Seasonality of carbon emissions from biomass burning in a Zambian savanna

Seasonal trends in carbon emissions from savanna fires in Western Province, Zambia, were investigated in the early dry season (early June to early August) 1996. The objective was to determine the effect of fuel moisture content on combustion factors and modified combustion efficiency (the ratio of the molar concentration of CO₂ released to the molar concentration of CO and CO₂). Early dry season biomass burning may emit fewer emission products of complete combustion (CO₂) and more products of incomplete combustion (e.g., CO). Thirteen experimental sites were burned between June and August 1996, six in a miombo woodland and seven in a dambo grassland. Fires were lit in each ecosystem as the fuels dried so as to monitor changes in fire behavior as the dry season progressed. Total fuel loading ranged from 1884 kg ha^-1 to 3314 kg ha^-1 in the dambo and 8953 kg ha^-1 to 13233 kg ha^-1 in the miombo. Moisture content of green grass decreased from 127% to 69% in the dambo and from 119% to 33% in the miombo through the length of the study. Combustion factors (CF, the percentage of fuel consumed) increased from 44% to 98% in the dambo. CF values for the miombo increased from 1% to 47%. Fire line intensity increased from 288 kW m^-1 to 5271 kW m^-1 in the dambo and from 25 kW m^-1 to 5274 kW m^-1 in the miombo. Results indicate that combustion factors and combustion efficiency values follow seasonal trends correlating to metrics of vegetation moisture content, which may alter the type and quantity of carbon emissions. Incorporation of seasonal dynamics of the fire regime should be included in global estimates of carbon flux in the subtropics and in the amount of products of incomplete combustion per unit area burned.