Soil organic carbon stocks under different forest types in Pokhare khola sub-watershed: a case study from Dhading district of Nepal

Abstract

Assessment of carbon stock in vegetation and soil is an essential step in estimating the carbon sequestration potential of an ecosystem. This study was carried out to quantify total carbon sequestration in different forest types of the Pokhare Khola sub-watershed (forested area of 312 ha), Dhading, Nepal. The inventory for estimating the above and belowground biomass of different forests was carried out using the stratified random sampling method with 0.5% sampling intensity for plant biomass. The dry biomass was calculated using allometric models.Four soil profiles from each forest types were excavated and soil samples were taken from the soil profile up to 1 m depth at intervals of 20 cm. The soil bulk density was collected using a core ring sampler of 9.5 cm long and 4.2 cm diameter and organic carbon content was assessed using the Walkley and Black method. The total soil carbon stock in all forest types was estimated at 42,523 t/ha, Shorea forest 62%, Schima-Castonopsis forest 25%, Pine-Shorea forest 5.5%, and degraded forest 7.5%. The distribution pattern of carbon stock was mainly due to the biomass of the stand, carbon content of soil and area coverage of these forest types. The total biomass carbon in forest was found as 77.68 t/ha and SOC sequestration 58.6 t/ha.The study showed that soil organic carbon was higher in the upper layer (0-20cm) in all forest types and rapidly declined below the 20-40cm depth. The rate of SOC concentration is in decline trend as the depth increased. The study revealed that a Shorea forest and Schima-Castonopsis forest are better than a Pine-Shorea forest and degraded forest in carbon stocking.

Variation in Soil Organic Carbon under Different Forest Types in Shivapuri Nagarjun National Park, Nepal

“…In almost all cases, SOC concentration has been found higher at the upper level of soil. Pradhan et al [22] reported greater SOC concentration in the Schima-Castanopsis forest than in other forest types, but this study shows that the SOC concentration is found higher in the oak forest as the forest was dense and due to different microbial activities in the soil. e greater the depth, the lower the SOC concentration for all types of forest.…”

“…Due to lower SOM content, less aggregation, fewer roots and other soil dwelling organisms, and soil compaction, the BD of soil will increase with increasing soil depth. Pradhan et al [ 22 ] reported that the organic matter content of soil decreases with increasing soil depth and that this results in a decrease in soil porosity and also in soil compaction. With the increase in depth in each forest type, a gradual increase in bulk density was seen.…”

Soil organic carbon estimation along an altitudinal gradient of chir pine forests in the Garhwal Himalaya, India: A field inventory to remote sensing approach

“…High BD in the soil layer between 30 and 60 cm could be due to the presence of thick layer of rock or gravel, which subsequently decreased with the soil depth. The increase in BD with increasing depth is attributed to the concentration of organic matter in the soil profile (Handayani et al, 2012), which corresponds to decrease in organic matter with depth, leading to decrease the soil porosity and soil compaction (Pradhan et al, 2012) and mixing with mineral material in the profile (Schulp et al, 2008).…”

The effect of exclosures on restoration of soil properties in Ethiopian lowland conditions

“…where WBC (%) = Walkley-Black carbon content of the fine fraction (< 2 mm), D = soil depth (cm), BD = soil bulk density (g cm −3 ); CF = % of volume of coarse fragments. The volumetric content of the coarse fragments (> 2 mm material) was calculated from a density of rock fragments value of 2.65 g cm −3 [55].…”