Burning of Amazonian rainforests:: burning efficiency and charcoal formation in forest cleared for cattle pasture near Manaus, Brazil

Twelve 60-m(2) plots were cut and weighed in a clearing at a cattle ranch near Manaus, Amazonas, Brazil. Aboveground dry weight biomass averaged 369 metric tons (Mg ha(-1)) (SD=187). This corresponds to approximate to 483 Me ha(-1) total biomass. Pre- and post-burn aboveground biomass loading was evaluated by cutting and weighing, and by line-intersect sampling (LIS) done along the axis of each quadrat. Because direct weighing of biomass disturbs the material being measured, the same quadrats cannot be weighed both before, and after, the burn. The high variability of the initial biomass present in the quadrats made use of Volume data from the LIS more reliable for assessing change in the biomass of wood > 10 cm in diameter; estimates of changes in other biomass components relied on data from direct weighing. Estimates of initial stocks of all components relied on direct measurements from the pre-burn quadrats; in the case of wood > 10 cm in diameter this was supplemented with direct measurements from the post-burn quadrats adjusted for losses to burning as determined by LIS. The measurements in the present study imply a 28.3% reduction of aboveground carbon pools. This estimate of burning efficiency is in the same range obtained in other studies using the same method, but two other methods in use in the Brazilian Amazonia produce consistently different results, one higher and the other lower than this one. Charcoal made up 1.7% of the dry weight of our remains in the post-burn destructive quadrats and 0.93% of the volume in the line-intersect sampling transects. Approximately 1.8% of the pre-burn aboveground carbon stock was converted to charcoal. (C) 2001 Elsevier Science B.V. All rights reserved.