No abstract

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 CO 2 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 postfire 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 fireaffected 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.

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Fires occur naturally in many wetlands and are widely used for marsh management. We examined the responses to fire ofJuncus roemerianus and Spartina bakeri marshes on Kennedy Space Center, Florida. In each marsh, we determined vegetation cover before burning on 5 permanent 15 m transects in the greater than 0.5 m and less than 0.5 m layers and sampled biomass on 25 plots (0.25 m2). One year after burning, we repeated the sampling.Species composition one year after burning was similar to that before the fire in both Juncus and Spartina marshes. Minor species tended to increase, but this was significant only in the less than 0.5 m layer. In mixed stands, f'tre appeared to favor Spartina bakeri. Total cover (sum of the cover values for each species) in both marshes reestablished by one year after burning. Biomass did not recover as rapidly. In the Juncus marsh one year after burning, live biomass was 47.2%, standing dead 18.7%, and total biomass 29.3% of that before burning.In the Spartina marsh, biomass one year after burning was live 42.3%, standing dead 21.4%, and total 30.7% of that before burning. Fire increased the ratio of live to dead biomass from 0.82 before burning to 1.85 one year ",ffter the fire in theJuncus marsh. In the Spartina marsh, the ratio of tire to dead biomass increased from 0.80 before burning to 1.59 one year after burning.

No abstract