| The structural attributes of forest communities are important parameters to measure the impact of forest tending management on stand growth.The ground-based handheld mobile lidar scanner（HMLS）which has the ability to quickly and accurately obtain forest structure information provides an opportunity to explore the application of lidar in subtropical forest monitoring.In this study,three natural forestry demonstration sites established by Country Field Scientific Observation Station of Zhejiang Tiantong Forest Ecological System were selected as the research objects.HMLS was used to scan the forest sample plots aiming for exploring the feasibility of existing HMLS equipment and the method of forest structure parameter extraction in subtropical forests.And further conducting a preliminary comparison and analysis of the structural parameter changes of the Yuwang plots for one year,the main results are as follows:⑴In the subtropical close-to-nature forest sample plots with complex under-forest conditions,HMLS has the ability to quickly obtain single trees and the diameter at breast height（DBH）of each tree in the sample plot.In total,1264 trees were measured on 16 plots within the study areas,and 1292 single trees were extracted by using Li DAR point cloud data segmentation.The detection rate of single trees in each plot was above90%;The coordinates and DBH of single trees were used for reasonable matching 948trees,the overall accuracy of single tree segmentation is 75.1%.Regression analysis was performed between the Li DAR estimated DBH and the measured value of all matched single woods.The estimated change of DBH and the measured change in each plot had a high correlation（R2=0.968,RMSE=1.484cm）,so it has the potential to replace traditional manual field surveys to monitor forest growth in actual research.⑵Using the point cloud data scanned by HMLS at the sample site scale can extract more accurate LAI（P>0.05）,and there is a certain difference between the extracted tree height and the estimated ground value（P=0.04）.Extracted from the point cloud data scanned by HMLS,the tree height distribution and leaf area density（LAD）vertical distribution information can describe the vertical structure of the forest stand more accurately.According to the dominant species,the plot was divided into two groups:Pinus massoniana and Schima superba stands（YW-1,YW-2）and Pinus massoniana and Liquidambar formosana stands（YW-3,YW-4）.The peak of two groups were the same.It was found that the Pinus massoniana and Schima superba mixed stands had obvious stratification,showing a single-peak distribution.And the overall height distribution of the Liquidambar-masson pine forest was relatively even with multiple peaks.The Li DAR data was further used to calculate the LAD distribution in the vertical direction of the plots.The LAD vertical distribution was roughly the same as the tree height distribution in each plot.Considering the distribution of tree height and LAD,Pinus massoniana and Schima superba stands and Pinus massoniana and Liquidambar formosana stands were divided into 3 and 4 vertical layers..（3）By comparing the changes of LAD in different forest stratifications between the treatment and the control plot in one year.The growth of the trees in the plot after thinning treatment was concentrated in the understory and sub-canopy layer,which significantly increased the leaf area of the vegetation the height by 10m in the lower forest layer.Compared with the control plot has a tighter canopy,LAD in the lower forest layer did not increase significantly.At the same time,large trees lack of growth space,in order to compete for more light,the forest trees tend to grow vertically upwards.The LAI of the thinning treatment and the control plot increased by 30.17%and 2.3%in one year respectively,Cv LAD in the treatment plots increased,but it decreased slightly in control plots.And the vertical distribution difference of LAD in treatment plot became larger,while the vertical tree height growth of the control plot was more obvious than that of the horizontal canopy growth,indicating that the thinning measures played a role in promoting the growth of the canopy during this year.⑷The growth rates of DBH in the treatment and control plots during 1 year were14.32%and 11.97%,and the growth rates of tree height were 2.17%and 2.78%,which provided that the thinning of tending can promote the growth of the stand diameter at DBH,but does not show the promotion of the growth of the tree height.In summary,it can be preliminarily concluded that the close-to-nature forest measures have a significant promotion effect on the growth of the vegetation in the middle and lower layers.However,it has the weaker impact on the tree height growth.It promotes the development of forest towards multiple levels and high volume.At this stage,close-to-nature forest management has achieved certain results. |
