The carbon balance of tropical forest regions, 1990-2005

Global awareness of the significance of the role that tropical forests play in the global carbon cycle has never been greater, but much uncertainty still exists as to the exact magnitude of this role. Here I review and attempt to synthesise the latest evidence of both the carbon source from tropical forest conversion, and the carbon sink in tropical vegetation. Tropical biome conversion is estimated to be a source of 1.3 +/- 0.2 Pg C year(-1) to the atmosphere in both periods 1990-1999 and 2000-2005, whereas intact tropical biomes were estimated to be a net carbon sink of 1.1 +/- 0.3 Pg C year(-1). The ratios of carbon source to carbon sink are very different for the different tropical continents, reflecting different rates of conversion and different area of forest cover, with tropical Asia probably a strong net carbon source and tropical Africa probably a strong net sink. The net balance of the tropical forest biomes is estimated to be +0.2 +/- 0.4 Pg C year(-1) (not significantly different from zero) over both periods 1990-1999 and 2000-2005; this result is consistent with that from atmospheric inversion models that better represent vertical CO2 profiles (+0.1 +/- 0.3 Pg C year(-1)).