The question of the carbon sequestration benefits of forestry projects through increases in the levels of carbon in the soil has been controversial since the Kyoto Protocol permitted forests as a carbon offset tool. While one study will not put the issue to rest, a recent report from researchers at a university in Yangling, China, suggests that some of the results suggested by intuition do occur, at least in Shaanxi Province, China.
The researchers compared farmland plots to adjacent forest plots that had been established on farmland 18, 24, 48, 100, and 200 yr previously. They found a nonlinear accumulation of total soil organic carbon in the 0–80 cm depth of the mineral soil across time. The carbon accumulated more rapidly under forest stands aged 18 to 48 yr than under forest stands aged 100 or 200 yrs. The rate was also greater in the 0–10 cm depth than in the 10–80 cm depth.
While one study does not make a global proof, the results suggest that more research using a similar methodology could be very useful in establishing more precise guidelines for sequestration of carbon in the soils of planted forests. In addition, they give encouragement to those undertaking afforestation and reforestation projects that the soil sequestration benefits that may be considered part of the project are in fact real and that there is a large potential for sequestration of carbon in the soils of planted forests.
The study is available in the peer-reviewed online science journal PLoS ONE at http://www.plosone.org/article/info:doi/10.1371/journal.pone.0032054#s3