Estimation of Soil Organic Carbon Stocks in Plantation Forest Soils of Northern Taiwan

The possibility of estimating the global carbon pools on the earth has attracted scientists for decades. In Taiwan, among remaining forested areas, 14% (about 420,000 ha) are plantation forests. There are few investigations of the soil organic carbon (SOC) pool of plantation forests in Taiwan. Nine plantation tree species, including 3 broadleaf species and 6 coniferous species were selected to estimate the SOC pools in selected plantation forest soils in northern Taiwan. The uncertainty of the estimates was examined, and strategies to obtain more-precise database for SOC pool management are proposed in this study. The results showed that only 2 Soil Orders, Inceptisols and Ultisols, were found at the study sites, and values of the soil bulk density (Bd) in broadleaf plantation forests were relatively higher than those in coniferous plantation forests. The stone contents were about 17 and 14% (0~30 cm) on average in the broadleaf and coniferous plantations, respectively. The average SOC was about 28 g kg^(-1) (0~30 cm) in the broadleaf plantations and about 48 g kg^(-1) (0~30 cm) in the coniferous plantations. The SOC pool was lowest in the Aleurites fordii plantation forest and highest in the Chamaecyparis obtusa plantation forest. We calculated that the average values of the SOC pool in the broadleaf plantation forest were about 6.5 (0~30 cm), 8.2 (0~50 cm), and 9.6 kg m^(-2) (0~100 cm). In coniferous plantation forests, they were about 7.4, 9.7, and 12 kg m^(-2), respectively. Estimation of the SOC pools in this study was potentially compromised by measurement errors of soil Bd, soil volume calculations, C determinations, and the stoniness of the soils. These sources of error might have introduced a bias, when comparing SOC contents among studies in the literature where different methodologies were applied. In conclusion, we suggest that the database of lower taxonomic categories (i.e., greater detail) for Soil Taxonomy and the SOC variability within and among pedons of the same soil type strongly need estimates of soil C stocks in Taiwan.