| Jieba region which is located in ecotone between agriculture and animal husbandry, has its unique ecosystem vulnerability. It's the ecological barrier and an important water source area for Beijing and Tianjin. Meanwhile, It's also the major sand source area and sand channel of Beijing-Tianjin area. Due to the special geology geomorphology and natural conditions along with long-term excessive reclamation and over grazing, the ecological environment of this region became worse and worse. This is a serious threat to ecological security and production and life of local people in Beijing and Tianjin area. Therefore, it has a great significance to study the dynamic law of land desertification, vegetation types and its succession law for evaluating the implementation of ecological engineering project in this region. The results of this research would be laid an important guiding role in theory and practice of this research field.The research was mainly conducted in Xiaobazi Village of Fengning County from 2006 to 2009. In this study, the methods of satellite remote sensing image interpretation combining with ground recognition, and experimentation in plot combining with field investigation with the theory of restoration ecology and ecological engineering etc. were used to systematically analyze the source, causes and variation of desertified land, vegetation types and succession law, the change of land use, the distribution of soil biological crusts and the influence of different project methods on ecological restoration in Xiaobazi region.The results are as follows:(1) The laws and mechanisms of sand movement and formation of sand deposition in Xiaobazi. By geological features and climate factors, there are more and more sand sources and deposition or accumulation in Xiaobazi and its upper mountainous region. The land topography:narrow topography and climatic factors with irrational human economic activities and flood accelerate the formation of sand flow.(2) The great changes of land desertification and land use occurred in Xiaobazi.The type of land use which used to the arable land:extensive cultivation, deforestation and over grazing has been turned to the forest or grassland. The area of wood land, stocked land, young forest land and artificial grass land increased year by year. On the other hand, desertified land areas were under control or even decreased gradually from being widely expanded before. The degrees of desertification are gradually reduced now. This indicated that the changes of land use have affected positively the formation of sand and land desertification.(3) The forest communities in Xiaobazi can be divided into 4 vegetation types and 15 formations.Four vegetation types in the vertical structure of forest communities are boreal forest, deciduous broad-leaved forest, shrub and semi-deciduous shrub and grassland vegetation separately. It is an typical forest-grass transitional vegetation with rich vegetation types, complex plant composition and a significant transition.(4) Ecological engineering measures could significantly promote the recovery of vegetation.As a comparison, grazing land had significant lower plant species, coverage, biological diversity and community evenness than which in the region with engineering measures. Furthermore, fencing enclosure for afforestation promoted significantly better than sandy enclosure in the short term.(5) Soil fertility and soil moisture content were main limiting factors for the vegetation growth in the process of vegetation restoration of desertified land in Xiaobazi.Soil organic matter, soil available nutrients and soil moisture which showed a greater factor loading were the dominant factors for vegetation restoration in this region.(6) The formation and development of soil crusts was related to its media types, slope aspect and litter coverage. Soil crusts changed the soil mechanical composition and the chemical composition of the sandy surface and the soil under it. It also reduced rainwater infiltration to the soil and deep soil moisture decreased, but the powerful retention ability of soil crusts made surface soil moisture increased significantly. Thus, the soil temperature under soli crusts decreased which made the evapotranspiration of it much less than the bare sand.(7) Vegetation can effectively reduce wind speed and reduce wind erosion.The average temperatures were large difference and which in bare sand was the highest among different underlying surface. The average temperature of different vegetation was also different. The vegetation had a significant role to reduce the air temperature.The sequence that different vegetation reducing the temperature was:artificial forest>natural bush forest>artificial grassland>natural grassland. Ground surface temperature was closely related to land surface type and vegetation coverage. Vegetation has an obvious function in regulating soil temperature. The regulatory function of soil temperature in natural bush forest was greater than which in the artificial forest, artificial grassland and artificial grassland. Water is the major limiting factor for plant survival and growth in arid and semi arid areas. Soil moisture was significantly related to vegetation water consumption. The soil moisture in forest land was lower than which in other types of vegetation land and the soil moisture in grazing land was always keeping the highest value.
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