Estimation of soil organic carbon stock in subtropical forest region based on digital soil map in Taiwan

In Taiwan, detailed forest soil survey was conducted by Taiwan Forestry Research Institute (TFRI) from 1993 to 2002. Based on a detailed Digital Soil Map (DSM) with a scale of 1: 25,000 and an observed Soil Organic Carbon (SOC) database, the objective of this study was to estimate the SOC stock of Laoulongshi Forest Working Circles (LLS-FWC) as a case study in Taiwan. The soil map was composed of 23 soil series, 62 mapping units and 585 polygons in total area of 47,760 ha. The assumption of this study is that the 585 polygons were considered as "new soil point data" in the study area. The spatial distribution of SOC was calculated by the simple kriging method and the DSM of SOC was produced by ArcGIS. The results showed that the Gaussian model was the best fitted model of the semivariogram (R-2 = 0.71-0.86). The coefficient of determination (R-2) between actual and estimated SOC values was about 0.36. In conclusion, the estimated SOC stock in area was about 7.30 Tg in 0-30 cm, 8.94 Tg in 0-50 cm, or 10.9 Tg in 0-100 cm, respectively.