Each data-gathering method has advantages and limitations. National forest inventories (NFIs), which include biomass estimates and are conducted in most of the world’s countries, are based on field plots. But monitoring those field plots is costly, so the number is limited, and results must be averaged out over the country, resulting in less-precise calculations. Satellites gather data over large areas, but although remote biomass estimates have become more accurate in recent years, they still rely on models rather than direct measurement. And for technical reasons, remote sensing tends to underestimate the biomass of dense forest and overestimate where forest cover is low. The good news is that most countries now conduct NFIs. They are still fairly recent in tropical countries, where the surge in interest stems from the need to monitor carbon stocks under international commitments, Herold said.
