Nondestructive Aboveground Biomass Estimation Of Common Tree Species In Nanning Based On Terrestrial Laser Scanning

Forest is an important part of terrestrial ecosystems and plays an important role in the global carbon cycle.Therefore,the estimation of forest aboveground biomass is of great significance for accurately assessing the function of forest carbon sinks,and also for the formulation of forest management and planning schemes.Forest aboveground biomass plays an important role in forest resource changes and carbon sinks.How to extract forest aboveground biomass accurately,efficiently and economically has always been a concern of forestry scholars.The traditional forest resources survey is mainly based on manual sampling survey,which requires manual inspection of all single trees in the plot,which consumes a lot of manpower and material resources,and need a long survey cycle.In recent years,3D Li DAR technology has been widely used in the study of extracting 3D structure of forests,Terrestrial Laser Scanning technology provides accurate 3D information of trees,including tree height,DBH,crown width,and crown volume,etc.The extraction of forest structure parameters is the premise of forest biomass estimation.In this study,Nanning Normal University Mingxiu Campus,Guangxi Gaofeng Forest Farm and Qipo Forest Farm were selected as the research areas,and four common tree species in Nanning,including Mangifera persiciforma,Castanopsis hystrix Miq,Mytilaria laosensis Lec and Eucalyptus robusta,were selected as the research objects.High-precision point cloud data was obtained by setting up Terrestrial Laser Scanning in the sample plot,and branch and leaf samples and tree core samples were collected from different tree species using branch shears and growth cones.Finally,the aboveground biomass of a single tree was obtained by combining the parameters of a single tree measured by Terrestrial Laser Scanning,which was and compared with the results of the aboveground biomass of a single tree calculated by the existing allometric growth equation.We also fitted and a new allometric growth equation to promote the estimation precision of aboveground biomass.The result showeds as following(1)Based on Terrestrial Laser Scanning,a total of 146 sample trees in 12 plots were single-tree segmented,and the segmentation rate of each plot was between 86.67%and 100%,and 136single trees were successfully segmented from 146 single trees.The success rate of single wood segmentation was 93.15%.The precision of the single-tree segmentation rate was high,which meeted the needs of forest resource surveys.(2)Based on the point cloud data obtained by Terrestrial Laser Scanning,a single tree can be completely restored.The fitting R~2 between the diameter at breast height(DBH)measured by Terrestrial Laser Scanning and the measured DBH was 0.97～0.99,and the average relative error is 1.42%～4.07%.The accuracy meets the requirements of subsequent extraction of single wood parameters and measurement of single wood aboveground biomass.(3)The above-ground biomass of a single tree calculated by the allometric growth equation was compared with that measured by Terrestrial Laser Scanning.The result showed of each organ calculated by the existing allometric growth equation was generally smaller than that by Terrestrial Laser Scanning.The aboveground biomass of a single tree measured by the allometric growth equation was also significantly smaller than the measured value of the Terrestrial Laser Scanning.The calculation accuracy of the allometric growth equation decreased with the growth of the single tree,indicating that the existing allometric growth method was not suitable.There was a certain error degree in the equation measuring the aboveground biomass of a single tree.(4)Based on the single-tree structure parameters,there was a strong correlation between DBH and tree height.Using tree structure parameters extracted from Terrestrial Laser Scanning data and stem density measured from samples,we constructed a new allometric growth equations of single-tree organ biomass and above-ground biomass with DBH as the only independent variable.The new equations reached a significant level(P<0.05),and the reconstructed allometric equation could be used to estimate the aboveground biomass of a single tree.