Decoupled recovery of soil and vegetation carbon reveals mineral-driven stabilisation in reforested tropical montane ecosystems

Reforestation is increasingly promoted as a nature based climate solution, yet the degree to which soil carbon recovers alongside vegetation remains uncertain, particularly in deeply weathered tropical soils. While rapid gains in above ground biomass are often interpreted as indicators of ecosystem recovery, it is unclear whether such gains translate into meaningful changes in below ground carbon pools.

We investigated soil and vegetation carbon dynamics across a thirty year gradient of forest disturbance and recovery in tropical montane forests of Kibale National Park, Uganda, spanning primary forest, passive natural regeneration, and actively replanted stands. The study integrates depth resolved soil organic carbon stocks to one metre, stable carbon isotope profiles, soil physical and geochemical properties, and long term forest inventory data from permanent monitoring plots. By combining carbon stocks, isotopic indicators, and soil mineral properties, we assess how strongly soil carbon is coupled to forest recovery and at what depths soils respond to changes in vegetation. The analysis reveals clear contrasts between above ground and below ground carbon trajectories and highlights the role of soil depth and legacy effects in shaping carbon storage in recovering tropical forests.

Our results provide new insight into the limits of using biomass recovery as a proxy for soil carbon sequestration and underline the importance of depth resolved and process oriented approaches when evaluating reforestation outcomes.