The potential for carbon sequestration by afforestation can be limited in dryland river basins under the pressure of high human activity

Abstract

Dryland regions cover >40 % of the Earth's land surface. Both human activities and climate change have driven forest expansion in parts of dryland regions. Afforestation has been implemented widely to enhance carbon sequestration and benefit the ecological environment of many global drylands. However, the potential and available afforestation space in drylands is uncertain due to the conflicts between additional forest areas and available water. How afforestation will affect the potential for forest carbon stock is also unclear. This paper assessed the future spatial distribution of afforestation and potential forest carbon stock in a typical dryland region, the Yellow River Basin (YRB), which has experienced rapid afforestation and high human activity pressure over the past several decades. Combining the future land use change model (FLUS) and local important development planning, we simulated future afforestation distributions and estimated potential forest carbon stock under the ecological restoration, urban expansion, and cultivated land protection scenarios. The afforestation carbon stock was predicted by considering the dynamic change trends of the mature forest, the immature forest, and new afforestation. The results demonstrated that the potential afforestation area would be limited to 4000 km² in the YRB accounting for less than one-twentieth of the total forest area. Accordingly, the maximum potential forest carbon stock would increase only 59.5 × 10⁶ t. These findings implies that afforestation programs in drylands should further consider the optimum allocation of afforestation space and the balance between carbon and water in drylands, especially under a changing climate with increasing human activities.

Keywords: Afforestation; Drylands; Potential carbon stock; Scenario-based modeling; Yellow River Basin.