Effects Of Different Tending And Thinning Intensities On The Stand Structure Of Natural Secondary Forests In The Greater Xing'an Mountains

This paper takes the natural secondary forest of Larix gmelinii in the Greater Xing'an Mountains,Heilongjiang as the main research object and explores the effects of different tending and thinning intensities on the structure of the natural secondary forest of Larix gmelinii in the Greater Xing'an Mountains.Three plots of 0%(control check CK),16.7%(low thinning intensity LT),35.5%(middle thinning intensity MT),and 59.9%(high thinning intensity HT)tending thinning were selected,totaling 12 plots,and 7,9 and 11 years after tending thinning field survey of plots.By analyzing the horizontal structure,spatial structure,intra-forest competition relationship,forest layer structure,forest separation width and other indicators under different thinning intensities.Establish a stand structure evaluation model,construct a stand structure simulation optimization function,and explore the optimal thinning intensity of a natural larch secondary forest.(1)The natural secondary forest of Larix gmelinii has a single tree species composition,and the average proportion of larch is 79.86%.In the growth structure,the average MT of the individual plant is higher than(LT/HT)(57.89%/20%);the average annual MT of the tree height is higher than(LT/HT)(18.65%/9.48%);The amount of change MT was higher than(LT/HT)(14.36%/3.76%).In the diameter structure,the estimated value of the shape parameter c of the Weibull function is between 1.4568 and 2.5863;the change in the thinning intensity of the tending did not significantly change the diameter of the plot.(2)By comparing and analyzing the spatial structure parameters of natural secondary forest stands of Larix gmelinii under the two calculation methods,it is concluded that W and U have high consistency and correlation under the two calculation methods,and both are effective indexes.In different years,M first increased and then decreased with the increase of thinning intensity,and reached the maximum value at MT(0.341/0.358).As the thinning intensity increases,U decreases first and then increases,and the minimum value is obtained under MT(0.189/0.184).At this time,the size and spatial configuration of the forest are optimal,which is conducive to the growth of the forest.The Delaunay triangulation calculation method calculates W(0.498)at the time of MT,which is closer to a random distribution.The effect of LT on the stand structure is not significant.HT is not conducive to the stability of stand structure and the improvement of stand productivity.MT effectively improved the stand structure and increased the space for tree growth and development.40%thinning intensity can be tried as a reference index for natural thinning forests of Larix gmelinii forest in the Greater Xing'an Mountains.(3)As the intensity of tending and thinning increases,the forest competition in the plot gradually decreases,and the vertical layering of the stands is not ideal.The layering probability of each layer is less than 50%.The internal forest layer is relatively simple and vertical.The openness values of the plots S1-S12 ranged from 0.42 to 0.75,and there was sufficient space for tree growth in all plots.(4)The overall evaluation levels of the plots S1?S12 are 2,3,and 4.Among them,S7 and S9 are 4 levels,S1,S2,S10,and S12 are 2 levels,and S3,S4,S5,S6,S8,and S11 are 3 levels.After 9 years of tending and thinning in sample plot S7,the level of mixing between S7 and S9 increased after 35.5%tending and thinning,and the horizontal distribution pattern tended to be randomly distributed.The internal competition pressure of the stand was low,which resulted in more hierarchical heterogeneous forest structure.(5)Construct and optimize the simulation function to optimize the S1?S3 plot.The optimized simulation function target value V of sample S1 achieved the maximum value of 27.6822 at 30%thinning intensity;the values of V of S2 and S3 achieved the maximum values of 36.3754 and 37.1553 at 40%thinning intensity,respectively.The stand density of S1 is relatively low,which is not suitable for high-intensity thinning.Simulation optimization is the best at 30%thinning.The stand density of S2 and S3 was normal,and 40%thinning intensity was the optimal thinning intensity.(6)Substitute the optimized structure stand index into the stand structure evaluation model for stand structure evaluation.The stand evaluation levels of plots S2 and S3 have changed under different simulated thinning intensities.Among them,the rating of S2 plots reaches 4 under 40%simulated thinning intensity,and the plots of S3 are 20%,30%,40%,50%.The evaluation grades at simulated thinning intensity all reached 4 grades.At S2 and S3,the stand structure evaluation indexes reached the maximum values of 0.639 and 0.682 at 40%simulated thinning intensity.The forest structure index after the optimization simulation was substituted into the forest structure evaluation model,and the levels of sample plots S2 and S3 were improved after the optimization simulation,showing the feasibility and reliability of the forest structure optimization simulation scheme.The optimal thinning intensity obtained from the optimization simulation was consistent with the results obtained from the actual thinning operation.The thinning intensity of about 35.5%is the optimal thinning intensity of the natural secondary forest of Larix gmelinii in the Greater Xing'an Mountains.