The magnitude and persistence of soil NO, N₂O, CH₄, and CO₂fluxes from burned tropical savanna in Brazil

Abstract

Among all global ecosystems, tropical savannas are the most severely and extensively affected by anthropogenic burning. Frequency of fire in cerrado, a type of tropical savanna covering 25% of Brazil, is 2 to 4 years. In 1992 we measured soil fluxes of NO, N 2 O, CH 4 , and CO 2 from cerrado sites that had been burned within the previous 2 days, 30 days, 1 year, and from a control site last burned in 1976. NO and N 2 O fluxes responded dramatically to fire with the highest fluxes observed from newly burned soils after addition of water. Emissions of N‐trace gases after burning were of similar magnitude to estimated emissions during combustion. NO fluxes immediately after burning are among the highest observed for any ecosystem studied to date. These rates declined with time after burning and had returned to control levels 1 year after the burn. An assessment of our data suggested that tropical savanna, burned or unburned, is a major source of NO to the troposphere. Cerrado appeared to be a minor source of N 2 O and a sink for atmospheric CH 4 . Burning also elevated CO 2 fluxes, which remained detectably elevated 1 year later.