| Based on the principle of three-dimensional laser scanning,this paper measured 8 different forest-age and different densities of poplar plantation forests taken from the forest land of Minquan County in Shangqiu,Henan Province.All kinds of point cloud stereo images were obtained,and the tree point indicators were measured on the point cloud in HD 3LS Scene software.Analysis of the data obtained results in the following:1.Analyze the point cloud image directly,plot the distribution of poplars in the plot field within the field of view,and speculate that the instrument can plot all trees in Mature period within a radius of 70m with the measurement point centered on the condition.The smaller the density is,the larger the radius become.It is easy to achieve the statistics of the number of trees through the point cloud image.At the same time,the segmentation of the point cloud can visually observe the growth status of the trees and the contours of various canopy projections within the forest.It can determine the height of branches and dead trees of the trees,and provide quantity and position for tree pruning and replanting of dead trees,and provide accurate data on quantity and location.2.We compared the point cloud data with the traditional measurement data in some simple tree-measurement indicators like tree height,diameter at breast height(DBH),crown width and height under branches.The principal component analysis(PCA)was used to visually show the correlation between the results obtained by the indicators under the two measurement methods,and the correlations between the tree height,DBH,crown amplitude,and the lowest branches height.The results show that the data measured by the point cloud is reliable and accurate on the indicators,and is a fast,efficient and accurate measurement method.This method can increase the work efficiency by 25%and reduce the manpower consumption by 50%while ensuring the accuracy.The correlation between tree height and branches height was the largest,and the correlation between DBH and crown amplitude was greater than the correlation between DBH and tree height.3.By comparing the crown width of each plot,we analyzed the effects of planting density and forest age on crown width.It shows that the crown width is more affected by planting density.In the comparison of different plant spacings of similar tree ages,the crown width increased with the increase of plant spacing within the range of 3m-6m.When the row spacing was greater than 6m,the crown width didn’t show any obvious regularity changes.Comparing rectangular and square distribution methods,square is better than rectangle,so a 6m×6m square distribution is the most scientific distribution method.In addition,the old poplar tree shows a significant dwarf in its tree height,and the crown shape evolves from a common spindle shape to an ellipsoidal shape.4.The DBH data can be used to represent the growth status of poplars,so the growth curve of DBH changes with age of the forest is fitted.According to the growth curve,the rapid growth period of the average DBH of poplar plantation was calculated to be 2 to 20 years old.For poplars over 20 years of age,the growth rate of DBH was significantly reduced,and the increase of the DBH at the age of 26 tended to stop.5.The spatial structure of the branches or the internal structure of the canopy is a very meaningful indicator.It can be used to estimate the leaf area index,establish the light environment conditions under the forest,the efficiency of precipitation interception,and the wind resistance effect of windbreaks.This paper takes a representative 12-year-old healthy sample tree,divides its point cloud and depicts and measures its primary branch,and obtains the orientation of each branch from the plot.It can be clearly seen that the number of first-level branches on both sides of the east and west sides is similar,and the number of first-level branches on the south side is greater than that on the north side.6.The branch length and the total leaf area of the single branches sampled by the analytical wood were used to verify the reliability of the relationship between the branch length and the total leaf area of the single branches obtained from long reach secateurs sampling.The point cloud data was brought into the relationship,and the credible total leaf area and leaf area index data of the single tree were obtained.The feasibility of the method was validated by using the long reach secateurs sampling data of multiple plots to establish the relationship between branch length and the total leaf area of the single branches.The purpose of measuring the leaf area and leaf area index using a three-dimensional laser scanning method was achieved. |
