What was done
The authors used the Chinese National Forest Resource Inventory data base, which was assembled periodically from 1949 to 1995 on the basis of information obtained from more than 250,000 plots scattered across the country, to calculate forest biomass carbon storage over this 46-year period.  Since the inventories only provided information about the commercial portion of the country's forests, however, a biomass expansion factor was needed to covert the timber volume data to whole-tree biomass data, which also included contributions from leaf, branch and root biomass.  This transformation introduced additional complexities into the overall assessment, as the biomass expansion factor was not constant, but varied with forest age, site class, stand density, and other biotic and abiotic factors.  The success of the project additionally depended on accurate assessments of afforestation, reforestation and forest destruction.

What was learned
The carbon (C) store of Chinese forests was at a high of 5.06 Pg C in 1949 (where 1 Pg or petagram = 10¹⁵ gram), due to a large area of primary forest that had a high biomass density.  From that point in time until the end of the 1970s, carbon storage in living forest biomass decreased at a mean rate of 0.022 Pg C per year, due to human exploitation that resulted in "soil erosion, widespread desertification, loss of biodiversity, land degradation, and catastrophic flooding."  After that time, however, the Chinese government implemented several "ecological restoration projects," which changed the mean yearly loss of carbon into a mean yearly gain of 0.021 Pg C per year, due primarily to increased afforestation and reforestation.

What it means
In the words of the authors, "our results provide evidence to support the proposal addressed by the Kyoto Protocol that C sequestered by afforestation or reforestation could partly offset CO2 emissions from fossil fuel consumption," and that "continuing the practice of nationwide afforestation and reforestation projects could contribute significantly to global terrestrial C sinks."  We feel it is especially significant that this optimism is generated without any reference to the additional carbon sequestration that will be produced by the aerial fertilization effect of the ongoing rise in the air's CO2 content over the coming years.  Hence, the ability of earth's forests to significantly blunt the effects of anthropogenic CO2 emissions looks good indeed.