Abstract: Afforestation for carbon sequestration is an effective strategy to combat global warming. Pinus sylvestris var. mongolica is one of the widely-used afforestation tree species in the semiarid region of northern China. It covers the vast semiarid area from eastern Inner Mongolia to the Loess Plateau. The assessment and prediction of carbon storage of P. sylvestris var. mongolica forests is helpful to understanding the effect of afforestation on carbon sink in semiarid regions of China. Seven allometric growth equations developed for environmental settings in  semiarid Inner Mongolia were collected. Then the vegetation carbon storage of P. sylvestris var. mongolica forests in 2022 was evaluated by combining the surveyed tree height, diameter at breast height and age of single trees. The  biomass and carbon storage of P. sylvestris var. mongolica forests in 2030, 2040, 2050 and 2060 were predicted. The results showed that height and diameter at breast height of P. sylvestris var. mongolica increased with an overall growth trend of “slow-fast-slow”, and the maximum values were predicted to reach at 18 and 16 years old, respectively. The trend of biomass of P. sylvestris var. mongolica forest was similar to that of diameter at breast height and tree height. The carbon storage of P. sylvestris var. mongolica forests in this area tended to be stable at the age of 20 years old. Carbon density of P. sylvestris var. mongolica forests was 0.23-0.87 kg·m^-2 in 2022, and will be 1.2-3.4 kg·m^-2 in 2030, with an average of 2.0 kg·m^-2. In 2040, carbon density of P. sylvestris var. mongolica forests will be 1.3-3.7 kg·m^-2, with an annual increment of 0.2-0.3 kg·m^-2 in ten years. In 2050, carbon density of forests will be 1.4-3.7 kg·m^-2, with an annual growth rate of 0.08%-0.4%. In 2060, carbon density of P. sylvestris var. mongolica forests will still be 1.4-3.7 kg·m^-2. However, there is a substantial difference in carbon storage calculated based on the seven allometric growth equations, indicating great uncertainty in estimation of forest carbon stock and the critical needs of multi-equation comparison.

Key words: carbon stock, Pinus sylvestris var. mongolica, allometric growth equation, semiarid planted forest