Carbon dynamics and soil greenhouse fluxes in a Florida's native rangeland before and after fire

Abstract Grazing lands, including the native rangelands, cover an extensive area of the southeastern United States, representing an important component of the carbon balance for the region. In Florida, native rangelands extend over 3.1 Mha, experiencing a natural fire frequency between 2 – 5 years and a strong climatic variability. Management includes prescribed fire and mechanical brush control. This study is the first of its kind assessing the impacts of prescribed fire and climatic variability on C dynamics and warming potential in Florida's rangeland. We used a combination of eddy covariance and chamber measurements to estimate net ecosystem C exchange (NEE), greenhouse gas (GHG, CO2, CH4, and N2O) emissions, and C in pre and post-fire aboveground biomass. NEE measurements extended four and a half years since 2016, included a fire event during the fourth year (May 1st, 2019), and two and a half years of GHG measurements . Pre-fire net ecosystem production (NEP) was -368 ± 41 g C m−2 yr−1 and decreased to -181 g C m−2 yr−1 during fire year. After accounting for fire C emissions, net ecosystem C balance was -43 g C m−2 yr−1 in 2019. Soil CO2 dominated GHG emissions increasing 172 g C m−2 yr−1 after fire, N2O fluxes increased from 29, pre-fire year, to 41 g m−2 yr−1 (CO2eqv) post-fire, the ecosystem was a CH4 sink between -1.7 and -3.9 g m−2 yr−1 CO2eqv. The fire effect on C uptake was short-lived, the ecosystem recovered fast after fire, NEP reached pre-fire monthly average two months after, increases in warming potential caused by fire were offset within the next year after. The Florida's rangeland is a suitable ecosystem to mitigate global warming, it acted as a strong C sink offsetting -1148 g C m−2 in four years including a drought and a fire year.