Changes in biomass carbon stocks in China's grasslands between 1982 and 1999

Terrestrial ecosystems in the northern latitudes are significant carbon sinks for atmospheric CO 2 ; however, few studies come from grassland ecosystems. Using national grassland resource inventory data, NDVI (normalized difference vegetation index) time series data set, and a satellite‐based statistical model, this study identifies changes in the size and distribution of aboveground biomass carbon (C) stocks for China's grasslands between 1982 and 1999. Biomass C stocks averaged 145.4 Tg C for the study period for a total area of 334.1 × 10 4 km 2 , and have increased by 17.7 Tg C (1 Tg = 10 12 g) from 136.3 Tg C in the early 1980s (average of 1982–1984) to 154.0 Tg C in the late 1990s (average of 1997–1999), with an annual increase of 0.7%. This suggests that the aboveground biomass of China's grasslands may have functioned as the C sinks in the past 2 decades. Assuming a constant ratio of aboveground to belowground biomass for each grassland type, we also estimated belowground biomass C and its change over time for each grassland type, generating an average estimate of 1051.1 Tg C for the total (aboveground and belowground) biomass C and an annual increase of 126.67 Tg C for China's grasslands over the 18 years. However, the accuracy of these estimates has limitations due primarily to uncertainties in estimates of belowground C, biomass inventories, and satellite time series data sets.