托福TPO1阅读真题原文及答案翻译part3
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托福TPO1阅读真题原文Part3
Timberline Vegetation on Mountains
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 grass. This rapid zone of transition is called the upper timberline or tree line. In many miarid areas there is also a lower timberline where the forest pass into steppe or dert at its lower edge, usually becau of a lack of moisture.
The upper timberline, like the snow line, is highest in the tropics and lowest in the Polar Regions. It ranges from a 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, sug
gesting that the have some advantage over deciduous trees (tho that lo 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.
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 becau 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 expod to high-velocity winds and poor, thin soils there. In the tropics, the valleys appear to be more favorable becau they are less prone to dry out, they have less frost, and they have deeper soils.
There is still no universally agreed-on explanation for why there should be such a dramati
c 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 ason to the point where edlings cannot establish themlves. Wind velocity also increas with altitude and may cau rious stress for trees, as is made evident by the deformed shapes at high altitudes. Some scientists have propod that the prence 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 ason is too short and temperatures are too low, tree shoots and buds cannot mature sufficiently to survive the winter months.
four letter word
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 grass, while higher up the number and diversity of species decrea until there is much bare ground with occasional moss and lichens and some
iamprostrate 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.
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 u 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.
Paragraph 1: The transition from forest to treeless tundra on a mountain slope is often adramatic 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 grass. This rapid zone of transition is called the upper timberline or tree line. In many miarid areas there is also a
gogoglelower timberline where the forest pass into steppe or dert at its lower edge, usually becau of a lack of moisture.
托福TPO1阅读真题题目Part3
1. The word "dramatic" in the passage is clost in meaning to
○gradual
○complex
○visible
domesticated○striking
2. Where is the lower timberline mentioned in paragraph 1 likely to be found?
amy是什么意思>英语幽默小短文○In an area that has little water
○In an area that has little sunlight
○Above a transition area
○On a mountain that has on upper timberline.
英语论文翻译lately3. Which of the following can be inferred from paragraph 1 about both the upper and lower timberlines?
○Both are treeless zones.
○Both mark forest boundaries.
○Both are surrounded by dert areas.
○Both suffer from a lack of moisture.
Paragraph 2: The upper timberline, like the snow line, is highest in the tropics and lowest in the Polar Regions. It ranges from a 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 the have some advantage over deciduous trees (tho tha
t lo 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.阿卡索外教网收费
