Origin-based Biomass Equations Of Larix Gmelinii And Pinus Koraiensis In Northeast China

After implementing the natural forest protection project,China’s future demand for timber will highly rely on plantation forests.Larch(Larix gmelinii)and Korean pine(Pinus koraiensis)are the main afforestation tree species in northeast China.Their population have been massively increased after a large number of intensive afforestation projects applied by China’s central authority.Plantation forests can provide vital material supplies and ecological services for human society and are essential for sustainable forest management.However,the forest plantation’s biomass has been drastically changed due to numerous human activity and natural disturbances,creating uncertainties in global forest carbon measurement.Hence,more comprehensive models are needed to appropriately understand the allometric relationship variations between the two origins(i.e.,plantations and natural forests).A total of 301 trees of Larix gmelinii and 63 trees of Pinus koraiensis were destructively sampled from plantations and natural stands across northeast China.The data was used to construct the additive systems of general(GM)and dummy variable(DM)models using weighted nonlinear seemingly unrelated regression(NSUR)to investigate the effect of forest origin on tree components and total biomass equations.Three different combinations of predictors were used in the two additive systems(i.e.,GM and DM)for Larix gmelinii and Pinus koraiensis.Each biomass equation has its own specific weighting function to achieve the homoscedasticity in model residuals.Biomass partitioning,root-to-shoot(RS)ratio,and carbon concentration between the two origins of both Larix gmelinii and Pinus koraiensis were also analyzed in this study.The results indicated that:1)The differences between the planted and naturally regenerated trees biomass were found to be significant for the two species,and the additive system of origin-based dummy variable model(DM)clearly outperformed the general additive model(GM)according to their respective predictors’ combinations.2)Based on the Jackknife models’ validation,the two additive systems delivered good biomass predictions,of which the best models’ R2 for root,stem,branch,foliage,and total biomass equations were respectively 0.939,0.987,0.910,0.878,and 0.989 for Larix gmelinii;and 0.958,0.977,0.975,0.930,and 0.989 for Pinus koraiensis,respectively.3)Biomass allocations were varied between the two origins,and the RS ratio was higher in natural forests compared to plantations for Larix gmelinii(0.32 cf.0.25),while the result was vice versa for Pinus koraiensis(0.25 cf.0.28).4)The mean carbon concentrations of root,stem,branch,and foliage for Larix gmelinii were 46.9%,46.7%,47.6%,and 48.2%;and for Pinus koraiensis were 48.3%,47.7%,49.0%,and 49.3%,respectively.The mean carbon concentration was higher in natural forests compared to plantations for Larix gmelinii(47.21%cf.46.03%),while the result was vice versa for Pinus koraiensis(48.29%cf.48.75%).Overall,the newly developed additive systems of both origin-free and origin-based biomass models can deliver more accurate individual tree biomass estimations for Larix gmelinii and Pinus koraiensis.The research results provide reliable theoretical and technical support for the national carbon storage monitoring of China.