大学英语六级听力练习 012

Disappearing Forests

The world's forests are disappearing.As much as one third of the total tree cover has been lost.Since agriculture began some ten thousand years ago.The remaining forests are home to half of the world's species,thus becoming the chief resource for their survival.Tropical rain forests once covered 12% of the land of the planet.As well as supporting at least half of the world's species of plants and animals，these rainforests are home to millions of people.

But there are other demands on them,as well.For example，much wood has been cut for timber.An increasing amount of forest land has been used for industrial purposes or for agriculture development such as crop growing.By the 1990s less than half of the earth's original rain forests remained，and they continued to disappear at an alarming rate every year.As a result，the world's forests are now facing gradual extinction.