Analysis of land use /cover change for recent 20 years in Majiagou catchment in the Loess Plateau, China

摘要

Irrational land use in the Loess Plateau results in the severe soil erosion. This paper takes Majiagou catchment in Ansai county, the first national land use survey map in 1990 was got from the Bureau of Land use Survery of Ansai County. The 2008 land use map was obtained based on the method of field survey. With ARCGIS tool, two land use maps were overlaid and the dynamic changes were analyzed. The results showed that. from 1990 to 2008. farm land and grassland had a decreasing trend with 11.88% and 1.58% of the area of the catchment. At the same time. forest. orchard and residential land had got the a increasing trend by 11.61%、1.73% and 0.01% of the catchment area. The ratio of the area of farm land, forestry and grassland was changed from 3 : 1 :6 to 2:2:6 in the catchment. The main transferring direction among the land use system were from grassland to forest (6.73km2), farm land to grassland (6.43km2), farm land to forest (1.75km2), farm land to orchard(1.23km2). The land use types with high transferring speed from 1990 to 2008 were forest land. orchard and farm land, they were 8.06%、2.41%、 -2.43%, respectively. Although the area of forest land increases over past 20 years, the landscape still hold the feature of artificial ecosystem with the nature of instability and non-sustainability. Land use change was derived from the national policy of "Grain for Green" and the changing of farmers' operating procedure.