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

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Savanna ecosystems in sub-Saharan Africa (SSA) harbor substantial yet relatively unexplored reserves of soil organic carbon (SOC). Our study unravels for the first time the interplay between climate, reference soil groups (RSGs), and anthropogenic disturbances in shaping SOC dynamics in these ecosystems. We analyzed SOC along climosequences in natural woodlands in Mozambique and Zambia, with mean annual temperature (MAT; 20-24°C) and precipitation (MAP; 365-1227 mm). Anthropogenic disturbances were assessed through comprehensive field surveys and remote sensing of vegetation and indices changes. MAT and evapotranspiration (PET) had no discernible effect on SOC. Bulk SOC, particulate organic matter (POM), and mineral-associated organic matter (MAOM) stocks in the topsoil (0-10 cm) increased with MAP, though this relationship was not significant for subsoil. MAP explained only 35% of topsoil SOC variability, limited by anthropogenic disturbances, which raised SOC stocks in the dry savanna but resulted in SOC losses at > 600 mm MAP, and extended into subsoil. For sites with little disturbance, in the past decades, there were RSG-specific effects of MAP on SOC, explaining up to 85% of data variability. In disturbed sites, human presence altered the C balance to an extent that, as a rough estimate, could account for up to 2.6 Gt CO2-C loss over 20 years in wetter sites, with another 2.4 Gt CO2-C at risk as populations spread into these otherwise pristine environments. Accurate modelling of climate-change effects on the C cycle must, therefore, include the transformative impacts of current human activities, such as wood harvesting and grazing