Limited impact of fire and grazing on methane emission in a tropical inundated savanna

Atmospheric methane concentrations experience an ongoing increase following a brief stabilization in the early 2000s. Evidence suggests that recent increases are driven by different mechanisms than during the pre-2000 period, with enhanced natural emissions from tropical regions as a leading hypothesis. However, the processes responsible for increasing methane emissions from tropical wetlands remain poorly understood. Improving our understanding of the magnitude, variability, and drivers of methane emissions from tropical wetlands is therefore essential. As large parts of these systems are subject to some form of land management, an often-overlooked factor is how such management practices might influence methane emissions. Land management practices such as prescribed burning and cattle grazing can strongly affect biomass accumulation and, consequently, the availability of carbon substrates for methanogenesis. We therefore hypothesized that treatments leading to a reduced biomass accumulation would also result in lower methane emissions. Here, we present results from a field experiment designed to assess the effects of cattle grazing and prescribed burning on the structure and functioning of an inundated savanna in the Orinoco Plains, Colombia. We conducted chamber measurements of CO₂ and CH₄ fluxes under four treatments: no fire and no grazing, fire and no grazing, no fire and grazing, and fire and grazing. In total, 571 chamber measurements were collected between January 2024 and October 2025. We found that the inundated tropical savanna acted as a substantial source of methane during the wet season (mean 27 mg CH4 m⁻² d^-1) and as a small sink during the dry season (mean -1.5 mg CH4 m⁻² d^-1). Although treatments significantly altered biomass accumulation (range 128–685 g m⁻²), differences in methane emissions among treatments were not significant, indicating that grazing and prescribed burning do not exert a strong control on methane emissions in this tropical wetland ecosystem.