| Ecological environment is the basis of existence and development of human being. Loess Plateau is the origin of Chinese civilization, but it has degraded into a barren and fragile plateau with dense broken hills and gullies. Severe soil and water erosion as well as environmental degradation are hindering the sustainable development of economy and society in Loess Plateau and in the area of the middle and lower reaches of Yellow River. Rehabilitation of Ecological Environment (REE) in Loess Plateau is facing a precious chance with the campaigns of development of west China as well as greening up mountains and conservation of water and soil. With the advantageous location jointing east and west China, it is meaningful to rehabilitate ecological environment in Loess Plateau within Shaanxi Territory (LPST) because the rehabilitation is the example not only in all Loess Plateau, but also in northwest China.In this dissertation, firstly, the law of ecological environment's evolution and the previous theories about REE are reviewed. Then, based above, the new mode of REE and the concrete approach of REE in LPST are projected. Further more, the changing of land use and the balance between supply and demand of grain during Returning Farmland on Hills into Forest and Grassland (RFHFG) are discussed in detail by dividing LPST into four different parts. At last, the optimum mode and the compatible technological countermeasures of RFHFG are designed.The main conclusions of the study are as follows:The degradation of ecological environment in Loess Plateau is the result of inherent tectonic movement, climate, topography, configuration of the earth's surface and other natural factors, also improper reclamation and over-logging of mankind during the long historical period.REE in Loess Plateau is the rehabilitation of ecological system and the adjustment of ecological system structure to change the ill structure to rational one, as well as the process of regaining the requisite functions of ecological system. Essentially, REE is to harmonize the natural eco-system and social-economic-system in order to construct an artificial eco-system, which satisfies the demand of both social-economic-system and natural eco-system. All support strategies for building the artificial eco-system are the technological countermeasures for REE.The optimum scheme of RFHFG in LPST is the return of all farmland on ground sloping more than 25 degrees in LPST till the year of 2005, the return of all farmland on hills between 15 to 25 degrees in Weibei mesa part and Guanzhong plain part till the year of 2010 and the return of farmland sloping between 15-25 degrees in Sandy and windy Great-Wall part until 2020. But in Gully and hilly part, for the deficiencies of grain, the total of returned farmland sloping between 15-25 degrees depends on not only the decrease of grain demand by the control of population, but also the amount of grain that can be bought with the improvement of forestry, animal husbandry and other industries.There is obvious differentiation among the four parts in LPST during RFHFG. In Gully and hilly part, area of farmland needs to return is the most and its own grain is much less than its demand, so massive grain should be offered from central government and/or its counterparts. In Sandy and windy Great-Wall part, grain can satisfy at lower demand level and 28.19 percent of the total arable land needs to be returned. In Weibei mesa part, grain is enough at lower level, but neither the reforestation of 341.7 thousand hectares barren mountains nor the supply of grain for itself is an easy task. In Guanzhong plain, the main undertaking is to greatly reinforce grain production to support other parts in LPST.The project of RFHFG can be carried out in two stages. In the first stage, in LPST, cultivated land sloping more than 25 degrees should be returned by the year of 2005. In the coming five years from 2000 to 2005, 573.5 thousand hectares farmland should be returned, 28.7 thousand hectares farmland returned a year, 0.0... |
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