Biomass fire consumption and carbon release rates of rainforest-clearing experiments conducted in northern Mato Grosso, Brazil

Biomass consumption and carbon release rates during the process of forest c learing by fire in five test plots are presented and discussed. The experim ents were conducted at the Caiabi Farm, near the town of Alta Floresta, sta te of Mato Grosso, Brazil, in five square plots of 1 ha each, designated A, B, C, D, and E, with different locations and timing of fire. Plot A was lo cated in the interface with a pasture, with three edges bordering on the fo rest, and was cut and burned in 1997. Plots B,C, D, and E were located insi de the forest. Plot B was cut and burned in 1997. Plot C was inside a defor ested 9-ha area, which was cut and burned in 1998. Plot D was inside a defo rested 4-ha area, which was cut in 1998 and burned in 1999. Plot E was insi de a deforested 4-ha area, which was cut and burned in 1999. Biomass consum ption was 22.7%, 19.5%, 47.5%, 61.5%, and 41.8%, for A, B, C, D, and E, res pectively. The effects of an extended curing period and of increasing the d eforested area surrounding the plots could be clearly observed. The consump tion, for areas cut and burned during the same year, tended toward a value of nearly 50% when presented as a function of the total area burned. The ab oveground biomass of the test site and the amount of carbon before the fire were 496 Mg ha(-1) and 138 Mg ha(-1), respectively. Considering that the b iomass that remains unburned keeps about the same average carbon content of fresh biomass, which is supported by the fact that the unburned material c onsists mainly of large logs, and considering the value of 50% for consumpt ion, the amount of carbon released to the atmosphere as gases was 69 Mg ha( -1). The amounts of CO2 and CO released to the atmosphere by the burning pr ocess were then estimated as 228 Mg ha(-1) and 15.9 Mg ha(-1), respectively . Observations on fire propagation and general features of the slash burnin gs in the test areas complete the paper.