Analysis and evaluation of cultivated land decrease in eastern part of Qinghai Plateau

Abstract: Western development and a series of ecological environmental regulation projects have been carried out in West China since 1999. In order to solve the contradictions among economic construction, ecological environment construction, and the protection of cultivated land, it is important to understand and master where and the reason why cultivated land changed. Taking Haidong, which is located in the eastern part of Qinghai Plateau, as the study area, this paper applied a comprehensive remote sensing classification method which is based on the geographical division of land use to classify the 1999 and 2009 remote sensing data. The areas of cultivated land that changed and remained were extracted respectively from the results of their classification in 1999 and 2009 to analyze the main direction and spatial distribution of the cultivated land conversion. Then combined with the terrain data, as well as economic and social development data, this paper analyzed the main factors that affected cultivated land conversion quantitatively by a Logistic method. The results showed that from 1999 to 2009, the area of cultivated land in the eastern agricultural area of the Qinghai Plateau decreased by 1393.25 km2, and 1811.78 km2 of cultivated land converted to constructive land and forests/grass. This includes 157.05 km2 of cultivated land that converted to land for construction, which was mainly distributed in cultivated land with a gradient below 2°and altitude below 2600m, and 1695.73 km2 of cultivated land with steep and high altitudes between 2600m and 3200m returned to forests or pasture. That 78.82% of the cultivated land with a gradient over 25°returned cultivated land to forests or grass, indicates that projects of returning farmland to forests or grass have resulted in the noticeable achievements in Eastern agricultural region of the Qinghai Plateau. The result of cultivated land change indicated that the decrease of cultivated land can be divided into two parts: one is occupied by constructive land, and the other is the ecological conversion of the arable land. Therefore, we can turn the problem of why cultivated land decreased into the problem of which factors are the main ones that affect the expansion of land for construction and returning farmland to forests respectively. Given the availability of data, the related factors in this article included altitude, slope, aspect, distance to stream, distance to river or lake, distance to straightway, distance to highway, distance to administrative station, and population density. Logistic is a good tool to analyze these factors. The analysis of these factors showed that the contribution of altitude is -66.46% for the expansion of land for construction, namely a higher altitude equaling less land for construction. The contribution of the slope for returning farmland to forest (grassland) is as high as 91.25%, which indicates that the land conversion project in eastern part of Qinghai Plateau was effectively implemented according to policy. Finally, this paper reached the conclusion that the occupation of land for construction purposes and ecological restoration from farmlands are working in a rational and powerful manner in the eastern agricultural area of the Qinghai Plateau. This study helped to reconcile the conflicts among ecological construction, economic development, and the protection of cultivated land, and provides the basis for further sustainable development of the regional economy.