National Inventory of Soil Carbon Stock In Japanese Forest Confirmed Historical Human Impact On Soil Degradation for Hundred of Years.

Human activities have often induced severe soil degradation in the world. We compared the soil carbon stocks among eight regions having different historical human impacts in Japan, using the dataset from the nationwide forest soil inventory project. The soil survey was done by a systematic sampling protocol; a 4 km x 20 km grid over Japan and 1921 grids were surveyed. In each plot, we arranged four sub-plots within a 0.1 ha plot, and collected samples from three layers, 0-5, 5-15, 15-30 cm in depth to determine bulk densities and carbon concentrations of the soils. National average of forest soil carbon density was 6.8 kg/m², which ranged 5.0 – 8.1 kg/m² in eight regions. Soil carbon densities were small (5.0 – 6.0 kg/m²) in Kinki, Chugoku and Shikoku regions. Partly because volcanoes were rarely located and Andisols distributed narrowly in these regions, soil carbon stock would be smaller than the other areas such as Hokkaido, Tohoku and Kanto regions where humus-rich Andisols distributed widely. It is also characterized that average soil carbon concentrations of the second and the third soil layers sharply declined in Kinki and Chugoku regions. Aerial photographs of Kinki and Chugoku regions just after World War II indicated that scarcely vegetated and bald hills were predominated near urban areas. A previous study suggested that soil erosions caused by excessive forest utilization such as excavating tree stamps and roots for fuel woods occurred during 15th to early 20th centuries over these regions. The result from the forest soil inventory revealed that soil carbon in Kinki and Chugoku regions have not easily recovered even though greenery business by planting trees had successfully been conducted for about 50 years in these regions.