Soil Organic Carbon Along an Elevational Gradient in the Eastern Region of the Democratic Republic of the Congo

Abstract

Tropical montane forests (TMF) can store large amounts of soil organic carbon (SOC), because of slower decomposition rates at high elevations. However, our understanding of the factors affecting SOC in montane forests in Africa is still limited. Understanding SOC is critical for estimating carbon losses from deforestation and forest degradation, as well as potential carbon finance mechanisms. Focused on the understudied montane forests of eastern Democratic Republic of the Congo (DRC), we investigated: if SOC increased with increasing elevation; if changes in SOC were related to soil pH or nutrient availability, and if high SOC compensated for low aboveground carbons stocks at high elevations. Soil samples were taken at 0-30cm of depth in 30 1-ha plots established along an elevation gradient covering four forest types: submontane, lower, middle and upper montane and two soil types.SOC ranged from 58.2 ± 8.6 Mg C ha -1 to132.8 ± 30.8 Mg C ha -1 in lower and upper montane, respectively. SOC stocks increased predictably with increasing elevation, and soil chemical characteristics (mainly soil acidity, N and decreasing K+) helped to explain the differences in SOC between forest types. SOC was significantly greater (98.6 ± 31.66 Mg C ha-1) in Andisol than in Ferralsols (65.87 ± 15.79 Mg C ha -1 ). Our estimates were within the range of SOC values reported elsewhere in TMF in Africa, but different methodologies are often used, which makes comparisons challenging. We highlighted that large amounts of SOC are found in the montane forests of eastern DRC, which should be considered when studying the effects of deforestation and forest degradation. We also call for a standardized approach to SOC quantification in montane forests in Africa, so that we are able to understand this important carbon pool in the biosphere.

Keywords: montane forest, SOC increase, elevation, forest type, soil properties, Aboveground carbon