The final analysis is based on 45 studies published between 2015 and 2025, from 18 sub-Saharan African countries, whose most represented hubs are: Cameroon (28%), Nigeria (12%), Ghana (9%), South Africa (9%), Ethiopia (8%), and Kenya (6%). The publications come mainly from international indexed journals (Geoderma, CATENA, SOIL, Nature Communications, Land Degradation & Development), confirming a high level of methodological quality. The language distribution places English at 82% and French at 18%, consistent with the English-language dominance of African environmental journals.

The results converge towards a dominant influence of three factors, namely annual precipitation, average temperature, and soil texture and mineralogy (Table 1). The analysis of the corpus shows that soil organic carbon (SOC) variability in sub-Saharan Africa is mainly controlled by three factors: rainfall, temperature, and mineralogy. Rainfall gradients explain 30% to 55% of the spatial distribution of the SOC. In semi-arid areas receiving 400 - 900 mm/year, stocks fall by 0.25% - 0.80%, while sub-humid areas (1000 - 1500 mm/year) maintain higher levels. Regions with high interannual variability, such as the Sahel and the Sudanian savanna, have the most unstable stocks. Temperature also has a marked negative influence. Data from 19 studies indicate an average loss of 0.21% ± 0.07% of SOC per additional degree Celsius, reflecting an acceleration of mineralization processes. This thermal sensitivity is accentuated in sandy-silty and ferralsols soils, which are less capable of retaining organic matter over the long term. Mineralogy is an essential determinant: soils rich in iron oxides (ferralsols, oxisols) stabilize carbon better via organo-mineral bonds, unlike the sandy soils of the Sahel and southwestern Nigeria, which lose their carbon more quickly under climatic stress. These results confirm that the resilience of the SOC is closely dependent on climate-soil interactions.

Table 1. Influence of pedoclimatic parameters (annual precipitation, temperature, and soil texture and mineralogy) on SOC variations in tropical soils in SSA.

The analysis of the 71 selected studies shows that 87.3% of the studies identify climate mechanisms as the main determinants of soil organic carbon (SOC) dynamics in sub-Saharan Africa. Three blocks of processes dominate the entire corpus.

Modification ofCarbon Input Fluxes(69% ofStudies)

Variations in rainfall, seasonality, and aridity directly modify the input of plant biomass. Our synthesis shows:

Average reduction in organic inputs of −18% to −45% in areas with decreasing rainfall.In systems receiving < 900 mm/year, studies report a decrease in SOC of 0.25% to 0.80%.Sub-humid areas (1000 - 1500 mm/year) maintain more stable levels, with variability < 25%.

The consequence is the low availability of biomass, less litter, and consequently less embodied carbon.

AcceleratedDecompositionandMineralization(74.6% ofStudies)

Temperature and fluid alternations are the most cited factors:

Mean SOC loss in the range of 0.21% ± 0.07% per +1˚C, observed in 19% of quantitative studies.In 52% of the studies, the increase in temperature leads to a 15% - 35% acceleration of microbial metabolism.Drought followed by rain: peaks of mineralization increase losses by 8% to 22% in sandy soils.

These thermogenic processes alternate between dry and wet to ensure the accelerated release of CO₂.

Instability orEnhancementofOrgano-Mineral Stabilization(62% ofStudies)

The texture and mineralogy strongly modulate the sensitivity of the SOC to climatic stress. Soils rich in iron oxides and clays show increased carbon stabilization, estimated at between 20% and 45%, thanks to a high organo-mineral retention capacity. Conversely, sandy or poorly aggregated soils suffer rapid losses, reaching (−30%) to (−55%) under prolonged heat or water stress. In 41% of the studies, extreme events cause aggregates to disintegrate, reducing the physical protection of carbon. Mechanically, the climate therefore acts on the mineral structure, altering the soil’s ability to store carbon sustainably.

The spatial distribution of the SOC in SSA reveals an extremely contrasting ecological gradient ranging from very rich reservoirs to ultra-deficient areas (Table 2). Rainforests remain the main sinks, regularly exceeding 60 - 90 t∙C∙ha⁻¹, thanks to the combination of high biomass, moisture, and deep clay soils. The volcanic highlands also show significant stocks (30 - 50 t∙C∙ha⁻¹), supported by favorable mineralogy. In contrast, the Sudano-Guinean Savanna drops to 15 - 30 t∙C∙ha⁻¹, marking a first break linked to the seasonality of humidity and agricultural pressures. The Sahel is the most critical area, rarely above 10 - 15 t∙C∙ha⁻¹, with extreme vulnerability due to aridity, low clay content, and accelerated degradation. Anthropogenic systems are profoundly modifying this landscape. Agroforestry systematically improves stocks (+18% to +33%), while ecological restoration allows partial but slow recovery (40% to 70%). This contrast confirms that the SOC is simultaneously dependent on climate, mineralogy, and management practices, drawing a mosaic of vulnerabilities and sequestration potentials.

The effect of climate change interacts strongly with anthropogenic dynamics. Three major transformations are emerging. Deforestation and forest conversion appear to be the most destructive pressures. The 31 studies identified reveal that the conversion of rainforests to agriculture causes a significant reduction in SOC, estimated at between 15% and 45% in Central African ecosystems. In Cameroon’s forest areas, where conversion to cocoa plantations and timber exploitation are particularly intense, losses reach 30% to 65%. These decreases are explained by the elimination of vegetation cover, the decrease in litter inputs, the increase in erosion, and the disruption of the microclimate stabilizing the carbon accumulation processes (Table 3).

Table 2.Spatial synthesis of soil organic carbon (SOC) stock in tropical soils across SSA.

Table 3.Impact of land use practices on SOC stocks.

Conventional agriculture and intensification aggravate these losses, especially in areas densely cultivated on ferralsols. Repeated ploughing weakens soil aggregates, accelerates mineralization, and exposes surface horizons to water erosion. Studies indicate a loss ranging from 0.3 to 1.2 t∙C∙ha⁻¹∙year⁻¹, reflecting a rapid decrease in SOC. The soils of the Plaine du Noun, which are highly degraded, now have critical levels (<1%), testifying to a collapse of essential soil functions.

In contrast, conservation practices, agroforestry, and long-fallow land demonstrate a high potential for SOC restoration and stabilization. The gains are substantial, with an increase of 18 to 33% in organic stocks on the surface. Agroforestry practices, especially those associated with cocoa cultivation under shade, also promote increased stabilization of deep carbon between 30 and 60 cm, strengthening the biogeochemical resilience of the soil.

Overall, these results confirm that anthropogenic dynamics can amplify or mitigate the effects of climate change. The ability of tropical soils to sustainably store carbon, therefore, depends directly on the management systems adopted, highlighting the importance of a transition to sustainable agricultural and forestry practices.

Sustainable management practices are the most effective levers for restoring or increasing soil organic carbon (SOC) stocks in tropical environments in sub-Saharan Africa. No-till systems, combined with rotations and permanent plant cover, induce gains of 9% to 20% of SOC. These benefits are higher in clay-rich soils (>30%), due to the increased ability of clay minerals to stabilize organic matter, as well as in sub-humid areas where plant productivity supports organic inputs (Table 4).

Table 4.Land use transformations and impacts on soil organic carbon (SOC).

The application of biochar and organic amendments is a second major lever. Acidic ferralsols from Cameroon, Ethiopia, and Tanzania show increased stability due to organo-mineral interactions promoted by iron oxides. Agroforestry systems are distinguished by their ability to improve both surface and deep-horizon carbon. The increases are significant: 0.4 to 1.1 t∙C∙ha⁻¹∙year⁻¹ at the surface and 0.2 to 0.6 t∙C∙ha⁻¹∙year⁻¹ at 30 - 60 cm. The presence of trees improves soil structure, root biomass diversity, and micro-conditions favorable to carbon accumulation. Forest and pasture restoration programs demonstrate a high recovery capacity: 40% to 70% of the initial SOC is restored after 15 to 20 years. This underscores the resilience of tropical ecosystems when anthropogenic pressures decrease.

Almost all studies assessing the spatial variability of SOC in tropical areas closely associate organic storage with rainfall levels ([36]; [30]; [39]). The corpus shows that 30 to 55% of the regional variability of the SOC is explained by the precipitation gradient. In semi-arid areas where rainfall is less than 900 mm/year, the water deficit sharply reduces plant biomass, limiting litter inputs and increasing the frequency of fires, which accelerates surface carbon loss ([5]). Conversely, sub-humid areas, receiving more than 1200 mm/year, show higher stocks, due to more sustained plant productivity, humidity favorable to aggregate formation, and a moderate microclimate ([16]; [31]). However, the effect of precipitation is not linear: above a certain threshold, excess moisture induces an acceleration of mineralization or leaching losses, especially in highly weathered ferralsols soils ([46]; [10]). Thus, the SOC responds in a non-monotonic way to rainfall variations, according to a water optimum specific to soil-vegetation combinations.

The mechanisms linking temperature and SOC are clearly emerging: a 1˚C increase leads to an average loss of 0.21% ± 0.07% of SOC in tropical areas ([49]; [1]). Thermal augmentation intensifies heterotrophic respiration, stimulates microbial decomposition, and accelerates the disorganization of organo-mineral complexes ([17]; [22]). The work of [38] indicates that soils dominated by unprotected organic matter, such as Sahelian sands, are particularly vulnerable to temperature increases. Conversely, soils rich in 1:1 clays and iron oxides show higher inertia, as carbon is associated with stable mineral structures ([40]; [35]). This increased thermal sensitivity explains the extreme vulnerability of the Sahelian savannah, where the combination of heat + water deficit induces a double stress. Studies by [15] demonstrate that the increased frequency of heat waves weakens the stability of aggregates, reducing the soil’s ability to encapsulate carbon.

Forty-two studies in the corpus emphasize the central role of mineralogical properties in carbon stabilization. Ferralsols soils, which are very common in Central Africa, contain high amounts of iron and aluminum oxides, conferring a significant ability to retain organic compounds via adsorption and co-precipitation ([20]; [35]). These soils show carbon stabilization rates 20% to 45% higher than sandy soils under identical climatic conditions. In contrast, sandy soils in the Sahel or southwestern Nigeria lose 30% to 55% of their SOC under prolonged climatic stress, due to their low aggregation capacity and a mineralogy low in protective fine particles ([30]; [24]; [25]). In 41% of the studies, extreme episodes (intense rainfall, severe droughts) induce rapid disintegration of the aggregates, exposing organic matter to accelerated mineralization ([48]; [9]). It thus appears that mineral properties determine the degree of amplification or mitigation of climate impacts.

Changes in land use accentuate climate effects. More than 30 studies confirm that forest conversion drastically reduces SOC stocks, with losses ranging from 15 to 45% in rainforests and up to 65% in Cameroonian areas converted to cocoa plantations ([18]; [26]). The loss of forest cover reduces litter inputs, disrupts the microclimate, and exposes surface horizons to erosion. Conventional agricultural systems based on frequent ploughing show the highest losses: 0.3 to 1.2 t∙C∙ha⁻¹∙year⁻¹, especially on ferralsols where the fragile structure does not tolerate mechanical disturbance ([28]; [45]). The soils of the Plaine du Noun are a good example of these processes, with critical SOC levels often <1% ([29]; [23]).

Work on conservation agriculture shows robust gains, between 9 and 20%, particularly on clay soils in subhumid areas ([24]; [27]). According to the work of [17] and [12], biochar appears to be one of the most effective long-term interventions with increases of 12% to 60%. The effects are most pronounced in acidic soils where microbial activity is moderate. Agroforestry also strengthens SOC stocks with gains of 0.4 to 1.1 t∙C∙ha⁻¹∙year⁻¹ at surface and 0.2 to 0.6 t∙C∙ha⁻¹∙year⁻¹ at depth ([4]; [31]; [3]). Restored forest systems show a remarkable ability to recover 40% - 70% of lost carbon in 15 - 20 years ([16]; [34]).

High-resolution mapping reveals a strong regional heterogeneity. Dense moist forests often exceed 60 t∙C∙ha⁻¹, while Sahelian savannahs show values below 15 t∙C∙ha⁻¹ ([8]). Cameroon illustrates an exceptional gradient: <10 t∙C∙ha⁻¹ in the northern Sahelian against 80 t∙C∙ha⁻¹ in the western mountains ([44]; [45]; [23]). Machine learning-based models achieve accuracies of 62% - 78%, confirming the importance of spectral data and climate variables ([6]).