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 [Achard et al., 2002, 2004; DeFries et
al., 2002; Houghton, 2003]. By using the nearly 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 [FAO/UNEP,
1981; FAO, 1995; FAO, 2001] 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.
Author: R.A. Houghton (rhoughton at whrc dot org)
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