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How much carbon emissions from farmland reclamation in China during the past 300 years?

Science China Press

Latest, the paper--Carbon Emissions induced by Farmland Expansion in China during the Past 300 Years--firstly have mining and reconstructed the historical farmland from historical records and documents about population changes, taxes, and fields; then, use the potential natural vegetation of agricultural vegetation and the secondary vegetation in the modern natural vegetation context to reconstruct the potential landscape of historical natural vegetation without human disturbances; estimate the land use change rate and the carbon density based on the coefficients for disturbance response curves in different ecosystem scenarios in subtropical and temperate regions; and finally employ a Bookkeeping model to calculate the total terrestrial ecosystem carbon emissions induced by reclaiming farmland in China during the past 300 years. The first author Dr. Xuhong Yang and corresponding author Prof. Xiaobin Jin all come from Nanjing university.

Carbon emissions related to human LUCC activities have been the most complex source of terrestrial ecosystem carbon stocks and lead to great uncertainty. The impact of LUCC on terrestrial ecosystem carbon stocks and greenhouse gas emissions has been a hot topic of current research on land-use changes. An accurate assessment of the terrestrial ecosystem carbon accounting related to human LUCC changes will help reduce the uncertainty in estimating terrestrial ecosystem carbon stocks. During the past 300 years, population and land cover in China have changed significantly. Meanwhile, a rich bundle of records about population changes, taxes, and fields have been accumulated, which can function as a credible and fundamental data sources for studies related to historical LUCC. This also renders China as a good experimental site to conduct research on the relationship between LUCC and global carbon cycle effects.

Conforming to the principle of "similar habitat, similar distribution", this research creatively use the potential natural vegetation of agricultural vegetation and the secondary vegetation in the modern natural vegetation context to reconstruct the potential landscape of historical natural vegetation without human disturbances; then, estimate the historical farmland area change rate and the carbon density based on the coefficients for disturbance response curves in different ecosystem scenarios in subtropical and temperate regions; and finally employ a Bookkeeping model to calculate the total terrestrial ecosystem carbon emissions induced by reclaiming farmland in China during the past 300 years at low scenarios, moderate scenarios and high scenarios. By using the similar method, Houghton and Hackler (2003) believes that land uses in China had motivated the land ecosystem to release 17.1~31.90 Pg to the atmosphere in the past 300 years, and Ge et al. (2008) estimated the value should be between 4.50 and 9.54 Pg while the best estimate was 6.18 Pg. However, in this research the total amount of carbon emissions from farmland expansion in China had been between 2.94 and 5.61 Pg with the median 3.78 Pg during the past 300 years; specifically, carbon emissions of vegetation were 1.58 Pg while those of soil ranged from 1.35 Pg to 4.03 Pg with the median 2.20 Pg.

The amount of farmland in China had continuously increased from 555,000 km2 in 1661 to 1,348,000 km2 in 1980, a net gain of 793,000 km2 in the past 300 years; about 65% of reclaimed farmland had been forest land and 26% of that had been grass land previously; carbon emissions vary greatly across various ecosystems: the emissions were most from forest land, and then grass land and swamps, and the least from shrubs; deserts functioned more likely to be carbon stock in the process of land reclamation; Carbon emission induced by farmland reclamation is of the distribution of "U", i.e., great in both ends while low in the middle, and had been released least in the first half of 19th century while most in the middle of 20th century. Spatially, the carbon emissions were most in Northeast China and Southwest China; Northwest China was of the least carbon emissions; and North China was of the least carbon emissions, which is probably due to its long history of agricultural production and effective practice of farming.

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This research was funded by the National Natural Science Foundation of China (No. 41671082).

See the article: Yang X H, Jin X B, Xiang X M, Fan Y T, Liu J, Shan W, Zhou Y K. 2018. Carbon emissions induced by farmland expansion in China during the past 300 years. Science China Earth Sciences, https://doi.org/10.1007/s11430-017-9221-7

https://link.springer.com/article/10.1007%2Fs11430-017-9221-7

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