Soil Organic Carbon Stocks of the Kitonga Catchment Forest Reserve, Tanzania: Variation with Elevation

Abstract

The carbon stored in forest soils has significant implications in global climate change processes. Few studies on soil organic carbon (SOC) have been reported from the Miombo woodlands. This study was conducted to assess SOC at different elevations in selected sites of the Miombo woodlands of the Kitonga Catchment Forest Reserve (KFR). Ten sampling points located at different elevations were selected and georeferenced. At each point, three randomly selected mini-soil pits were excavated for the collection of soil samples. The soil samples from different soil depths, up to 60 cm, were collected and composited from the mini-pits in three replicates. The SOC was analyzed using the wet oxidation method. The mean SOC stock increased from 15.2 to 26.7 Mg ha⁻¹ at 928 and 1,548 masl, respectively, for the Fluvisols, and from 11.3 to 44.9 Mg ha⁻¹ at 1,258 and 1,598 masl, respectively, in Cambisols. Conversely, SOC stocks decreased with elevation in Leptosols, and the trends were 28.9–12.5 Mg ha⁻¹ at 831 and 1,083 masl, respectively. The mean topsoil (0–15 cm) SOC stock was 26.3 ± 5.0 Mg ha⁻¹ in Fluvisols, 20.6 ± 7.0 Mg ha⁻¹ in Leptosols, and 19.4 ± 7.0 Mg ha⁻¹ in Cambisols. The SOC stocks in the 15–30 cm soil depth decreased by 57 %, 41 %, and 31 % compared to those of the top soils (0–15 cm) in Leptosols, Fluvisols, and Cambisols, respectively. The relatively higher amount of SOC stocks in the surface horizons justifies the need for conservation of the intact vegetation of the Miombo woodlands in the KFR.