Afforestation programs have huge potential to store carbon, thereby contributing to mitigate climate change. However, the voluntary acceptance by landowners crucially depends on their economic outcome. We (i) assess the carbon sequestration potential of afforestation projects in various Chinese regions by comparing different tree species, project durations and regional particularities, (ii) analyze the costs and benefits of tree species used for timber and fruit production as well as bamboo, and (iii) compare them with alternative crops under different climatic and economic conditions. Finally, we calculate the minimum compensation required by farmers to convert cropland to forests assuming a joint production of timber or fruits and carbon sequestration. No compensation is needed when cropland with relatively low revenues is to be converted. In contrast, compensation payments must be high for converting land used for cash crops, such as sugarcane. For fruit trees, the amount of carbon sequestered is low, but selling fruits and nuts is quite profitable. Consequently, in most cases there is no compensation needed. The minimum price per carbon credit decreases with increasing project duration because more carbon is stored per hectare, and in consequence, the required payments per credit are lower. This does not hold for fast-growing trees like eucalyptus and poplar, for which the minimum price increases with extended project duration. Bamboo shows a high carbon sequestration potential, and becomes economically more attractive by including carbon revenues. Carbon credits can often compensate the opportunity costs of alternative land uses, except for afforestation on highly productive cropland. We demonstrate that the economic attractiveness of afforestation projects is strongly context dependent and varies substantially across regions. The findings can contribute to the cost-efficient design of carbon sequestration projects. The methodology can be applied to other regions in the developing world.

Soil organic carbon (SOC) is the largest component of the terrestrial biosphere carbon pool. Afforestation is an effective solution to mitigate Carbon (C) emission and sequester C into soils. However, how and to which extent afforestation influences SOC stock changes are not well understood. This study conducts a quantitative review that synthesizes 544 data points from 261 sites from 90 papers, to examine the impact of afforestation on SOC changes in three soil layers (0-20 cm, 20-40 cm and 40-60 cm). 212 data points are obtained by standardization and/or extrapolationwith high reliability. The results indicate that stand age has significant effects on the SOC stock dynamics under different conditions of previous land use types, plant functional types, temperature or precipitation. The effect is greatest at the topsoil layer of 0-20 cm. Previous land use types significantly influence SOC accumulations, but these effects are not significant in the first 10 years or after 30 years of afforestation. Besides, afforestation on grassland seems to sequester more SOC than that of cropland in the long term. Plant functional types also significantly affect SOC dynamics, with deciduous hardwood reporting a continuous increase of SOC contents at soil depth of 0-60 cm during the whole afforestation period. On the other hand, the accumulation of SOC in evergreen hardwood and evergreen softwood start from the third decades. Higher SOC accumulation rates are observed under evergreen hardwood but no significant differences were found between deciduous hardwood and evergreen softwood for the longer period after afforestation (>20 years). Mean annual temperature and precipitation negatively affect SOC accumulation in the first two decades of afforestation, however, the effects become positive in the later years.We also found that initial SOC stocks did not play a major role in SOC sequestration. In other words, lower SOC soils could also sequestrate a significant amount of SOC after reforestation.