Profiles of carbon stocks in forest, reforestation and agricultural land, Northern Thailand

A study was conducted to assess carbon stocks in various forms and land-use types and reliably estimate the impact of land use on C stocks in the Nam Yao sub-watershed (19°05′10″N, 100°37′02″E), Thailand. The carbon stocks of aboveground, soil organic and fine root within primary forest, reforestation and agricultural land were estimated through field data collection. Results revealed that the amount of total carbon stock of forests (357.62 ± 28.51 Mg·ha⁻¹, simplified expression of Mg (carbon)·ha⁻¹) was significantly greater (P < 0.05) than the reforestation (195.25 ± 14.38 Mg·ha⁻¹) and the agricultural land (103.10 ± 18.24 Mg·ha⁻¹). Soil organic carbon in the forests (196.24 ± 22.81 Mg·ha⁻¹) was also significantly greater (P< 0.05) than the reforestation (146.83 ± 7.22 Mg·ha⁻¹) and the agricultural land (95.09 ± 14.18 Mg·ha⁻¹). The differences in carbon stocks across land-use types are the primary consequence of variations in the vegetation biomass and the soil organic matter. Fine root carbon was a small fraction of carbon stocks in all land-use types. Most of the soil organic carbon and fine root carbon content was found in the upper 40-cm layer and decreased with soil depth. The aboveground carbon:soil organic carbon: fine root carbon ratios (ABGC: SOC: FRC), was 5:8:1, 2:8:1, and 3:50:1 for the forest, reforestation and agricultural land, respectively. These results indicate that a relatively large proportion of the C loss is due to forest conversion to agricultural land. However, the C can be effectively recaptured through reforestation where high levels of C are stored in biomass as carbon sinks, facilitating carbon dioxide mitigation.