Afforestation on degraded tropical land and isotopic chronology analysis of soil carbon

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The study site was located at Sakaerat Silvicultural Research station , Nakhon Rachasima Province, Northeast Thailand. In this site, we have been monitoring the biomass in the plantation. The object in this paper is to estimate the carbon stock changes by afforestation on grassland during 1986 to 1998 and 2012.The biomass(Above-ground part and the roots ) increased with growth, and the annual increasing values was calculated with 5 - 7tC/ha/ year in fast growing trees. On the other hand, the soil carbon decreased about 30tC/ha in comparison with grassland. Therefore, we estimated that in the fast growing trees, the carbon of 3.1-4.7 tC/ha/year was fixed in this area by afforestation. And by isotope analysis, we found that almost soil carbon in the depth of 0-5cm in the exotic first-growing plantation was changed to plantation-derived carbon from grass-derived carbon for 24 years.