Uncertainty in the biomass of Amazonian forests: An example from Rondônia, Brazil

• Published in: Forest ecology and management 1995-07, Vol.75 (1), p.175-189
• Main Authors: Brown, I.Foster, Martinelli, Luiz A., Thomas, W.Wayt, Moreira, Marcelo Z., Cid Ferreira, C.A., Victoria, Reynaldo A.
• Format: Article
• Language: English
• Subjects: Amazonian forest; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Biomass; Conservation, protection and management of environment and wildlife; Environmental degradation: ecosystems survey and restoration; Forestry; Fundamental and applied biological sciences. Psychology; Generalities. Production, biomass. Quality of wood and forest products. General forest ecology; Production. Biomass; Uncertainty
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/0378-1127(94)03512-U

A critical factor in estimating the contribution of tropical deforestation to nutrient mobilization and to CO 2 build-up in the atmosphere is the amount of biomass available to burn. The biomass data for Brazil, a major site for deforestation, are few and of uncertain accuracy. Recent international agreements, however, require national inventories of sources and sinks for atmospheric greenhouse gases; such inventories will need better estimates of biomass and their uncertainties. To provide additional information on biomass uncertainty and on forest structure in southwestern Amazonia, a region of active deforestation, we measured in 1988 the diameter, bole and canopy heights of 474 trees covering a total of 1 ha (10 000 m 2) in the Ecological Station of the Samuel Hydroelectric Reservoir in Rondônia (845′S, 63°23′W). Using allometric equations based on destructively sampled trees, we estimated the largest biomass component, standing alive aboveground biomass (SAAB), as 285 Mg (dry weight) ha −1. Fallen trunks and litter were 30 Mg and 10 Mg ha −1, respectively. The sum of these components, 325 Mg ha −1, is an underestimate of the total biomass because the biomass of roots, vines, shrubs, and small trees was not measured. Measurement error of SAAB is ± 20%, ± 57 Mg ha −1 about the mean (95% confidence interval), as derived by a Monte Carlo simulation. The SAAB distribution among trees is highly skewed: 3% of the trees contain 50% of the SAAB. For forests of similar distributions, sampling units typically used for biomass estimates (less than 2000 m 2) will usually produce biomass estimates significantly different from those of larger units. Based on subsamples of our data, sampling units of 1000 m 2 or smaller had at least a 75% chance of being outside the confidence interval of the global mean (228–342 Mg ha −1) derived from Monte Carlo simulation. To improve estimates of SAAB in similar forests a sampling program should focus on emergent and large canopy trees, the dominant contributors to biomass.