Hot-dry valleys are widely distributed in subtropical zone of China. For example, Red River, Lanchang River, Nu River  Jingsha River, Yanong River,Ming River and so on, as well as their branches, are all characterized by the climate of hot-dry valley. After premerial monsoon rain forests were destroyed, the landscope of secondary grassland with sparse woods apeared. In generally, grass is 20-30 cm high, percentage of grass cover is 30-40%. Water and soillose seriously, soillayer is thin and poor. The ecosystem becomes worse, the ability of preventing the hazards decreases.

Due to natural force and human activity , erosion and transporation are enhanced. The mountain hazards ,such as debris flow ,occur frequently. For instance, the 40km-long highway from Duge to Laomu-River electric station in Lingnan, Liangshan, Sichuan line with 20 debris flow ravines. So it is trouble to construct in mountain areas. There are 41 poor-counties total in Yunnan Province , and 10 of them are in hot-clry valley in Jingsha River. So it is an important task for the hot-dry valley areas to administrate，exploit and break away from poor.

 

If the vegetation in slope will be restored as soon as possible, the environment will be imporved and the administation will be accelarated , debris flow and othcr hazards will be reduced or be brought under permanent control. Just mention two provinces -- Sichuan and Yunnan, 5 debris flow ravines were tackled in a comprehensive way. The social, economical and ecological benefit was notable. For a typical instance , after Heisha River, Xichang, Sichuan was administrated, percentage of forest cover increased from 2. 7 % to 74% , 133ha debris flow wasteland were changed to farmland. People planted mulberry and raised silkworms. The income only in sericulture was over 10 million
yuan in 1991.