Study On Calorific Values And Individual Tree Energy Storage Of Four Main Coniferous And Broad-leaved Tree Species In China

The development of biomass energy plantations is one of the effective ways to solve the current energy problems and realize sustainable development of forest biomass energy.As an important index for assessing energy tree species,calorific values not only reflect the efficiency of plants in fixing and converting solar energy,but also measure the level of plants in primary productivity.On the large scale,this paper takes the two widely distributed coniferous species groups(Larix,Picea)and two broad-leaved tree species groups(Populus,Quercus)as the study objects,analyzes calorific values,ash contents and difference significance of different organs of various tree species,discusses impact factors of calorific value and ash content,and establish individual tree one-and two-variable energy storage regression models.The main conclusions are as follows:(1)The calorific values and ash contents of stem wood in four tree species group showed different trends with the height of stem wood.Except for the calorific values of Picea and ash content of Populus,which decrease with the increasing height,the calorific values and ash contents of other tree species gradually decrease from the top,middle and bottom parts of stem wood.There are significant differences in calorific values and ash contents at different heights of stem wood.(2)The calorific values and ash contents of roots in four tree species group showed different trends with the size of roots.Except for the gross calorific value of the two broad-leaved tree species,which decrease with the decreasing size of roots,other calorific values and ash contents are as follows: small root > large root > root stump.There were significant differences in calorific values and ash contents between root stump,large root and small root.(3)The calorific values and ash contents of foliage,branches and stem bark of coniferous and broad-leaved trees are higher than those of stem wood and root.Mean gross calorific value and ash-freecalorific value of aboveground part were both higher than those of belowground part,while the mean ash content is roughly the opposite.There are significant differences in calorific values and ash contents among different organs of above and belowground parts.(4)The calorific value of each organ of two coniferous species is higher than that of the same organ of broad-leaved tree species,and the ash content is the opposite.The species are ranked by ash contents of whole trees as Populus > Quercus > Picea > Larix,and ranked by ash-free calorific values as Picea > Larix > Populus > Quercus.The variation coefficients of calorific values of whole trees are less than 5%,and those of ash contents are more than 25%.(5)The calorific values and ash contents of some tree species are,besides regional distribution,related to DBH(diameter at breast height),tree height and origin.There were significant differences in calorific values and ash contents of 4 tree species groups in different regions.(6)One and two-variable regression models,based on DBH and combined DBH and tree height,of individual tree energy storage of four tree species in different regions were constructed using general regression and logarithmic regression,and then the optimal models for four species were selected,which all performed well.The one-variable models can be used in practice to make the application simple and to improve the working efficiency;and the overall error can be reduced and the goodness-of-fit can be improved by establishing a separate model of different tree species in different regions.