Abstract: [Objective] In order to improve the monitoring efficiency and precisely calculate forest carbon sequestration in afforestation projects in Guangdong Province,this study selected major broad-leaved tree species in Guangdong,such as Cinnamomum camphora,Schima superba and Liquidambar formosana,and established aboveground biomass models with age and diameter as independent variables.[Method] All 270 sample trees with 90 sample trees for each tree species were obtained according to 10 diameter classes during the process of modeling,using destructive experiments and stem analysis method to obtain tree biomass and age data.Using the dummy variable method to distinguish the different origins (natural forests and plantations),single tree biomass models with the diameter of breast height (DBH) and age were established for the three species.Also the aboveground biomass components (stem wood and bark,branches,foliage) were established for natural forests and plantations based on dummy variable method.The additivity or compatibility of the components of the aboveground parts was solved by the nonlinear simultaneous equation systems.[Result] The determination coefficients R_adj² of the three above-ground biomass models of the three tree species are between 0.89 and 0.94.It is feasible to use biomass model (1) with DBH and age to estimate tree above-ground biomass.Model (1) has good estimation result and is easy to use.After adding the dummy variable,the three above-ground biomass models R_adj² of the three tree species all reached 0.90 or more.Model (4) can further improve biomass estimate accuracy and refine the model application conditions;for the B-D-T based compatible biomass model system (7) there are good performances in 3 tree species.R_adj² of stem biomass model is between 0.90 and 0.95,R_adj² of bark biomass model is between 0.84 and 0.94,and R_adj² of branch biomass model is between 0.73 and 0.91.The R_adj² of the leaf biomass model is between 0.63 and 0.75,and a compatible B-D-T biomass model system (8) with dummy variables is constructed.The stem biomass equation R_adj² is between 0.88 and 0.97,and the bark biomass equation R_adj² is between 0.82 and 0.93,the branch biomass equation R_adj² is between 0.84 and 0.90,and the leaf biomass equation R_adj² is between 0.62 and 0.69.The result further indicate that the biomass model with DBH and age is more effective than the DBH and tree height biomass models.[Conclusion] This study established the aboveground biomass model with diameter and age for three major native broad-leaved tree species in Guangdong Province.The biomass compatibility model of each component in the aboveground biomass part was established by simultaneous equations.The single tree aboveground biomass model with the DBH and age model (1) have higher fitting accuracy than the commonly used two DBH and height model (2) and (3) and the model (4) with dummy variable also have higher fitting accuracy than model (5) and (6).The precision of nonlinear simultaneous equations (8) with dummy variables is higher than that of model system (7) with B-D-T.Meanwhile,the precision index of the dummy variable simultaneous equations (8) with the DBH and age variable is also better than that of the dummy variables simultaneous equations (9) and (10) with the DBH high variable.The simultaneous equations (8) not only ensure the compatibility between the aboveground biomass of each component,but also obtain more optimal parameter estimates from different origins.The single-wood biomass model with DBH and age (1) and the aboveground biomass model considering the origin (4),the model system (7),the biomass compatibility equations for the above-ground components with the DBH and age,and considerations the above-ground biomass compatibility equations (8) have higher fitting precision than the commonly used above-ground biomass models of DBH and tree height,and are more suitable for artificial broad-leaved forest and carbon sink afforestation projects (arbon sink measurement,monitoring and evaluation) in practice.

Key words: tree age, biomass model, dummy variable, simultaneous system of equations, compatibility, origin