Study On Structure And Growth Law Of Betula Platyphylla Secondary Forest In Daxing’anling,Inner Mongolia

This thesis takes the secondary middle and young Betula platyphylla forest in Daxing’anling,Inner Mongolia as the research object,selects 16 sample plots with the same site conditions,obtains data through field investigation,analyzes the structure and growth law of the Betula platyphylla secondary forest in combination with Excel and MATLAB software,and puts forward the corresponding stand structure adjustment scheme,so as to provide a reference for the scientific management of Betula platyphylla secondary forest in Daxing’anling.The main results are as follows:（1）In the study on the growth model of DBH,tree height and volume of Betula platyphylla secondary forest,taking age as the input vector and DBH,tree height and volume as the output vector respectively,the neural network models show good fitting effect and low root mean square error.The RMSE values of DBH neural network model are 0.5794,0.7310,0.7751 and 0.6949 respectively;The RMSE values of tree height neural network model are 0.6329,0.1743,0.1416 and 0.1380 respectively;The RMSE values of volume neural network model are 0.0003,0.0008,0.0009 and 0.0008respectively.（2）The maximum continuous annual growth and average growth of DBH appear in the 10^thyear,0.6cm/a and 0.43cm/a respectively;the maximum continuous annual growth and average growth of tree height appear in the 15^thyear（0.37m/a）and in the 35^thyear（0.31m/a）respectively;and the maximum continuous annual growth and average growth of volume appear in the 35^thyear,0.00034m³/a and 0.00024m³/a.（3）There are many concentrated small-diameter trees in the young forest,and the number of trees with a diameter of 6-10cm accounts for 85.6%of the total,which is conducive to stand regeneration;The number of trees with a diameter of 10-30cm in the middle-aged forest accounts for 75.6%of the total.The diameter structure of all sample plots does not obey the exponential distribution,and the largest number of sample plots obey the lognormal distribution.Therefore,the lognormal distribution is relatively in line with the distribution law of diameter in this area,and the tree height structure of middle-aged and young forests is similar to the normal distribution.（4）In terms of stand spatial structure,the middle-aged and young forests are normally distributed with the uniform angular index w=0.5 as the axis,and most trees in the stand are in the state of random distribution;The combined frequency on the left side of the axis（w=0.5-1.0）is higher than that on the right side（w=0-0.5）,and some individuals in the stand are in cluster distribution.The frequency value of neighborhood comparison is mainly distributed in three grades:u=0.5,u=0.75,and u=1.0.The individuals in the stand are mainly in the state of moderation,sub-inferiority and inferiority.When in the same uniform angular index,most trees are in the state of zero degree mixing,indicating that the degree of stand mixing is low and the tree species structure needs to be adjusted.（5）According to the current situation of Betula platyphylla secondary forest in Daxing’anling,considering the ecological benefits and economic basis,the forest structure is adjusted through tending and replanting,the trees with unreasonable structure are thinning out,and the Pinus sibirica and Picea asperata suitable for local growth are replanted,so as to optimize the design for promoting the sustainable management of Betula platyphylla secondary forest.