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Ensuring ecological security in the environmental degradation has always been a top priority in China. Under the Grain for Green Program (GGP), millions of hectares of farmland in the karst region of Guizhou province have been converted into Zanthoxylum bungeanum plantations in order to arrest and reverse "rocky desertification". The aim of this study was to estimate biomass increment and carbon accumulation in four different aged (1-, 4-, 7- and 10-year-old) Z. bungeanum stands, as well as the distribution of carbon stock among the various biomass components and soil depths. The total plant biomass measured for the four stands of different ages was 0.05, 6.76, 12.22, and 16.71 Mg ha(-1), respectively. Compared with other plant species in the region, Z. bungeanum plantations has a larger capacity for accumulating biomass. The C content in components of Z. bungeanum tree ranged from 40.47% to 48.64% with the mean value of 44.67%. The use of the standard coefficient (50%) in converting biomass into C storage results in 10% overestimation. Soil organic carbon (SOC) storage at the top soil (0-30 cm) increased from 75.22 Mg C ha(-1) in 1-year-old stand to 80.06 Mg C ha(-1) in 10-year-old stand, and decreased with increasing soil depth for each stand age. Total ecosystem C storage increased with plantation age, averaging 75.24, 79.79, 84.43, and 87.62 Mg C ha(-1), respectively, of which more than 90% was stored in the soil. Our study suggests that the protection of SOC in surface soils during plantation management practices plays a crucial role in improving the C sequestration. Data of plantation area and annual biomass C accumulation rate (under the GGP in Guizhou province) indicate a net C sink of 6.35 x 10(6) Mg in 2010, corresponding to a 4.92% compensation of C emission from energy consumption in that year. Besides increasing C storage over time, the large-scale planting of Z bungeanum has the potential of restoring severely degraded soils in the karst region of SW China. (C) 2015 Elsevier B.V. All rights reserved.