| The spatial structure of the stand directly reflects the quality and future development direction of the forest,it is important to evaluate the spatial structure of stand reasonably.In this paper,the attributes of trees(DBH,Height and Crown width)are selected as the comprehensive weight,and a weighted triangular network is established to describe the spatial structure of stands.Using the C-D production function model,the production function model of stand spatial structure was constructed with the parameters of Complete mingling,Neighbourhood pattern and Angle competition index as "input" and the comprehensive index of stand spatial structure as "output",so as to define the comprehensive index model of stand spatial structure(FSSCI).The variation of spatial structure elements determined by weighted triangulation network was analyzed,and the applicability of spatial structure parameters and FSSCI of each stand was evaluated.Based on FSSCI,the forest space structure thinning model is constructed,and the multi-objective unified planning is realized,the model is applied to the optimization and adjustment of the spatial structure of the experimental sample to verify the rationality of the model.The main research results and conclusions are as follows:(1)The spatial structural elements were determined based on the weighted triangulation network.Comparing the changes of the spatial structural elements before and after the weighting,it was found that the number of adjacent trees before and after the weighting was mainly concentrated in 4-7 trees,accounting for 89.9%,and the number of adjacent trees remained the same,accounts for the largest proportion is 28.4%.Indicating that the overall spatial structural elements before and after the weighting were not changed much.The average distance difference between the center wood and the neighboring wood before and after weighting is negatively correlated with the comprehensive weight of the center wood,indicating that the difference decreases with the increase of the comprehensive weight of the center wood,the weighted spatial structure unit can reflect the interaction between trees more truly.(2)The applicability of spatial structure parameters determined based on weighted spatial structure elements was analyzed,and the analysis results showed that the data distribution of spatial structure parameters before and after the weighting conforms to normal distribution.Spearman correlation analysis results of all parameters before and after weighting showed that the total Complete mingling was significantly correlated,while the Neighbourhood pattern,Neighborhood comparison and Angle competition index were not correlated.This was because the tree position was changed after weighting,and they were all correlated with the tree position.However,the weighted spatial structural unit is closer to the true functional relationship between trees,so the parameters based on the weighted spatial structural unit can still describe the spatial structural characteristiccs and are more accurate.(3)According to the C-D economic production function,the comprehensive index model of forest spatial structure(FSSCI)was constructed,and the formula is as follows:#12The model applicability analysis shows that the FSSCI evaluation of stands before and after weighting has correlation,which indicates that the FSSCI evaluation of stands after weighting is still applicable.FSSCI can effectively evaluate both natural forest and artificial forest,and it is applicable to a wide range of areas.(4)Based on FSSCI,the optimal thinning model of forest spatial structure was constructed,and the model was solved and applied to H5 of sample plots.The optimization results were as follows:the average mixing degree of stands increased by 6.53%;The mean Angle scale was reduced by 5.3%,which was closer to the ideal value of 0.342;The average intersection competition index decreased by 8.98%.The FSSCI value increaseeed by 15.94%,indicating that the spatial structure of the stand was optimized.The thinning model optimizes the spatial structure of forest stand to the greatest extent and provides a reasonable and effective thinning scheme for forest management. |
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