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 Aug ust) 1996. The objective was to determine the effect of fuel moisture conte nt on combustion factors and modified combustion efficiency (the ratio of t he 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 i n each ecosystem as the fuels dried so as to monitor changes in fire behavi or 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 stud y. 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 da mbo and from 25 kW m(-1) to 5274 kW m(-1) in the miombo. Results indicate t hat combustion factors and combustion efficiency values follow seasonal tre nds correlating to metrics of vegetation moisture content, which may alter the type and quantity of carbon emissions. Incorporation of seasonal dynami cs 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 p er unit area burned.