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In forest ecosystems, soil organic matter facilitates carbon sequestration and serves as a sink for atmospheric CO2. Carbon in forest soils plays an important role in mitigating global climate change. Soil carbon density was measured at three depths (0-20, 20-40, and 40-60 cm) in four different elevation classes sites at the forest exterior and forest interior in the sub-tropical forests of southeastern China. Results showed that soil organic carbon (SOC) varied between 46.48 and 83.12 Mg ha(-1) at forest exterior and 50.18 and 90.68 Mg ha(-1) at forest interior in different elevation classes. A significant increasing trend in soil organic carbon was found with an increase in elevation at both forest exterior and forest interior. Similarly, a positive correlation between soil organic carbon and elevation was observed at forest exterior (R-2 = 0.87, P = 0.0001) and forest interior (R-2 = 0.93, P = 0.0001). The percentages of soil carbon at 0-20, 20-40, and 40-60 cm depths at forest exterior and forest interior were 47.24-52.76, 47.23-52.77, and 46.95-53.05% respectively. Soil bulk density was directly related to soil depth and inversely related to elevation at forest exterior and forest interior. Overall the mean SOC at forest exterior and forest interior was 60.83 Mg ha(-1) and 68.20 Mg ha(-1) respectively. The study showed that there is a 5.7% difference in soil carbon density between forest exterior and forest interior which highlights the fact that ignoring edge effects may lead to overestimation of soil carbon density. Therefore, we suggest the establishment of permanent sample plots sites at the forest exterior and forest interior and recommend regular periodic surveys of soil for accurate forest soil carbon measurement.