Abstract
A significant impact of fires is the transfer to the atmosphere of the elements contained in combusted biomass. This study was carried out in the Guinean savanna of Lamto (Côte d’Ivoire) to evaluate fire-mediated carbon and nutrient losses from biomass according to the date of burning. The fire regimes tested consisted of three different burning dates: early (EF), mid (MF), and late (LF) season fires, on nine 0.5 ha plots. Carbon and five elemental nutrients were assessed in the aboveground biomass prior to burning and in ash and unburnt biomass after fires; losses were assessed by subtraction. The proportion of nutrients transferred to the atmosphere varied from 42 % (K) to 98 % (C). The lowest losses were recorded during the EF and the greatest during the MF and LF. Emission of CO2 was relatively greatest during the EF than during the MF and LF (16, 14 and 13 t ha-1 respectively). The proportion of the fine ash fraction (< 1 mm) was the greatest during MF. The highest concentrations of K, P, Ca and Mg occurred in this fraction, most susceptible to losses due to wind and rainfall. The percentage losses of C, N and K were positively correlated with fire maximal temperatureand flame height, explaining the relatively higher losses during MF. Over the long term, the MF applied annually, would lead to important depletion of soil nutrients, particularly N and P, which contributes to the low availability of nutrients in the soils of Lamto savannas.
Highlights
Biomass burning is recognized as a significant source of greenhouse gases, which significantly impacts global atmospheric chemistry and climate change (Reid et al, 2005; Tunved et al, 2006)
Fresh fuel load before burning, residual unburnt fuel, and total ash load were higher during early fire than mid-season and late fires
3.2 Ash Fractions During the early fire, the proportion and quantity of the fine ash fraction was the greatest and the coarse ash fraction proportion the lowest, and there was no difference between the quantity of medium and coarse ash fractions
Summary
Biomass burning is recognized as a significant source of greenhouse gases, which significantly impacts global atmospheric chemistry and climate change (Reid et al, 2005; Tunved et al, 2006). A great fraction of these emissions is released by the burning of savannas, followed by forests and croplands (Andreae, 1991; NASA, 2005). Accurate estimates of CO2 emissions from biomass burning at local and regional levels are urgently needed to refine global estimations and better understand the impact of fire on climate. Fires in African savannas are an essential factor of the global CO2 balance. Numerous studies view the West African savanna as one of the important “burn centers” of the planet (Menaut, 1993; Liousse et al, 2004; NASA, 2005). Our study aims at making up for the scarcity (Helas et al, 1995) of quantitative assessments of CO2, carbon and nutrients emissions from savanna fires in West Africa
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