Soil Carbon Stock Change Due to Afforestation in Japan by Paired-Sampling Method in an Equivalent Mass Basis

Abstract

To identify the soil carbon stock change from cropland to forest land in Japan, we compared the soil carbon stock of a cropland and that of an adjacent forest land at 23 different sites. With regard to a 0-30 cm depth basis, the soil carbon stock in the cropland was greater than that in the forest land; however, it was less than that in the forest land when an equivalent mass basis was used. In less than an elapsed time of 20 years after a land-use change, the soil carbon stock after afforestation was less than that in the adjacent cropland at the same sites. However, after an elapsed time of 20 years, the soil carbon stock in the afforested site exceeded that in the adjacent cropland at the same sites. The ratio of the soil carbon stock in forest land to that in the cropland was 1.10 on average, which is comparable with the previous mass-corrected paired-sampling studies. The ratio in the conifer-planted forest was significantly greater than that in the hardwood re-generated forest. Some of the previous reviews, including those of the non-mass-corrected data, were possibly biased, and more studies using the paired-sampling method with equivalent mass basis need to provide more general ratios in the future.