【答案解析】Tibet boasts 7.17 million ha. of forest, and the stocking volume has reached 2.091 billion cum. Tibet has the largest primitive forest in China. To protect Tibet's ecological environment, the government exercises a "felling by quota" policy, and strictly controls the scale of tree-felling in forests. The annual felling amount for commercial purpose is limited to 150,000 cu m. // Simultaneously, a rotation system is in place for lumbering bases so as to help restore vegetation. A project for the protection of natural forest resources on the upper reaches of the Yangtze River in Tibet, with a total area of 31,000 sq kin, has been implemented in the three counties of Jomda, Gonjo and Markam that have a weighty bearing on the ecology of the lower Yangtze valley. // In 28 counties along the upper reaches of the Jinsha, Lancang and Nujiang rivers and the catchment area of the Yarlungzangbo River, where the hazards of sandstorm and soil erosion are serious, a project to restore farmland to forest is being undertaken, under which 52,000 ha. of cultivated land will be restored to forest and trees planted on 53,000 ha. of barren mountains and wasteland. //By 2002, some 6,700 ha. of cultivated land had been restored to forest and 6,700 ha. of barren mountains and wasteland afforested. The government is also striving to promote the development of energy substitutes and fuel forests, and popularize solar energy in order to protect natural bush vegetation. // It has become the conscious action of the Tibetan people to join afforestation efforts. The government of the Tibet Autonomous Region has formulated the "Forestation Plan of the Tibet Autonomous Region" and the "Opinions on Acceleration of Afforestation." The people of the whole region are making efforts by starting with the improvement of their living environments, first of all by greening their courtyards, streets and urban environment in general, and eventually building green belts in river catchment areas where human activities are concentrated, and along major highways. The results have been remarkable. // According to a survey, over the past 50-plus years some 70,000 ha. of land have been afforested in Tibet, 90 million trees have been planted beside villages, houses, roads and waterways, and 1.5 million cash trees have been grown. // Afforestation and ecological projects have been launched steadily. Implementation of the key projects, such as the afforestation project in Lhasa and its outskirts, the construction of the shelter-forest system of the Yarlungzangbo River, the pilot project of the Yangtze River shelter-forest system in Markam and the pilot project for controlling sand by afforestation in Xigaze, has, to a great extent, improved the natural eco-environment of those localities. // Since 1996, the State has begun to build a shelter-forest system along the upper and middle reaches of the Yangtze River. By 2000, it had invested more than 3.7 million yuan in the project, actively supporting Tibet in building man-made forests and sealing off mountainous areas to facilitate afforestation as appropriate to local conditions. The afforested area has topped 13,000 ha, which, as a result, has played a positive role in improving local residents' working and living conditions. //Following implementation of the project tot the construction of the shelter-forest system of the Yarlungzangbo River, which is part of the key "three rivers" agricultural development undertaking, a man-made forest belt measuring several hundred km. from Xigaze to Zetang on the upper reaches of the Yarlungzangbo River has been formed. Now, a new spectacular scene, the belt plays a positive role in conserving water and topsoil along the Yarlungzangbo River. // Due to the effective protection of natural forest resources and afforestation, the forest coverage in Tibet has kept growing. It has grown from less than 1% in the 1950s to 5.93% today, and has played a positive role in improving the Autonomous Region's ecological environment. // According to reports from relevant monitoring departments, due to the increase in man-made vegetation, the number of sandstorm days has decreased noticeably in Tibet. Currently. it is 32 days fewer in Lhasa, 34 days fewer in Xigaze and 32 days fewer in Zetang, than 30 years ago. // (Excerpts from the English version of the White Paper "Ecological Improvement and Environmental Protection in Tibet" issued by the Information Office of the State Council of PRC in March 2003)