Effects Of Thinning On Larix Olgensis Plantation Stem Form Based On TLS

Thinning is an important forest management measure in the process of plantation management.Stem form is an important factor that affects the volume of trees and the yield of wood species.Terrain Laser Scanning can obtain the information of forest survey without destruction,and has broad application prospects in forestry research.This study took Larix olgensis plantation with 5 different thinning schemes set up in Mengjiagang Forest Farm,Jiamusi City,Heilongjiang Province as the research object.The sample site is scanned by ground-based laser radar.After preprocessing,the cloud data of the sample site is divided into individual trees and separated from individual tree branches,and extract parameters such as DBH,tree height and diameter at different heights of single tree from point cloud data of individual tree,Calculate various stem form indexes such as breast-height form factor(f_1.3)、breast-height form quotient（q₂）and volume distribution of different parts of stem.Analyze the influence of different thinning schemes on the stem form of Larix olgensis.The trees are divided into three grades:large,medium and small to reflect the impact of different thinning schemes on the stem form of trees of different sizes in the same stand.And retical timbering was carried out for the stands with different thinning measures,and the impact of different thinning schemes on the economic value of the artificial Larix olgensis stands was analyzed.Research indicates:（1）The accuracy of single tree segmentation based on ground-based laser radar data is high,and the accuracy of single tree segmentation is above 95%,and different thinning schemes have no impact on the segmentation accuracy.The matching accuracy of the single point cloud data obtained by segmentation and the measured data of the sample plot is high.After manual matching correction,the matching success rate reaches 99.2%.（2）Ground-based laser radar has high extraction accuracy for single tree parameters,with the average error（ME）and average absolute error（MAE）of DBH only-0.39 and 0.61,and the average absolute error percentage（MAPE）only 2.86%.The extraction accuracy of tree height is slightly lower than DBH,with the average error（ME）of-0.26,the average absolute error（MAE）of 0.715,and the average absolute error percentage（MAPE）of 3.12%.At the same time,the test results of the volume obtained by ground-based lidar also show that the lidar point cloud data has a high accuracy in the extraction of single tree parameters,and has achieved good results in the simulation of tree stem form.（2）All the thinning schemes can improve the DBH and volume of trees,but there is no significant difference in tree height between different thinning schemes（P≥0.05）;The stem form indexes of trees,such as form factor(f_1.3),breast height form quotient（q₂）and volume distribution mode,are different in different thinning schemes.Different thinning schemes have no significant impact on the root tension of trees（P≥0.05）.Under the same thinning scheme,except that the slend is significantly affected by the diameter at breast height,there is no significant difference in stem shape between trees of different sizes in the stand（P≥0.05）.（4）Different thinning schemes can improve the yield of commercial timber and large and medium diameter timber,of which the yield of medium diameter timber is the largest.Different thinning schemes have different effects on the economic value of the stand,among which thinning scheme 5（thinned with high-intensity for 2 times）>thinning scheme 3（thinned with medium-intensity for 3 times）>thinning scheme 2（thinned with low-intensity for 4times）>thinning scheme 4（thinned with medium-intensity for 2 times）>thinning scheme 1（control group）.This study further verified the potential of ground-based lidar application in stem shape research,and could provide reference for selecting different thinning schemes for Larix olgensis plantation in Heilongjiang Province.