Effects Of Tending Intensities On Stand Structure And Health Of Larch Natural Secondary Forests

In order to explore the effects of different thinning intensities on the structure of Larch natural secondary forests and make an accurate and reasonable evaluation of forest health,20 typical plots of Larch natural secondary forests in Daxing'an Mountains were selected as the research objects,and thinning intensities of different intensities(cutting intensities:0.00%-67.25%)were carried out to obtain stand water through field operations.Based on the index data of horizontal structure,vertical structure and spatial structure,principal component analysis(PCA)was used to evaluate the Larch natural secondary forests.Firstly,descriptive statistical analysis and difference analysis were carried out on the processed data.Then,24 indicators of the above indicators were selected to establish a comprehensive evaluation model.The comprehensive scores of 20 plots were calculated and the health grade was divided.The optimal thinning intensity range was screened out.(1)In the horizontal structure,the tree species structure is composed of Larch and birch,and the average number of larch trees accounts for 84.88%.The diameter structure of stand accords with the growth characteristics of natural forest.The diameter span of Larix gmelinii ranges from 6 cm to 30 cm,and the number of middle and small diameter steps of 6,8,10,12 and 14 diameter steps is obviously superior.The Weibull shape parameter C values of 20 plots ranged from 1.5109 to 2.6785,showing a left-sided single peak shape.After thinning,the growth structure data of all plots showed some differences.The average volume per plant of L5 plot with thinning intensity of 13.74%was 0.043 m3,and that of L7 plot with thinning intensity of 19.00%was 0.689 cm and 0.599 m,respectively.In a comprehensive view,thinning intensity of 16.75%to 20.86%was the best.(2)In the vertical structure,the gap fraction of L2-L20 plots was higher than that of control plots L1.With the increase of tending intensity,the gap fraction of all plots increased gradually.The gap fraction of all plots except L2 plots was larger than that of control plots L1,and the gap fraction(9.19%)and opening(9.56%)of L20 plots with thinning intensity of 67.25%were the maximum values;the leaf area index and average leaf inclination of all plots were the highest values.There was no obvious change in angle.Shannon-wiener index(H')(1.0633)and evenness index(J)(0.7670)of arbor layer in L19 thinning plot with thinning intensity of 59.92%,shrub layer diversity index(Hf)(1.3641)of L20 thinning plot with thinning intensity of 67.25%,and shrub layer evenness index(J)(0.9253)of L1 7 thinning plot with thinning intensity of 53.09%were the maximum values.The herb layer diversity index(H')(1.4541)and herb layer evenness index(J)(1.0489)of L19 plot with a degree of 59.92%were the maximum values.(3)In the spatial structure,the average mixing degree of all plots ranged from 0 to 0.3727,and the isolation degree of tree species was low.The average mixing degree of L11 plots with thinning intensity of 34.38%was the maximum(0.3720).The average angular scale of each plot ranged from 0.405 to 0.563,and the whole plot tended to be randomly distributed.The angular scale of L10 plot with 27.85%thinning intensity(0.563)was the maximum.The average size ratio of L8 plots with thinning intensity of 20.86%(0.5556)was the maximum,and the tending measures with different thinning intensity had no significant effect on the size differentiation of Larch natural secondary forests plots.(4)Health assessment of Larch natural secondary forests plots with different thinning intensities was conducted by principal component analysis.The results showed that L7(0.841),L9(0.825),L8(0.821),L18(0.326),L13(0.257),L20(0.238),L10(0.207),L17(0.524),L12(0.386),L11(0.062)belonged to sub-healthy plots,L16(-0.085),L19(-0.109),L6(0.238),L10(0.207),L17(0.524),L12(0.062)belonged to sub-healthy plots.(-0.139),L15(-0.249),L4(-0.267),L14(-0.337),L2(-0.361),L5(-0.458),L1(-0.643),L3(-0.896)belong to the general healthy sample plots.The L7 plot had the highest comprehensive score,and the thinning intensity of 19.00%was the most suitable for the tending and transformation of Larch natural secondary forests in Daxing'an Mountains.The research results can provide reference and basis for the subsequent tending and management of Larch natural secondary forests in Daxing'an Mountains.