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Forest Topsoil Carbon Content: The Outlook for China and Beyond

Paper Reviewed
Yang, Y.H., Luo, Y.Q. and Finzi, A.C. 2011. Carbon and nitrogen dynamics during forest stand development: a global synthesis. New Phytologist 190: 977-989.

In a paper published in Global Change Biology, Yang et al. (2014) note that - as coupled carbon-climate models have predicted - a positive feedback to global warming "could be triggered if accelerated soil carbon decomposition offsets enhanced vegetation growth under a warming climate." And, hence, they say it is "crucial to reveal whether and how soil carbon stock in forest ecosystems has changed over recent decades," seeing that "soil carbon dynamics in forest ecosystems remain uncertain," as indicated by the studies of Dixon et al. (1994) and Pan et al. (2011).

In light of this urgency, and using newly-developed databases and a sophisticated data-mining approach to achieve their self-imposed objectives, the seven scientists (1) evaluated temporal changes in topsoil carbon stock across all five of the major forest ecosystems of China and (2) analyzed the effects of potential drivers of soil carbon dynamics over broad geographical scales. And what did they thereby learn?

Yang et al. (2014) report that topsoil carbon contents increased significantly within all of the five major forest types of China over the 1980s-2000s, which results suggest, in their words, that soil carbon accumulation "does not counteract vegetation carbon sequestration across China's forest ecosystems." In addition, they say that using data synthesized from 124 chrono-sequence studies conducted at various places around the world, Yang et al. (2011) had earlier observed that the rate of carbon accumulation in both vegetation and forest floor exhibited increasing trends with both mean annual temperature and precipitation across the world's secondary forests.

In light of these several findings, the Chinese researchers were able to conclude, with a strong degree of confidence, that "the combination of soil carbon accumulation and vegetation carbon sequestration triggers a negative feedback to climate warming, rather than the positive feedback predicted by coupled carbon-climate models."

References
Dixon, R.K., Brown, S., Houghton, R.A., Solomon, A.M., Trexler, M.C. and Wisniewski, J. 1994. Carbon pools and flux of global forest ecosystems. Science 263: 185-190.

Pan, Y., Birdsey, R.A., Fang, J., Houghton, R., Kauppi, P.E., Kurz, W.A., Phillips, O.L., Shvidenko, A., Lewis, S.L., Canadell, J.G., Ciais, P., Jackson, R.B., Pacala, S.W., McGuire, A.D., Piao, S., Rautiainen, A., Sitch, S. and Hayes, D. 2011. A large and persistent carbon sink in the world's forests. Science 333: 988-993.

Posted 17 November 2014