Fire impact on C and N losses and charcoal production in a scrub oak ecosystem
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Fire profoundly modifies the terrestrial C cycle of about 40% of the Earth’s land surface. The immediate effect of fire is that of a net loss of C as CO2 gas and soot particles to the atmosphere. Nevertheless, a proportion of the ecosystem biomass is converted into charcoal, which contains highly recalcitrant molecular structures that contribute to long-term C storage. The present study aimed to assess simultaneously losses to the atmosphere and charcoal production rates of C and N compounds as a result of prescription fire in a Florida scrub-oak ecosystem. Pre-fire and post-fire charred and unburned organic matter stocks were determined for vegetation leaves and stems, litter and soil in 20 sub-plots installed in a 30-ha area that was subjected to prescribed fire. Concentrations of C and N were determined, and fluxes among pools and to the atmosphere were derived from these measurements. Soil C and N stocks were unchanged by the fire. Post-fire standing dead biomass contained 30% and 12% of pre-fire vegetation C and N stocks, respectively. In litter, post-fire stocks contained 64% and 83% of pre-fire C and N stocks, respectively. Most of the difference in relative losses between vegetation and litter could be attributed to substantial litter fall of charred and unburned leaves during the fire event. Indeed, an estimated 21% of pre-fire vegetation leaf C was found in the post-fire litter, while the remaining 79% was lost to the atmosphere. About 3/4 of the fire-induced leaf litter fall was in the form of unburned tissue and the remainder was charcoal, which amounted to 5% of pre-fire leaf C stocks. Charcoal production ranged between 4% and 6% of the fire-affected biomass, i.e. the sum of charcoal production and atmospheric losses. This value is below the range of literature values for the transformation of plant tissue into stable soil organic matter through humification processes, which suggests that fire generates a smaller quantity of stable organic C than humification processes over decades and potentially centuries.
KeywordsCarbon cycle Charcoal Fire CO2 flux Scrub oak
This work was supported by a grant from the Smithsonian Environmental Research Center. The Institut National des Sciences de l’Univers department of the Centre National de la Recherche Scientifique is acknowledged for financial support under the framework of the program ‘Dynamique et stabilisation des matières organiques dans les sols tropicaux: influence des brûlis, de l’érosion et de la mise en culture’. We would like to thank the teams of Florida CO 2 site and Dynamac Corporation for fieldwork, and Naoise Nunan, Tammy Foster and John Erickson for reviews. Three anonymous reviewers also helped to improve this manuscript.
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