Abstract: Decision on gradually reforesting and regrassing some of the dry land based on ARCGIS in Sichuan Province is discussed here,which is very important for the ecological restoration and sustainable development in Sichuan.Five steps are included.Firstly,the database platforms for making decisions are established including land use,soil erosion,DEM,slope,eco-environmental quality,normalization vegetation index(NDVI),precipitation,temperature,vegetation subregion,soil type,administrative district,waterbody buffer and residential area buffer which are created by using ARCGIS.All data are referenced to the same projection and coordination,and interpolated as grid data with a resolution of 100 m.Secondly,the dry land from landuse database is overlain with slope database,soil erosion database,NDVI database,eco-environmental quality database,waterbody buffer data and residential buffer data.Thirdly,the expert knowledge about reforesting and regrassing some of the dry land is collected,and the models for finding a suitable place for being returned back to forestland and grassland are formulated based on ARCGIS by using the knowledge.There are 724495 and 333085 ha of dry land to be gradually converted into forestland and grassland on the basis of the models,which respectively account for 9.3% and 4.3% of the dry land.Fourthly,the suitable place is overlain with precipitation layer and temperature layer to find out the place respectively suitable for trees and grass by the model that is formulated by using the knowledge of forest distribution and ARCGIS.In the first order,there are 702362 and 22133 ha to be respectively converted into forestland and grassland,or 96.9% and 3.1% of the suitable place for firstly being returned back to forestland and grassland.In the second order,there are 331357 and 1728 ha to be respectively converted into forestland and grassland,which respectively account for 99.5% and 0.5% of the suitable place for secondly being returned back to forestland and grassland.Finally,the distributions of the place suitable for trees and the place suitable for grass in administrative district,vegetation subregion and soil type region were obtained by using the overlay and spatial statistic analysis,which are of benefit to the selection of suitable tree and grass species for reforesting and regrassing.The research shows that with this the method considerable manpower,material and financial resources can be used sparingly.The result can not only be presented in table form,but also in graphic form,which is very useful for planning,executing,and managing the program of reforesting and regrassing some of the dry land in Sichuan province.

Key words: geographic information system, reforesting and regrassing some of the dry land, spatial overlay analysis, decision model