Challenges to Estimating Carbon Emissions from Tropical Deforestation

An accurate estimate of carbon fluxes associated with tropical deforestation from the last two decades is needed to balance the global carbon budget. Several studies have already estimated carbon emissions from tropical deforestation, but the estimates vary greatly and are difficult to compare due to differences in data sources, assumptions, and methodologies. In this paper, we describe the different estimates and data sets, and the various challenges associated with comparing them and with accurately estimating carbon emissions from deforestation. We also performed a simulation study over legal Amazonia to illustrate some of these major issues. Our analysis indicates that long-term pools of carbon, particularly the decay of product and slash pools as well as the fluxes from regrowing vegetation could accumulate and become the dominant carbon fluxes in later time periods. Therefore, it is important to consider the complete land-cover dynamics following deforestation (including transitions from forest to agriculture, to fallow, and subsequent re-clearing of fallow or secondary vegetation). The significance of these long-timescale carbon pools suggests that it is crucial to include historical land-cover changes in any present-day analysis of carbon fluxes. For Amazonia, our simulations suggest that we need to include historical changes for at least the previous 20 years; this result is, however, shown to be highly sensitive to estimates of the partitioning of cleared carbon into instantaneous burning versus long-timescale slash pools. The case study also showed that carbon flux estimates based on “committed flux” calculations, as used by a few studies, are not comparable to the “annual balance” calculation method used by other studies. Based on these discussions, we propose a “checklist” of key issues to enable more accurate and comparable estimates in the future of carbon fluxes from tropical deforestation.JRC.H.3-Global environement monitorin