Data: Anthropogenic Disturbances Superimpose Climate Effects on Soil Organic Carbon in Savanna Woodlands of sub-Saharan Africa

Savanna ecosystems in sub-Saharan Africa (SSA) harbor substantial yet relatively unexplored reserves of soil organic carbon (SOC). Our study aimed to unravel the intricate interplay between climate, reference soil groups (RSGs), and anthropogenic disturbances in shaping SOC dynamics in these ecosystems. We analysed SOC along climosequences across natural savanna woodlands in Mozambique and Zambia, with varying mean annual temperature (MAT; 20 - 24°C) and mean annual precipitation (MAP; 365 - 1227 mm). Anthropogenic disturbances were assessed through comprehensive field surveys and remote sensing of tree cover and vegetation indices changes from 1980 to 2019. There was no discernible effect of MAT. Yet, bulk SOC and all SOC pools increased with increasing MAP, which explained, however, only 30% of the data variability. This weak relation was caused by anthropogenic disturbance, which tended to raise SOC stocks in the dry savanna but resulted in significant SOC losses at > 600 mm MAP. For sites with little, if any, disturbance in the past decades, we found significant RSG-specific effects of MAP on SOC, explaining up to 85% of data variability. Consequently, the precipitation regime is central in controlling SOC stocks in SSA native savanna woodlands. However, human presence changed the C balance with an estimated release of 1.5 Gt of CO2-C in 20 years; another 1.4 Gt CO2-C potentially could be lost with increasing population spread into these otherwise pristine environments. Accurate modelling of climate-change effects on the C cycle must include the transformative impacts of current human activities, such as wood harvesting and grazing.