Allometric equations for estimating tropical forest biomass (Brown et al., 1989) were developed for mature forests by the IPCC. The equations provide the basis for estimating the impact of tropical deforestation on the global carbon cycle. But such equations significantly underestimate biomass carbon in young tree vegetation that occupies about 72% of the original tropical forest area. New allometric equations developed by Ketterings et al. (2001) for young secondary forests and fallows in Indonesia result in biomass estimates that only approximate those obtained using the equation by Brown et al. (1989). The use of these equations plus new hard data have changed the image of Indonesia, which has to be regarded a net carbon sink instead of a net carbon source (Van Noordwijk et al., 1995).
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