Abstract:

The well-researched analysis of land use change and carbon storage in the northern farming-pastoral ecotone such a fragile ecological environment， under the background of returning farmland to forest （grass）， could help generate a scientific basis for local regional ecological construction and sustainable development. Based on the land use data of the three periods of 2000-2018 in this area， the quantity， rate and spatial pattern characteristics of land use change in the past two decades were investigated through land transfer matrix， landscape index， and meanwhile carbon storage also got estimated quantitatively by InVEST model. The final results indicated that： （1） The land use types mainly consisted of grassland， cultivated land and forest land in the northern farming-pastoral ecotone， covering an area of more than 4.30×10⁵ km² and accounting for 91.83% of the total area. Among them， forest land and construction land expanded significantly， and meanwhile grassland and cultivated land declined remarkably because the area of their mutual circulation was the largest， as high as 1.67×10⁴ km². The landscape pattern of the study area generally converged to "concentration-dispersion". （2） In the past two decades， the total carbon storage floated at 5.14-5.28 billion^{ton in the northern farming-pastoral ecotone， with a carbon increment of three million tons benefited from the policy of returning farmland to forest （grass）. Besides， the carbon density reached nearly 110 t·hm-2. In conclusion， the change of land use grew increasingly vigorous in the northern farming-pastoral ecotone and the policy of returning farmland to forest （grass） not only had made some progress but also significantly improved the carbon sequestration function towards this area.}

Key words: returning farmland to forest （grass）, northern farming-pastoral zone, land use, landscape index, InVEST model, carbon storage