Calculating forest biomass changes in China.

Changes in China Fang et al. (1), using forest inventory data to estimate changes in forest biomass carbon storage in China during the past 50 years, demonstrated that China’s carbon storage in living forest biomass has increased since the 1980s. We appreciate their valuable effort; however, the equation used to estimate forest biomass [note 20 in (1)] is questionable. Fang et al. purportedly divided forests into 31 provinces, three site classes in each province, and five age classes in each site class. However, site classifications have not been available in any Forest Resource Statistics of China since the 1950s. It seems impossible for the authors to have performed their calculations without the required site class information. We suspect that the equation actually used did not rely on site classes or even age classes, contrary to the presentation by Fang et al. (1). Because the factor used in the paper, biomass expansion factor (BEF)— defined as the ratio of all stand biomass to living stock volume— did not vary with ages, site class, or province, the equation cited can in fact be simplified to