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  3. Rain forests Did you know there are two types of Rainforest-the temperate and the tropical? Tropical rainforests are found c

Rain forests Did you know there are two types of Rainforest-the temperate and the tropical? Tropical rainforests are found c

admin2010-04-12  40
问题                        Rain forests
    Did you know there are two types of Rainforest-the temperate and the tropical? Tropical rainforests are found close to the equator. Temperate rainforests are found along coasts in the temperate zone, such as the Pacific Northwest of the USA. Both are endangered!
    Rainforests Endangered!
    Today only about three percent of the original temperate rainforest in the U. S. A. remains, mostly inside Olympic National Park in Washington State. Prior to the arrival of homesteaders just over a century ago, the Olympic Peninsula contained more than a million acres of old-growth spruce and hemlock. Because of habitat destruction, many plants and animals have become "island dwellers" inside the park now.
    Tropical rainforests comprise only 40% of the world’s tropical forests and only 20% of the world’s total forests. They cover 6%-7% of the Earth’s land surface. Half of the world’s plant and animal species live in the tropical rainforests of the world. Thirty acres of trees are cut in the tropical rainforests every minute. As you read this, tropical rainforests are shrinking. Each second a portion of rainforest the size of a football field is destroyed or damaged.
    What Makes the Tropical Rainforest Special?
    The rainforests are home to half of the Earth’s plant and animal species.
    They are winter homes to many birds that breed in temperate latitudes.
    Tropical rainforests are some of the most beautiful wildernesses on our planet.
    They are home to tribal cultures that have survived successfully in the forests for many thousands of years.
    The forests are a potential source of medicinal plants that may benefit everyone on Earth.
    The ecosystem of the rainforest is based on the most complex interdependence of plants and animals.  This is both the forest’s strength and its weakness: highly specialized organisms are particularly vulnerable to disturbance, because they cannot adapt fast enough to survive the change.
    Tropical rainforests help maintain global rain and weather patterns. Much of the water that evaporates from the trees returns in the form of rainfall. Removal of the forest can change the natural rainfall patterns.
    Tropical Rainforest Layers
    Tropical rainforests have four layers:
    Emergent Layer
    These giant trees thrust above the dense canopy layer(树冠层) and have huge mushroom-shaped  crowns. These trees enjoy the greatest amount of sunlight but also must endure high temperatures, low humidity, and strong winds.
    Canopy Layer
    The broad, irregular crowns of these trees form a tight, continuous canopy 60 to 90 feet above the ground. The branches are often densely covered with other plants (epiphytes) and tied together with vines (lianas). The canopy is home to 90% of the organisms found in the rain forest; many seeking the brighter light in the treetops.
    Understory
    Receiving only 2%-15% of the sunlight that falls on the canopy, the understory is a dark place. It is relatively open and contains young trees and leafy herbaceous plants that tolerate low light. Many popular house plants come from this layer. Only along rivers and roadways and in tree fall and cut areas is sunlight sufficient to allow growth to become thick and impenetrable
    Forest Floor
    The forest floor receives less than 2% of the sunlight and consequently, little grows here except plants adapted to very low light. On the floor is a thin layer of fallen leaves, seeds, fruits, and branches that very quickly decomposes. Only a thin layer of decaying organic matter is found, unlike in temperate deciduous(落叶性的) forests.
    Soil and Nutrient Recycling
    Most tropical rainforest soils are relatively poor in nutrients. Millions of years of weathering and torrential rains have washed most of the nutrients out of the soil. More recent volcanic soils, however, can be very fertile. Tropical rain forest soils contain less organic matter than temperate forests and most of the available nutrients are found in the living plant and animal material. Nutrients in the soil are often in forms that are not accessible by plants.
Constant warmth and moisture promote rapid decay of organic matter. When a tree dies in the rainforest, living organisms quickly absorb the nutrients before they have a chance to be washed away. When tropical forests are cut and burned, heavy rains can quickly wash the released nutrients away, leaving the soil even more impoverished.
    Causes of Destruction
    Tropical rainforests are being cut at an alarming rate.  Although estimates vary, some scientists believe that we are losing an area of rainforest the size of Pennsylvania each year. If deforestation continues at this rate we may lose rainforests altogether within the next one hundred years.
    Tropical deforestation occurs for a number of reasons. As human populations increase in tropical regions, people move away from the overcrowded cities into the forest areas where they practice small-scale farming. Commercial agricultural projects may require conversion of large plots of rainforest land and may cause more permanent damage.
    Logging of forests for firewood, charcoal, building materials, and other wood products is another cause of deforestation.
    The conversion of rainforest to pasture land for cattle ranching has led to the destruction of millions of acres of forest.
    Mining for gold, bauxite from which aluminum is made, and other minerals can lead to the drastic destruction of the land. Once the land is scarred by mining efforts it is left vulnerable to massive erosion.
    Other events and issues such as natural disasters, war, the construction of dams, and poverty in developing countries also contribute to the destruction of tropical rainforests.
What Can You Do to Help Save the Tropical Rainforest?
    Preserving tropical rainforests involves more than just deciding not to cut trees. Social, political and economic factors all need to be taken into consideration. The following are some suggestions about how you can contribute to the solution.
    Learn more about tropical rainforests and the plants and animals, including people, which live there. Investigate the complex issues surrounding deforestation and possible solutions through further reading.
    Write letters to your congressional representatives or your local paper to express concern about the destruction of the tropical rainforests. The more you know about the topic and issues, the more specific you can be in suggesting actions you would like your elected officials to take.
    Visit tropical countries to see the rainforest. Gaining firsthand experience is one of the best ways to develop an understanding of and commitment to an issue.
    Work to protect tropical rainforests and their indigenous peoples.
    Think globally and act locally. Practices at home, like the ones listed below, can have an impact on the preservation of rainforests.
    Recycling aluminum cans reduces the need for bauxite, which must be mined from the ground in tropical countries. Bauxite is the source of aluminum.
    Buy only pets which were captive bred here in the United States. Those which were not bred here may have been taken from the wild and imported illegally from tropical countries.
    When purchasing tropical woods for furniture or construction, investigate the source of the wood to determine whether it was grown in a sustainable  manner.
    In all things you do, practice the environmentally sound use and reuse of our resources. This will not only have a positive impact on the tropical rainforest but on all the ecosystems of the world.
The giant trees above the dense canopy layer(树冠层) cannot enjoy sunlight.
选项 A、Y
B、N
C、NG
答案B
解析  在文章的“Emergent Layer”一段中说道；“These giant trees thrust above the dense canopy layer(树冠层)and have huge mushroom-shaped crowns．  These trees enjoy the greatest amount of sunlight but also must endure high temperatures，low humidity，and strong winds。”从中得知，树冠层之上的这些大树是可以充分享受到阳光的。故答案为No。
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