Aboveground Forest Biomass and the Global Carbon Balance

TLDR

The net carbon flux between terrestrial ecosystems and the atmosphere is largely driven by changes in forest area and per‑hectare biomass, well documented in northern mid‑latitudes but uncertain in tropical regions where estimates have focused mainly on deforestation rates. This study argues that using consistent biomass data reveals that previous tropical emission estimates have underestimated total uncertainty and may be biased. The authors compare regional and country‑specific biomass estimates from three successive FAO assessments, showing systematic changes that have been omitted from recent tropical carbon emission calculations. These changes likely reflect improved data rather than real on‑ground shifts, yet they substantially alter current tropical emission estimates and thus our understanding of the global carbon balance.

Abstract

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.