百米的马卡鲁峰。在这个高度上，被阳光温暖过的岩石可以将小雪堆融化。
6.The most striking characteristic of the plants of the alpine zone is their low growth form. This enables them to avoid the worst rigors of high winds and permits them to make use of the higher temperatures immediately adjacent to the ground surface. In an area where low temperatures are limiting to life, the importance of the additional heat near the surface is crucial. The low growth form can also permit the plants to take advantage of the insulation provided by a winter snow cover. In the equatorial mountains the low growth form is less prevalent.
高山植物最突出的特点是其低矮的生长形态。这种特点使他们能够避开大风最强势的势头，并且有助于他们利用紧邻地面相对较高的温度。在这样一个低温限制生命的地区，地表提供的额外温度是至关重要的。低矮的生长形态也可以帮助植物充分利用冬季积雪所提供的保温环境。在赤道区的山脉上低矮的生长形态并不常见。
在林木线之上的高山苔原地带的植物生长状况及环境特点。
疑难词：
dramatic adj. 戏剧的；引人注目的；激动人心的
vertical n. 垂直线，垂直面adj. 垂直的
deciduous adj. 落叶性的
cessation n. 停止；中止；中断
elevation n. 高地；海拔
smother vt. 使窒息；抑制vi. 窒息；被抑制
velocity n. 速率，速度
Striking adj. 显著的，突出的，惊人的
长难句：
1.This is particularly true for trees in the middle and upper latitudes, (which tend to attain greater heights on ridges), whereas in the tropics the trees reach their greater heights in the valley.
句子类型：which引导的非限制性定语从句
结构拆分：
主干：This is true for…
定语从句：which tend to attain greater heights on ridges，which的先行词是trees
让步状语从句：whereas in the tropics the trees reach their greater heights in the valley，whereas引导的句子表转折
翻译：尤其对于那些在山脊上会长的更高的中高纬度地区的树木(更为适用)，而在热带地区的树木在山谷里长的更高。
2.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.
句子类型：原因状语从句+让步状语从句
句子拆分：
主干：trees tend to attain greater heights.
原因状语从句：As the snow is deeper and lasts longer in the valleys,
让步状语从句：even though they are more exposed to high-velocity winds and poor, thin soils there.
翻译：由于山谷中积雪覆盖较厚且持续时间很长，树木即便是生长在大风和贫瘠的土地里，也往往会在山脊上长得更高。
3.At this great height, rocks, warmed by the sun, melt small snowdrifts.
句子类型：插入语
句子拆分；
主干：rocks melt small snowdrifts
插入语：warmed by the sun修饰rocks
翻译：在这个高度上，被阳光温暖过的岩石可以将小雪堆融化。
4.This enables them to avoid the worst rigors of high winds and permits them to make use of the higher temperatures( immediately adjacent to the ground surface).
句子是and结构，由两个带宾语补足语结构的句子构成。
主干：This enables them to avoid…and permits them to make use of…
翻译：这种特点使他们能够避开大风最强势的势头，并且有助于他们利用紧邻地面相对较高的温度。
文章架构：
第1段：上行树带界限的定义。
第2.3.4段：树带线上的环境特点、植物的生长特征及环境原因。
第5.6段：给出一个高山苔原高山苔原的地带的定义，以及这个地带植物生长的特点以及环境原因。
文章题材：
环境科学—植物与环境
以上就是关于TPO1 Timberline Vegetation on Mountains的文章分析，希望对大家的备考有所帮助，前程百利祝大家都能取得理想的托福考试成绩。
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