Soil Organic Matter Dynamics in the Ericaceous and Afroalpine Belts of the Bale Mountains, Ethiopia: Influence of Vegetation, Fire, and Topographic Factors

Soil organic matter (SOM) dynamics in highaltitude tropical ecosystems are poorly understood, yet critical for predicting carbon-climate feedbacks. We characterized SOM pools in the Bale Mountains National Park (Ethiopia) across vegetation types (Ericaceous belt, fragmented Ericaceous belt, Afroalpine heathland, giant Lobelia area), fire histories (recently burned, 10–25 years post-fire, unburned >25 years), and topographic positions. Using physical fractionation, we separated coarse (149–2000 μm) and fine (53–149 μm) particulate organic matter (POM) and mineral-associated organic matter (MAOM, < 53 μm). Particulate organic matter dominated the SOM pool (>99%), with C representing only 0.05–0.07% of total organic carbon. The Ericaceous belt had the highest coarse POM (11.38 g kg⁻¹), while the fragmented Ericaceous belt showed the lowest (8.96 g kg⁻¹, p = 0.042). Intermediate fire disturbance (10–25 years) increased coarse and fine POM by ~12–13% compared to recently burned or long-unburned sites. Topographic position significantly influenced POM fractions, with northern slopes accumulating the highest amounts (p <  0.05). Cation exchange capacity was strongly positively correlated with POM fractions (r = 0.86, p <  0.001), while elevation showed a negative relationship (r = –0.38, p = 0.04). The extremely low proportion of MAOM suggests limited long-term stabilization capacity, making these soils vulnerable to warming-induced decomposition. Our results demonstrate that fire history, vegetation, and topography interact to control SOM dynamics, and that conservation strategies should prioritize minimizing anthropogenic disturbance to preserve SOM inputs and ecosystem resilience.