Estimation of soil organic carbon stocks: A case study of forest soils in the green zone of Bogd Khan mountain

Abstract

This study examined soils in the 25 -hectare forest area of the green belt in the Ar and Uvur Zaisan valleys of Bogd Khan Mountain. Soil profiles were sampled, morphological descriptions were conducted, and agrochemical properties were determined, including the content and stocks of soil organic carbon (SOC). The forest soils of the study area are classified as mountain mollic umbrisols. In urban green spaces, intensive human activities—such as high population density, increased vehicular and machinery traffic, and inappropriate land use planning—have led to soil and surface layer degradation, compaction, and erosion, as well as a reduction in plant species diversity, resulting in accelerated land degradation. Therefore, we urgently require effective measures to protect the green belt forests and implement optimal land-use management. The aim of this study was to determine SOC content and stocks in the green belt forests of Bogd Khan Mountain, specifically in the Ar and Uvur Zaisan valleys of Ulaanbaatar. To achieve this, we assessed soil fertility indicators and estimated SOC stocks within the study plots. Results from the Uvur Zaisan valley showed that soils in the 0–30 cm layer were moderately acidic (pH 5.20–5.80), with humus content of 8.1–14.1%, SOC of 4.7–8.2%, cation exchange capacity of 10.50–70.00 mg, phosphorus content of 0.77–1.49 mg, and potassium content of 32.00–60.00 mg. In comparison, soils from the Ar Zaisan valley were slightly acidic (pH 6.08–6.70), with humus content of 7.0–12.5%, SOC of 4.0–7.2%, cation exchange capacity of 11.0–60.7 mg, phosphorus content of 0.77–1.00 mg, and potassium content of 37.50–81.00 mg. SOC stock assessments revealed 148.67 t ha⁻¹ in the 0–30 cm soil layer of Uvur Zaisan forests and 137.29 t ha⁻¹ in Ar Zaisan forests.