Study On Density Variation Of Tree Trunk And Biomass Estimation In The Larix Olgensis Plantation

Wood density is the most important index to measure wood quality and a highly variable wood characteristic.Wood density is also an important wood property that affects the properties of pulp and paper and some wood products,and an important determinant of a forest's ability to sequester carbon.Tree biomass is the basis of forest ecosystems,including leaf biomass,branch biomass,trunk biomass,and root biomass.Among them,trunk biomass accounts for a large proportion.Trunk biomass can also be obtained by the product of trunk volume and wood density.The estimation accuracy of wood density determines the size of the error in the estimation of trunk biomass.Therefore,it is very important to accurately calculate the wood density.Generally,the trunk consists of sapwood,heartwood,and bark.Sapwood,heartwood and bark have different densities.The estimation of sapwood density,heartwood density and bark density have important significance and influence on the estimation of wood density of trunk.A total of 35 trees were destructively sampled from three different sites of plantation,namely,Linkou Forestry Bureau of Heilongjiang Province,Tokyo Forestry Bureau,and Maoershan Experimental Forest Farm of Northeast Forestry University.The vertical changes of sapwood,heartwood,bark density and trunk density of Larix olgensis were analyzed.The longitudinal density prediction models of sapwood,heartwood,bark and trunk were constructed by Beta regression.Based on the Beta regression model,the mixed effect model of sapwood density,heartwood density,bark density and trunk density were established.The mixed effect Beta regression model was used to estimate the wood density of the trunk,and the biomass of the trunk was estimated based on the volume and the density of the trunk.The results show that:(1)The independent variables of the optimal model of sapwood density,heartwood density,bark density and trunk density were not precisely identical.Sapwood density has a good relationship with tree age(t),tree height(H),relative height(hr),and the square of relative height(hr2).The independent variables of heartwood density model were annual growth(Dt),relative height(hr),and the square of relative height(hr2).While,the independent variables of bark density model were tree age(t),annual growth(Dt),relative height(hr),and the square of relative height(hr2).Trunk density was significantly correlated with tree height(H),annual growth(Dt),relative height(hr),and relative height squared(hr2).(2)The-2LL,AIC and BIC of the mixed effect model of sapwood density,heartwood density,bark density and trunk density were less than those in Beta regression model.The likelihood ratio test results show that increasing the random effect has a significant effect on improving the goodness of fit of Beta regression model.The analysis of the optimal mixed effect Beta regression model shows that from the base to the tip of the trunk,sapwood density decreased gradually,heartwood density initially decreased and then increased regularly,bark density initially increased and then decreased gradually,and at last trunk density decreased gradually.(3)The mean value of AWD0.25H is close to AWD,with the smallest standard deviation,the largest R2,and the smaller RMSE,indicating that the trunk density with the relative height of 0.25 has the highest accuracy as the average density of the trunk.The accuracy of tree trunk average density estimation has a significant influence on the accuracy of tree trunk biomass estimation.Trunk biomass a linear relationship between predicted values and the real value.This method of estimating trunk biomass overestimates the trunk biomass of all diameters.