| As one of the important models of sustainable forest management,close-to-nature forest management has always been highly valued.The measures of close-to-nature forest management include removing interfering trees,cultivating future crop trees,improving stand structure,and utilizing natural processes to promote the development of existing low-quality forests towards close-to-nature forests.In the process of management,the dynamic changes of stand structure and future crop tree growth are important basis for evaluating the management effect and guiding the sustainable management.However,due to the limitations of traditional survey methods,it is difficult to comprehensively monitor the dynamic changes of the stand structure and the growth of different components of the future crop tree in the current research,and it is necessary to introduce multi-dimensional monitoring methods.In this study,closeto-nature forest management demonstration area in Ningbo City,Zhejiang Province was taken as the research object,and the hand-held mobile laser technology was used to obtain the multi-temporal three-dimensional point cloud data of the management plots and the control plots(unmanagement plots)in 2 ～ 5 years after the first close-tonatural forest management.Based the point cloud data,the structural parameters of the stand and the components of the future crop tree(diameter at breast height,tree height,crown projection area)were extracted,and the growth dynamic rate was calculated.Then,the linear mixed effect model(LMM)was used to compare the differences in the dynamic changes between the management and control plots,and to explore the effects of close-to-nature forest management on stand structure and future crop tree growth dynamics;the main results are as follows.Within 2 to 5 years(2019 ～ 2022)after the implementation of close-to-nature forest management,canopy cover and plant area index of the stand structure of the management plots rebounded rapidly,and the difference between the management plots and the control plots gradually decreased with the increase of management time.Specifically,the plant area index of the management plots increased by 28.7 % in 4years,which was higher than that of the control plots in 2022.Although the stand complexity of the management plots remained higher than that of the control stands in both horizontal and vertical spatial dimensions,it showed a decreasing trend with the increase of management time.Moreover,the growth of forest stands in the management plots of four blocks was higher than that of the control plots in the 4-year period.The crown area and DBH growth rate of future crop trees in the close-to-nature forest management plots were significantly higher than those in the control plots,but the tree height growth was significantly lower.Compared with future crop trees of control plots,the advantage degree of DBH growth and the disadvantage degree of tree height growth of the future crop trees in the management plots did not show significant dynamic changes.Only the advantage degree of crown growth decreased significantly with the increase of management time,and the space of crown growth also decreased significantly with the increase of management time,while the crown competition index increased significantly.In addition,the ratio of tree height to diameter increased significantly with the increase of management years,and the ratio of crown area to diameter showed a significant increase to the peak value in the second to fourth year(2019 ～ 2021)after management,followed by a decreasing trend.Moreover,the dynamic changes of the ratio of tree height to diameter and the ratio of crown area to diameter of the future tree in the management plots were significantly different from those in the control plots.Based on the above research results,we found that the degree of improvement in stand structure after close-to-nature forest management decreases significantly with increasing years of management.However,the stand structure is always better than the control plots,leading to a significantly higher stand growth than the control plots.Crown area of future crop tree which is the main subject of management tends to grow in the early stages of management due to the removal of interference trees,which reduces crown competition and increases growth space.However,with the increasing years of management,the space for crown growth is reduced,and future crop tree tends to grow its diameter,strengthening mechanical support and maintaining a reasonable ratio of crown area to diameter to resist interference.Nevertheless,due to the decreased intensity of horizontal competition between the future crop tree and its neighbors resulting from close-to-nature forest management,the future crop tree can obtain more light and nutrient resources through horizontal radial growth.Therefore,the investment of the target tree in tree height growth is significantly reduced.According to the dynamic changes of investment strategy,it is necessary to utilize the competition of interference trees in the process of continuous management to increase the height of the target tree,and to remove the interfering trees on the basis of ensuring a reasonable ratio of crown area to diameter.This requires a scientific planning of the management cycle,in order to continually improve the stand structure while improving the quality of future crop tree cultivation,and promote sustainable forest management. |
