Contrasting fire effects on SOC storage under Ferralitic and Ferruginous soils in Madagascar

Increasing the soil organic carbon (SOC) stocks as prone by the 4‰ initiative could be challenged by frequent natural fires. Fires in forests and open grassy ecosystems remove above and belowground biomass and can strongly alter SOC dynamics. Knowledge about this alteration remains unclear across different environments. This study examined how environmental factors regulate fire impacts on SOC. SOC stocks were assessed in 307 plots at 0–10 cm, 0–30 cm, and 0–100 cm depths across two contrasting bioclimatic regions of Madagascar—the dry northwest and the subhumid southeast. The sampling design integrates multiple drivers, including land cover, climate, soil type, and topography, along with fire frequency, ranging from unburned to annually burned areas.
Fire frequency alone does not explain SOC patterns at 0–100 cm depth, unlike in surface layers. Significant interactions with topographic position and slope aspect influence SOC stocks, indicating that fire effects are not restricted to shallow horizons but extend into deeper soil layers. Forests and shrublands are prone to SOC decline with more frequent fire. In contrast, grasslands display highly variable SOC responses to fire. This challenges the assumption that frequent burning always depletes carbon and instead indicates that fire effects are strongly modulated by site-specific conditions. For reforestation sites, SOC patterns are driven by the stand age and species composition, rather than fire–environment interactions. Understanding these interactions can help better target carbon sequestration efforts and support sustainable land management in Madagascar’s fire-prone ecosystems.