Land Use/Cover Changes And Its Driving Force Research In Last 30 Years In Changwu County

Changwu County, located in Weibei Plateau area, is a typical region for dryland agriculture, also the most eroded area in the Loess Plateau. In terms of land use/ coverage, the county has changed remarkably in the latest 30 years under the guidance of state policies, becoming a national demonstration county of Grain for Green, but also experiencing the conversion from grain base to grain-fruit base of Shaanxi Province. Therefore, Changwu County is selected as a case study in this article and an analysis is made of land use types, change in farmland quantity and quality and its spatial distribution to determine its driving factors, which is aimed to provide scientific supports for the sustainable development of economy and food security of the county. The main conclusions obtained are as follow:(1) In 2009, Farmland, orchard, forest land and grassland are the main patterns of land use in the county. Forest land, the most widely distributed type, took up an area of 179.99 km~2, accounting for 31.74%, followed by farmland, orchard, grassland and residential land, occupying 159.62 km~2 (28.15%), 83.57 km~2 (14.74%), 76.20 km~2 (13.44%), 49.76 km~2 (8.77%) respectively. While waterbody accounted for only 3.04% and unused land 0.13%.(2) The dynamic analysis of land use change of the county in 1983-1993 and 1993-2009 shows that farmland declined continuously throughout the two periods, by 71.64 km~2, 58.23 km~2 respectively, while orchard, compared to the initial 18.26 km~2 in 1983, increased by 1.7 times in 1993 and 3.6 times in 2009. Forest land rised by 36.85 km~2 and 28.15 km~2 respectively at the end of each period, and grassland by 28.33 km~2. We can also see that residential land did not significantly change, waterbody decreased somewhat, and unused land decreased at a considerable rate over the 30 years. The trend of the landscape pattern is characterized by: the increase in degree of patch fragmentation, in shape index, and in the patch fractal dimension after decrease.(3) The quantity and topographic distribution of farmland in 1983-1993 and 1993-2009 show that farmland on the plateau and on the slope of gully declined continuously, while that on the valley experienced a rise in area. In 1983-1993 and 1993-2009, farmland on the plateau decreased by 17.02 km~2 and 23.46 km~2 respectively, mainly converting to orchard and residential land; one on the slope of gully decreased by 56.59 km~2 and 36.36 km~2 respectively, mainly transforming to orchard, forest land, grassland and residential land; and the other on the valley rose up by 1.98 km~2 and 1.28 km~2 respectively, converting largely from grassland in the former period and from waterbody in the latter one.(4) With a preliminary analysis of the socio-economic statistics combained, the driving force for farmland use change in Changwu County are concluded as the development of socio-economy, the advancement of agricultural modernization and the implemetation of national Grain for Green policy.