Research On The Gap Characteristics Of Desert Riparian Forests Based On Terrestrial Laser Scanning(TLS)

Forest gap is a common type of small-scale disturbances in the forest ecosystems,it is also the main driving force for forest regeneration and succession.The rapidly and accurate determination of the border tree parameters and dynamics of the forest gap is a major difficulty research question.The traditional tree measuring methods is squander time,wasting manpower and cost expensive.It is difficult to ensure the accuracy of the measurement data due to the site conditions and the subjective influence of the surveyor.In this study,Terrestrial Laser Scanning(TLS)technology was used to scan the natural Populus euphratica forest in the middle reaches of the Tarim River to obtain the relevant gap parameters such as tree height(TH),diameter at breast height(DBH),crown diameter(CD),crown area(CA),and crown volume(CV).The correlation analysis was performed to obtain the following result:(1)The TLS point cloud data have a very small difference with the manually measured data.The fitting degrees R2 of DBH,TH,CD extraction are 0.911,0.842,and 0.794;TH values obtained by TLS are more accurate than manually measured data;Compared with traditional manual measurement methods,the TLS point cloud data can more conveniently obtain the forest gap size and is not easily affected by the complexity of the tree canopy shape.(2)The DBH value of gap border trees of natural P.euphratica forest in the middle reaches of the Tarim River have a positive correlation with TH,CD and CV,the correlation values are 0.64,0.68,and 0.69;The TH of P.euphratica forest has a positive correlation with the CV and CA.The comparison shows that the influence of DBH value on the tree canopy is more obvious than the TH.(3)After comparing several artificial forest gap calculation methods such as ellipse method,siogon method,equiangular elliptic sector method,etc.,the more complex the calculation model,the more accurate the area of the forest gap can be obtained;Compared with manual measurement methods,the point cloud data obtained by lidar can obtain the area value of the forest gap more directly and efficiently,and is closest to the true value of the forest gap area.(4)Directly use the TLS point cloud data calculates the shape index,sub-dimension,elongation,and openness of the canopy gap,which can relatively easily obtain the high-precision shape parameter values of the canopy gap;The shape parameters obtained from the point cloud data obtained by the ground Li DAR.It can be seen that the shape index,elongation,and openness of the forest gaps in the natural P.euphratica forest in the middle reaches of the Tarim River increase as the distance from the river channel increases.At the same time,the average tree height of the border trees shows a slow decreasing trend.In summary,using TLS can quickly and easily obtain high-precision 3D data of forest structure,which can substitute the traditional tree measurement methods that are labor-intensive,cost-intensive and time-consuming.TLS can provide high-precision information for monitoring the tree growth of P.euphratica riparian forests,and provide a useful tool and scientific basis for the effective protection and sustainable management of desert riparian forests in arid areas.