Biomass Carbon Measurement Mmodel of Artificial Cypress Forest in Different Sites in Hilly Area of Central Sichuan,China

The Methodology for Voluntary Greenhouse Gas Emission Reduction Projects: Afforestation Carbon Sink (CCER-14-001-V01) points out that since most carbon measurement parameters of the IPCC are derived from Europe and America, they are prone to causing uncertainties in regional carbon measurement. Therefore, local standards are preferentially adopted for standing tree biomass models. This study took the middle-aged artificial cypress forest in Jintang County of the hilly area in central Sichuan as the research object. According to the landform, soil layer thickness and slope position, three site types were selected (hilly lower slope thick soil layer Ⅰ, middle slope thick soil layer Ⅱ, upper slope thin soil layer Ⅲ). 105 sample trees were collected to determine the carbon content rate and biomass of each organ, and to construct biomass models and related parameters (BCEF, WD, RSR). The results show that: (1) The carbon content rate of cypress leaves is the highest and that of roots is the lowest. Among different sites, there is no significant difference in the carbon content rate of branches, leaves and roots (P>0.05), while there are significant differences in the trunk between Ⅰ and Ⅱ, and in the bark between Ⅱ and Ⅰ as well as Ⅲ (P<0.05). The average carbon coefficient of the whole tree is 0.4869, slightly higher than 0.4847 in GB/T 43648—2024. The carbon coefficients of the aboveground part, trunk, bark of type Ⅲ and roots of each site are lower than the national standard, while those of branches and leaves are higher than the national standard. (2) In the unary/binary biomass models, the optimal biomass models for each organ of cypress are mostly power functions, and a few are quadratic polynomials or exponential functions. Except for some organs of type Ⅲ, the binary model with W=a·((DBH)^b·H^c) has the best fitting effect. (3) The measured BCEF, WD and RSR are all higher than the default values of the IPCC. The BCEF values of types Ⅰ, Ⅱ, Ⅲ and the whole are 18.02%, 23.40%, 31.04% and 24.03% higher than the default value of the IPCC respectively; WD is 35.15%, 37.87%, 39.75% and 37.87% higher; RSR is 35.00%, 17.73%, 23.64% and 25.00% higher. This study can provide a reference for improving the carbon measurement parameter system of the IPCC and the national standard and improving the accuracy of regional forest carbon stock accounting.