5 CONCLUSION
In the south-eastern sandy land in Horqin in northern China, enclosing grasslands within a shelter belt of Populus × beijingensis(FG) or raising in them Pinus sylvestris var. mongolica orUlmus pumila in widely distributed but small pockets increased the accumulation of C in the ecosystem (in plants and in soil) significantly. Mainly because of the differences in the tree species, the C pool was the largest in FG. Biomass C in all the three treatments was also significantly higher than that in the control. The greatest increase in soil C was in the upper layer of the soil profile (to a depth of 50 cm). All the three approaches will contribute greatly to C sequestration globally and are suitable for arresting desertification in semi-arid areas that may be lacking in adequate levels of soil moisture and available nutrients.