Burning of Amazonian forest in Ariquemes, Rondônia, Brazil: biomass, charcoal formation and burning efficiency

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Biomass burning in tropical forests – the normal practice to prepare land for agriculture and ranching – has been a major source of CO 2 emitted to the atmosphere. Mass transformations by burning are still little studied in the tropics. The present study estimated parameters, such as the stock of carbon contained in the biomass, burning efficiency and the formation of charcoal and ashes in a tropical moist forest. Two sets of plots arranged in the form of `stars' (720 m 2 total) were installed in a 3.5 ha area of forest that had been felled for planting pasture at Fazenda Nova Vida, Ariquemes, Rondônia. Each `star' had six rays measuring 2 m × 30 m; alternating rays were designated for pre-burn and post-burn measurements. All above-ground biomass present in the plots was weighed directly before the burn in the pre-burn rays and after the burn in the post-burn rays. Pieces of wood with diameter ≥10 cm also had their biomasses estimated from volume estimates, using line-intersect sampling (LIS) in order to increase the area of sampling and to allow volume loss to be estimated as an increment based on individual pieces measured before, and after, the burn at the same point (as opposed to inferring change as a difference between independent estimates of stocks). The initial above-ground biomass (dry weight) before the burn was estimated at 306.5 ± 48.6 (mean ± SE) Mg ha −1, with an additional 4.5 Mg ha −1 for trees left standing. Carbon stock in the initial biomass (including trees left standing) was 141.3 (Mg C) ha −1. After burning, carbon stock was reduced by 36.8% (burning efficiency). The stocks of charcoal and ash formed in the burn were, respectively, 6.4 ± 2.7 and 5.7 ± 1.0 Mg ha −1. The destructive and nondestructive (LIS) methods did not differ significantly ( t-test, p > 0.05) in estimating post-burn stocks of wood and charcoal. The results of this study contribute to improving the estimates of parameters needed for global carbon calculations and point to ways in which estimates of these parameters could be further improved.