A new estimation of carbon emissions from land use and land cover change in China over the past 300 years.

Scientific estimation of carbon emissions induced by historical land use and land cover change (LUCC) can improve the accuracy of terrestrial ecosystem carbon budget estimates and deepen understanding of the future carbon-sink potential of terrestrial ecosystems. The present study, using historical-document-based data for provincial cropland, forest, and grassland area in China, and experimental-data-based information for provincial vegetation and soil organic carbon density, re-estimates China's LUCC-induced carbon emissions for 1700-1980 using a bookkeeping model in which we updated tabulated functions for carbon losses and gains. The past 300 years have witnessed a dramatic LUCC in China. The cropland area has increased by 67.11 million ha, while the forest and grassland areas have decreased by 127.96 million ha and 16.72 million ha, respectively. Accordingly, the net carbon emissions for 1700-1980 are 6.17-12.35 Pg C, with 8.55 Pg C in the moderate scenario. Among the contributing factors, deforestation was the largest carbon source, accounting for over 90 % of the total carbon emissions. According to our estimates, over 70 % of carbon emissions were caused by harvesting wood, while <30 % were from converting forest and grassland to cropland. Spatially, for the whole period, carbon emissions in southwestern China (Chuan-Yu, Yunnan, and Guangxi), northeastern China (Liaoning, Jilin, and Heilongjiang), and parts of northwestern China (Gan-Ning, Qinghai, and Xinjiang) were as high as 6.03 Pg C, accounting for 70 % of the total carbon emissions. Extending previous studies, we updated the historical LUCC data, carbon density data, and tabulated functions for carbon losses and gains. The estimation results objectively reveal the historical spatiotemporal changes in LUCC-induced emissions.