Forest biomass carbon stocks in China over the past 2 decades: Estimation based on integrated inventory and satellite data

Forests are major contributor of terrestrial ecosystem carbon (C) pools, and are thus crucial components for assessing the global C budget. On the basis of forest inventory data for three inventory periods of 1984-1988, 1989-1993, and 1994-1998, and synchronous NDVI (Normalized Difference Vegetation Index) data, we developed a satellite-based approach for estimating China's forest total biomass C stocks. Using this approach, we analyzed the changes in forest C stocks over the last 2 decades to identify the size and distribution of C sinks/sources in the forests. The total forest biomass of China averaged 5.79 Pg C (1 Pg = 10(15) g) during the study period, with an average biomass density of 45.31 Mg C/ha (1 Mg = 10(6) g). The forest biomass C density showed a large spatial heterogeneity: high in southwestern and northeastern areas, and low in the eastern coastal regions. Over the past 2 decades, the total forest biomass C stock increased from 5.62 Pg C in the early 1980s (average for 1981-1983) to 5.99 Pg C by the end of the 1990s (average for 1997-1999), giving a total increase of 0.37 Pg C and an annual sequestration rate of 0.019 Pg C/yr. The C sink appeared mainly in regions with lower C density. Both environmental changes and human activities are likely major drivers of such spatiotemporal patterns.