Carbon sink-source dynamics across ecuadorian coastal tropical dry forests: unraveling the seasonal balance of soil carbon inputs and CO2 efflux

Abstract

Tropical dry forests play a crucial role in climate change mitigation by sequestering atmospheric carbon, yet the balance between soil carbon storage and soil CO 2 emissions remains poorly understood across contrasting forest subtypes. This study evaluated the seasonal carbon sink–source dynamics of three representative Ecuadorian coastal tropical dry forests by quantifying soil organic carbon (SOC), soil CO 2 efflux, and net carbon sink capacity (NCSC), while identifying the main edaphic drivers regulating these processes. Field measurements were conducted during the rainy and dry seasons in 12 permanent plots distributed across a Lowland Semideciduous Forest (LSF), a Deciduous Pacific Forest (DPF), and a Lowland Deciduous Forest and Shrubland (LDF). Soil organic carbon stocks, soil CO 2 efflux, soil physical and chemical properties, and vegetation diversity were quantified using standardized laboratory and field protocols. Annual SOC storage reached 11,439.96 Mg C yr −¹ in LSF, 327,111.22 Mg C yr −¹ in DPF, and 281,744.18 Mg C yr −¹ in LDF, whereas annual soil CO 2 emissions were substantially lower, totaling 1,876.46 Mg C yr⁻¹ in LSF, 80,353.00 Mg C yr −¹ in DPF, and 43,526.52 Mg C yr −¹ in LDF. Consequently, all three forest subtypes exhibited a positive Net Carbon Sink Capacity, confirming their role as net carbon sinks despite marked seasonal variability. Mean NCSC across the rainy and dry seasons was highest in LSF (56.6 Mg C ha −¹ ), followed by LDF (49.4 Mg C ha −¹ ) and DPF (47.0 Mg C ha −¹ ).These findings provide new evidence that Ecuadorian tropical dry forests maintain a positive carbon balance across contrasting climatic conditions and emphasize the importance of subtype-specific conservation and restoration strategies to maximize long-term carbon sequestration under climate change.