Research On Aboveground Biomass Estimation Of Populus Euphratica Based On LiDAR

Populus euphratica is the main adapted tree species in the lower reaches of the Tarim River.Furthermore,it isthe dominant vegetation main body in the oasis and desert transition zone.Populus euphratica has important functions such as resisting wind and sand,curbing desertification,enriching productivity,and maintaining regional ecological balance.It has significant economic and ecological benefits.the weakening and vigorous growth of Populus euphratica forest in the downstream directly affects the ecological environment of the entire Tarim River Basin.Therefore,it is an important task to monitor and evaluate the growth of Populus euphratica forest on a regularly.In this study,the Alagan section of the lower reaches of the Tarim River was selected as the study area,and the natural Populus euphratica forest as the study object.Five monitoring sample plots of Populus euphratica were set according to the distance from the river,and Populus euphratica was scanned by laser.Through the indoor data processing,the high-precision growth parameters of all the Populus euphratica plants in the sample plots were obtained.Based on the accuracy verification using the field measured data,the allometric growth model was used to estimate the aboveground biomass of Populus euphratica forest,and the data difference analysis was carried out.The main conclusions are as follows:(1)Based on the field measured data,the accuracy of Populus euphratica growth parameters fitted by laser were evaluated.The result is good.Theaccuracy of the DBH was R~2=0.92,and the accuracy of the tree height was R~2=0.88.Accuracy meets the requirements for analysis and evaluation of Populus euphratica growth status.(2)The single-plant segmentation of Populus euphratica based on laser point cloud data was good,showing the advantages of LiDAR technology in sparse riparian forests.The DBH recognition rate of individual Populus euphratica was 84.25%,which met the application requirements of forest resources survey.(3)The basic growth parameters of Populus euphratica extracted from LiDAR point cloud data were as follows:The average tree height of Populus euphratica in sample plotsNo.1 to No.5 were 6.53m,9.72m,7.42m,7.01m,5.97m,respectively.The average DBH were 0.21 m,0.3 m,0.23 m,0.24 m,and 0.58 m.The results showed that the Populus euphratica tree in the No.2nd sample plot which was about200m away from the river had the highest height,while trees in the No.5 sample plot with a distance of 1000 m from the river had the lowest tree height.The average DBH of per plant showed the opposite result.(4)Estimate the above-ground biomass based on the Allometric growth model,results were as follows:the total biomass of sample plots No.1 to No.5 were 5,790.93kg,5,104.49 kg,3029.739 kg,3400.445 kg,2,668.15 kg,respectively.The average biomass were 60.7466 kg,121.464 kg,73.89608 kg,77.28284 kg,206.6269 kg.The results showed that with the increase of the distance away from the river,the total biomass on the plot scale gradually decreased,while the biomass at the scale of individual Populus euphratica showed an increasing trend.(5)According to the coupling relationship between the growth parameters of Populus euphratica and water environment factors,the following conclusions are obtained:the correlation coefficient between the distance from the river channel and the total biomass of the sample was-0.910,(p<0.05),showing a significant negative correlation.the correlation coefficient between the average biomass of Populus euphratica and the average DBHs was 0.986,(p<0.05),showing a significantly positive correlation.The correlation coefficient between the number of individual plants and the distance from the river was-0.85,which was significant negatively correlated.The correlation coefficient between the number of individual plants and the total biomass of the sample plot was 0.817,which was significantly positive correlated.In summary,the number of individual plants of Populus euphratica was significantly reduced as the distance from the river increases,while DBH became larger.The number of individual plant and DBH are the main factors affecting biomass.According to the analysis of the sample plots as the main unit,the decrease in the number of individual plants of Populus euphratica caused the decrease of biomass.The farther away from the river,the lower the biomass and the weaker the productivity.