Preliminary exploration of native grassland classification of Gansu Province based on GIS and comprehensive and sequential grassland classification method

Based on improved spatial interpolation method, DEM data was used as cofactor. when the correlativity between the cofactor and the spatial data was relatively high, the precision of interpolation could be increased effectively. For the annual accumulated temperature data, the correlation coefficient between DEM elevation and the annual accumulated temperature was 0.769, and the relativity was high, so the precision of interpolation can be increased effectively with DEM elevation. The ME of four interpolation methods in turn are: IDWSplineOKCK, comparing with the Ordinary Kriging method, the interpolation precision of Cokriging method had a significant increasing from 1.861 to 1.169, a 35% raising, hence used the CK method to generate the annual accumulated temperature spatial database. For the annual average precipitation data, the correlation coefficient between DEM elevation and the annual average precipitation was 0.372, relativity was low, and the precision of interpolation can not be increased effectively with DEM elevation. The ME of four interpolation methods in turn are: IDWSplineCKOK, the OK method had highest interpolation precision, accordingly used the OK method to create the annual average rainfall spatial database. Based on the interpolation results and the standards of integrated classification system, with the map overlay analysis function of GIS software, the moisture index (K) spatial database and the distribution map of grassland types of Gansu province were regenerated. From this map, it can be seen that there are totally 18 grassland types in Gansu province, bestriding 5 heat levels from cold to warm and hot, 6 humidity grades levels from extreme arid to humid. Formed several vegetation cover types which are forest, foreststeppe, typical steppe, desertsteppe, semidesert and desert from southeast to northwest of Gansu, and alpine, subalpine, meadow, mountainous forest and meadow steppe from hilltop to foot of mountain. The disciplines of genesis and distribution of native grassland of Gansu province was reflected basically, and useful basic theory was provided for continuous study.