TPO 1-3 Timberline Vegetation on Mountains

The transition from forest to treeless tundra on a mountain slope is often a dramatic one.

The transition from forest to treeless tundra on a mountain slope is often a dramatic one.

The transition from forest to treeless tundra on a mountain slope is often a dramatic one.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Species of birch, for example, may occur at the timberline in parts of the Himalayas.

Species of birch, for example, may occur at the timberline in parts of the Himalayas.

Species of birch, for example, may occur at the timberline in parts of the Himalayas.

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 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 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 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.

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.

This is because middle- and upper- latitude timberlines are strongly influenced by the duration and depth of the snow cover.

This is because middle- and upper- latitude timberlines are strongly influenced by the duration and depth of the snow cover.

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.

Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.

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.

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.

Various environmental factors may play a role.

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.

Too much snow, for example, can smother trees, and avalanches and snow creep can damage or destroy them.

Too much snow, for example, can smother trees, and avalanches and snow creep can damage or destroy them.

Too much snow, for example, can smother trees, and avalanches and snow creep can damage or destroy them.

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.

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.

Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.

Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.

Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.

Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

In an area where low temperatures are limiting to life, the importance of the additional heat near the surface is crucial.

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.

The word “dramatic” in the passage is closest in meaning to ○gradual ○complex ○visible ○striking 2.

The word “dramatic” in the passage is closest in meaning to ○gradual ○complex ○visible ○striking 2.

The word “dramatic” in the passage is closest in meaning to ○gradual ○complex ○visible ○striking 2.

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

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

Which of the following can be inferred from paragraph 1 about both the upper and lower timberlines?

○Both mark forest boundaries.

○Both are surrounded by desert areas.

○Both suffer from a lack of moisture.

○They cannot grow in cold climates.

○They do not exist at the upper timberline.

○They do not require as much moisture as evergreens do.

The word “attain” in the passage is closest in meaning to ○require ○resist ○achieve ○endure 6.

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

In paragraph 4, what is the author’s main purpose in the discussion of the dramatic cessation of tree growth at the upper timberline?

In paragraph 4, what is the author’s main purpose in the discussion of the dramatic cessation of tree growth at the upper timberline?

○To argue that none of several environment factors that are believed to contribute to that phenomenon do in fact play a role in causing it.

○To argue in support of one particular explanation of that phenomenon against several competing explanations

○To argue in support of one particular explanation of that phenomenon against several competing explanations

○To explain why the primary environmental factor responsible for that phenomenon has not yet been identified

○To explain why the primary environmental factor responsible for that phenomenon has not yet been identified

○To explain why the primary environmental factor responsible for that phenomenon has not yet been identified

○To explain why the primary environmental factor responsible for that phenomenon has not yet been identified

○To present several environmental factors that may contribute to a satisfactory explanation of that phenomenon

The word “prevalent” in the passage is closest in meaning to ○predictable ○widespread ○successful ○developed 12.

The word “prevalent” in the passage is closest in meaning to ○predictable ○widespread ○successful ○developed 12.

Look at the four squares [█] that indicate where the following sentence could be added to the passage.

Directions: An introductory sentence for a brief summary of the passage is provided below.

Directions: An introductory sentence for a brief summary of the passage is provided below.

Directions: An introductory sentence for a brief summary of the passage is provided below.

Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage.

Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage.

At the timberline, whether upper or lower, there is a profound change in the growth of trees and other plants.

○The temperature at the upper timberline is probably more important in preventing tree growth than factors such as the amount of snowfall or the force of winds.

○The geographical location of an upper timberline has an impact on both the types of trees found there and their physical characteristics.

○The geographical location of an upper timberline has an impact on both the types of trees found there and their physical characteristics.

○The geographical location of an upper timberline has an impact on both the types of trees found there and their physical characteristics.

○High levels of ultraviolet light most likely play a greater role in determining tree growth at the upper timberline than do grazing animals such as the ibex.