Abstract:

Based on the achievements of forest history, ecology, climatology and desertology, the relationships of forest, evapotranspiration, climate and desert were studied. The results showed that: the four things have close interrelations. The decrease of Chinese forests in large area owing to the activity of the mankind leads to the reduction of land evapotranspiration first. It makes the climate in North China getting to dry gradually then. As an end result, desert enlarges rapidly. In the past 4 000 years, forest coverage decreased from 60% to 12.5%. It as a main reason caused great reductions of both the total evapotranspiration for 146mm·a^-1 and the mean annual precipitation for 200mm, as well as enlargement of desert percentage taking territory from 10% to 17.6%. Forest and desert compose the two poles of land ecosystem. Their relations are one decrease at the same time another increase. The medium is water that links the two poles. The essential method to prevent and control the desertification in North China is to breed forests, named 'Cloud Origin Forests', in the southeast half part of China fitting for forests.

Key words: change of forest, evapotranspiration, precipitation, desertification, Cloud Origin Forests