托福TPO1阅读真题原文及答案翻译part3

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阅读真题原文及答案翻译

part3

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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 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.

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.

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.

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.

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.

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.

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 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.

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阅读真题题目

Part3

1. The word

○gradual

○complex

○visible

○striking

2. Where is the lower timberline mentioned in paragraph 1 likely to be found?

○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.

3. 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 desert 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 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.

4. Paragraph 2 supports which of the following statements about deciduous

trees?

○They cannot grow in cold climates.

○They do not exist at the upper timberline.

○They are less likely than evergreens to survive at the upper timberline.

○They do no

t require as much moisture as evergreens do.

Paragraph 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.

5. The word

○require

○resist

○achieve

○endure

6. The word

○valleys

○trees

○heights

○ridges

7. The word

○adapted

○likely

○difficult

○resistant

8. According to paragraph 3, which of the following is true of trees in the middle

and upper latitudes?

○Tree growth is negatively affected by the snow cover in valleys

○Tree growth is greater in valleys than on ridges.

○Tree growth on ridges is not affected by high

-velocity winds.

○Tree growth lasts longer in those latitudes than it does in the tropics.

Paragraph 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