Imagine living on the edge of a vast desert, which is moving quietly closer to your village every day and covering your fields. The desert is on the move. This is called desertification.
Desertification occurs in regions close to an already existing desert. It generally arises from two related causes. The first is over-use of water in the area. There is not enough water in any case, and if it is not carefully used, disaster can follow. As time goes on, water shortages make farming more and more difficult. In some places, locals can remember local lakes and marshes which were once the homes for all kinds of fish and birds. They have been completely buried by the sand now. Farmers leave the land, and fields are replaced by deserts.
The second cause is misuse or over-use of the land. This means that the wrong crops are planted and need more water than is available. Ploughing large fields and removing bushes and trees means that the wind will blow away the soil. Once the soil is lost, it is hard to replace, and if there is rain, it has nowhere to go, and brings no benefit.
It is not only the farmers and villagers who suffer. Every spring, the skies over some of eastern cities, thousands of kilometers away from the deserts, can be darkened by sandstorms. Dust from deserts can have a great effect on weather systems. While desertification is perhaps being partly caused by global warming, these sandstorms can make global warming worse by adding to what is known as the greenhouse effect.
What can be done to slow down or stop the process of desertification? A great deal of work is already under way. Obviously first steps are to find new water sources. Tree planting can help, by providing barriers between desert and rich field. Some types of grass also hold the soil together, and stop the wind taking it. Without these efforts, it will be harder and harder to stop the world’s deserts in their tracks, and more and more farmers will give up and head for cities. The lesson to be learnt lies beneath the sand.
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Whenever human populations have lived in forest areas, they have always cut down trees which they used for a number of purposes, for housing and ships and served as a source of heating fuel and timber. Growth of cities often meant expansion into forest areas, while even more trees were removed to provide space for agriculture. With the growing demand for paper, vast quantities of trees have also been cut down for paper production. These factors, along with many others, have been contributing to a dangerous phenomenon known as deforestation.
In the last 5,000 years, humans have reduced forest from roughly 50 percent of the earth’s land surface to less than 20 percent. Most of this original, or old growth, forest cover is concentrated in three large areas: the Canadian and Alaskan boreal forest, the boreal forest of Russia, and the tropical forest of the northwestern Amazon Basin and the Guyana Shield. These areas comprise almost 70 percent of the world’s remaining original forest cover. In most places, the rate of deforestation is increasing, with the alarming result of 16 million hectares disappearing worldwide every year.
Loss of forest does not just mean the decline of natural resources. There are several other factors that make deforestation seriously harmful to both the human and natural worlds. One of them is changes in the global climate. For example, forest clearance is releasing substantial volumes of carbon dioxide (CO2) into the atmosphere as vegetation is burnt or decays. It has been suggested that this is a significant factor in global warming. Moreover, about 10 percent of the world’s tree species are in danger of extinction as a result of deforestation. Deforestation also threatens biological diversity through the destruction of wildlife habitats, which endangers a number of animal species and leads to their potential disappearance. Species are particularly easy to extinction in tropical rainforests because many species have few individuals per unit area, which makes reproduction more difficult. Finally, since forests play an important role in storing water and stabilizing soil, deforestation and the resulting change in land use cause soil erosion(腐蚀) and other forms of land degradation.
1. The passage discusses all of the following EXCEPT the ________.| A．causes of deforestation | B．consequences of deforestation |
| C．management of deforestation | D．rate of deforestation |
| A．variety | B．expansion |
| C．development | D．advantage |
| A．To explain the rate of deforestation. |
| B．To compare them with housing and ships. |
| C．To show the dangers of deforestation. |
| D．To illustrate the causes of deforestation. |
| A．Deforestation threatens biological diversity. |
| B．Deforestation has many harmful consequences. |
| C．Deforestation causes changes in global climate. |
| D．Deforestation should be stopped. |
