Natural and human disturbances have non-linear effects on whole-ecosystem carbon persistence in an African savanna (Preprint) Whole-ecosystem carbon persistence

Disturbance-mediated shifts in carbon persistence – the inverse likelihood of experiencing severe losses due to disturbances – within terrestrial ecosystems remain poorly understood despite their critical role in global carbon dynamics. Moreover, huge uncertainties in estimating carbon storage in disturbance-prone dryland ecosystems renders the assessment of their contribution to the global carbon budget difficult. This study investigated the effects of land-use change on carbon storage in an African savanna landscape, focusing on agricultural intensification and wildlife conservation as major land-use change pathways that alter disturbance regimes. We adapted conventional tree inventory and soil sampling methods to suit dryland ecosystems, enabling robust quantification of carbon storage for aboveground and belowground carbon in woody vegetation (AGC and BGC, respectively), and soil organic carbon (SOC) across land-use pathways and two vegetation types (savannas and woodlands). For assessing the effects of environmental drivers on AGC, and whole-ecosystem carbon (Ctotal), Generalized Additive Mixed Models were used. Results indicate different carbon persistence across carbon reservoirs, vegetation types and along land-use change pathways. Shrub AGC always was the least persistent carbon reservoir in savannas. Compared to shrub AGC in low-disturbance sites, it decreased on average by 56% along the conservation pathway and by 90% along the intensification pathway. Tree AGC was the least persistent reservoir along the intensification pathway in woodlands, with decreases of 95%. Elevated SOC stocks, particularly along the intensification pathway, suggest preferential use of naturally carbon-richer soils for agriculture. Strong unimodal impacts of disturbance agents, notably large herbivores and woodcutting, on AGC and Ctotal indicate that intermediate disturbance levels benefit carbon storage. Our findings suggest complex, interactive effects of natural and human disturbances on the carbon persistence of ecosystem compartments and whole-ecosystem carbon, and highlight the substantial role of locally adapted disturbance regimes for carbon sequestration, offering insights crucial for carbon certification programmes in drylands.