文章在分析延安生态建设示范区2000—2003年间各土地利用类型的数量变化和空间特征的基础上,引入退耕指数、退耕影响系数等指标研究退耕还林草对示范区土地利用结构变化的影响。结果显示,示范区已退耕坡耕地36.07%,平均每年退耕12.02%,全区的退耕影响系数高达4.76,该结果表明大规模的退耕还林草活动对区域土地利用变化的影响很大,它推动了土地利用结构的优化。分乡镇的研究显示,退耕对示范区各乡镇土地利用变化的影响存在一定的差异,除2个乡镇的退耕影响系数远远低于全区平均水平外,其他7个乡镇都高于全区平均水平。

By converting slope farmland into forestland and grassland,it is possible to increase the effective cover area of forest and grass vegetion,mitigate soil erosion,and improve agricultural environments.Beside vegetation has the ability of protecting environment and changing the natu,ral environment on which soil erosion happened thoroughly,converting slope farmland into forestland and grassland also promote local tarmers to change their traditional way of farming.And improve per unit area output of grain by regulating structure of land use.Based on the ana,lysis of the quantitative changes of various land use types and spatial characteristics in Yan'an Ecological Construction Demonstration Area(ECDA)from₂000 to 2003 by RS,GIS and statistical methods,this paper studies the influence of slope farmland conversion into forestland and grassland on the structure of land use in Yanan ECDA through introducing the de,farming index,the de,farming influence coefficient and others.At the end of 2003,36.07% of steep slope farmland have been converted into forestland and grassland,averaging about 12.02% of conversion annually.The de,farming influence coefficient of Yan'an ECDA is 4.76,that is to say,4.7% of other kinds of land have been converted into other usage,which is a scientific and planned adjustment guided macroscopically by government,leading eco,environment and rural economy to develop healthily and smoothly in benign circulation.The result shows that large,scale slope farmland conversion into forestland and grassland affects greatly the change of regional land use because it promoted optimizing the structure of land use.Studies on towns and tounships indicated that the impact of de,farming on land use change of various towns is different.Except the de,farming influence coefficients of two towns much lower than the average level of the demonstration area,those of the other seven towns are higher than the average level of the demonstration area,The de,farming influence coefficient is relative to natural conditions and the level of land,use of each town respectively.