Effects of the implementation of ecological restoration policies on soil organic carbon storage in a discontinuous soil region.

摘要

Estimating soil organic carbon (SOC) storage for soils with discontinuous distribution in the karst regions of southwest China poses a challenge due to the predominant carbonate bedrock. In addition, it is not clear how effective the ecological restoration and reconstruction policies, which have been conducted in this region since the 1990s, have been in terms of SOC sequestration. In this study, we explored the ability of an empirical model and validated it using field survey data to predict the coverage of discontinuous distribution soil in a karst region in southwest China. Employing the soil coverage map, survey data of SOC at a soil depth of 0-15 cm, and three land use/cover maps in 1990, 2004, and 2011, we estimated the changes of SOC storages in the study area. Results showed that the land use/cover changes induced by the implementation of ecological restoration policies promoted SOC storage in the karst region. The SOC storage increased from 2.34 Tg to 3.01 Tg and soil organic carbon density increased from 2.72 kg/m2 to 3.50 kg/m2 over the study period. The mountain closure policy, Grain for Green program, and migration program currently implemented in the karst region have contributed to a decline in the rate of SOC decomposition and the reduction of soil disturbance, which resulted in carbon sequestration in the global carbon cycle while also improving the ecologically fragile karst environment. SOC storage may have been overestimated by almost twofold while ignoring the discontinuous distribution features of soil cover in the karst region. However, along with an increase in both population and agricultural activities, SOC storage in the nonkarst area declined from 1990 to 2011. With the ecological restoration occurring in the karst area, losses of SOC induced by increased farming activities in the nonkarst area should not be ignored.