Land use/cover pattern survey under the background of “Grain for Green” policy implementation in the loess hilly-gully region, China——A Case Study of Majiagou catchment, Ansai County, Shaanxi Province

摘要

Land use change to some extent results from the change of land policy and human environmental consciousne ss,lt will lead to profound influence on regional environment as well as a global change.The Loess Plateau is the most serious area of soil erosion in the world.it has a friable environment. The irrational land use and low forest cover is the fundamental reason. The land use converting from farmland to forest/grass with the implementation of the "Grain for green" policy in 1999 is an important measure to improve the ecological environment in the Loess Plateau. The percentage of forest/grass cover and its pattern changes the processes of surface flow and sediment discharge, so influences the hydrological regime. What it like of the current land use/cover pattern in the region is poor known. The paper took the catchment of Majiagou in Ansai County, the typical loess hilly-gully region as a research field to check the land use/cover situation after 10 years implementation of the policy. The land use data in 2008 were obtained from the combination work of 2007's remote sensing imagine interpretation and field survey in December, 2008. based on the land use map in 1990 provided by the land use bureau of Ansai county. The results showed that the area of the main land use types: farmland. forest and grassland, accounted for 91.6% of the catchment. The grassland was most extensive with 56.77% of the total area of catchment. and then followed by forest and farmland. the area percentage were 19.60% and 15.25%, respectively. During the field survey, while lots of the slope farmland was detected to convert to grass cover. still a number of slope farmland stand there. Among the current farmland, terrace land, slope farmland and other flat land along the river bed occupies 44.8%, 42.4% and 12.9%, respectively. The catchment was divided to upper, middle and lower reaches based on the hydrological system. The concentricity of each land use types varies in each reaches of catchment. The situation of each land use types in the upper reaches is similar with that of total catchment. The farmland, including orchard. mainly concentrates in the middle reaches due to the gentle landform development. While the forest in the catchment singularly focus in the lower reaches because of the property of land subject to the Ansai town, which services its ecological function for the whole Ansai town as a park like.