Carbon stocks and carbon sequestration potentials in ecosystems of two afforestation species in low hills of northern Yanshan Mountains

Afforestation projects play an important role in ecosystem restoration and will contribute to global carbon cycles. In this paper, two major afforestation species Populus simonii andPrunus sibiric in low hills of northern Yanshan Mountains were studied with natural grassland as a control, and the effects of conversion from grazing land into forest on the ecosystem carbon stocks and carbon cycles were analyzed. The results show that after conversion from grazing lands into forests, the carbon stocks in vegetation and litter generally increased as the conversion duration prolonged. Without human disturbance, the carbon stocks in 9-, 15-, 18-, 22-, and 29-year-old Populus simonii forests were 7147.45, 7461.67, 7509.90, 8468.38, and 8247.85 g•m-2, respectively; the carbon stocks in 9-, 15-, 18-, 22-, and 26-year-old Prunus sibirica forests were 6695.44, 6700.82, 8011.86, 8001.92, and 7981.92 g•m-2, respectively. Under the disturbance of intermediate logging, the ecosystem carbon stock in 36-year-old Populus simonii forest was 7702.58 g•m-2. Soil carbon stock first decreased and then increased as the conversion duration prolonged. The ecosystem carbon stock sequestration potentials in 22-year-old Populus simonii and 18-year-old Prunus sibirica forests were 2078.01 and 1621.55 g•m-2 respectively, indicating that after conversion from grazing land into forest, the ecosystems in the study area are a considerable carbon sink in the long run.