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Peer Review

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Notes

The long-term net flux of carbon between terrestrial ecosystems and the atmosphere has
been dominated by two factors: changes in the area of forests and per hectare changes in
forest biomass resulting from management and regrowth. While these factors are
reasonably well documented in countries of the northern mid-latitudes as a result of
systematic forest inventories, they are uncertain in the tropics. Recent estimates of
carbon emissions from tropical deforestation have focused on the uncertainty in rates
of deforestation. By using the same data for biomass, however, these studies have
underestimated the total uncertainty of tropical emissions and may have biased the
estimates. In particular, regional and country-specific estimates of forest biomass
reported by three successive assessments of tropical forest resources by the FAO indicate
systematic changes in biomass that have not been taken into account in recent estimates
of tropical carbon emissions. The ‘changes’ more likely represent improved information
than real on-the-ground changes in carbon storage. In either case, however, the data have
a significant effect on current estimates of carbon emissions from the tropics and, hence,
on understanding the global carbon balance.