| Phoebe Zhennan is a second-class endangered tree species in China,which has high medical,economic and ornamental value.Due to unreasonable logging and imperfect management and protection measures,the wild Phoebe Zhennan resources are sharply reduced.Analysis the structural characteristics and growth law and the formulation of the optimized management plan of the stand structure are of guiding significance for the protection,management and assets evaluation of Phoebe Zhennan.In this study,we used the Phoebe Zhennan plots data which from 1989-2014 national forest inventory data in Hunan Province,The probability density functions such as Weibull distribution,Gama distribution and logarithmic normal are used to fit the diameter distribution law and analyze the diameter distribution characteristics of Phoebe Zhennan secondary forest.The binary distribution characteristics of spatial structure were analyzed by using spatial structure parameters such as complete minging index,neighbourhood comparison and uniform angle index.Species Dominance and stand spatial advantage degree were used to describe the constructive species and the overall dominant degree of stand.Comparing the fitting results of several growth theory equations for the average DBH and basal area of the stand,the highest fitting accuracy was selected as the alternative equation,and the dummy variable model of DBH and basal area growth was constructed by adding the stand types.On the basis of Reineke equation,the model of self-thinning dummy variable was built by adding dummy variable of stand type to simulate the growth and development of secondary forest of Phoebe Zhennan and the law of natural sparse,and the stand yield tables was compiled.Taking the main spatial structure parameters as the modeling variables,adopting the multiplication and division modeling idea,the objective function of stand structure is constructed,and the non-spatial structure parameters are taken as the constraint conditions to formulate the optimized management scheme of Phoebe Zhennan secondary forest structure and 3470 plot was used as a management demonstration.The results show that:(1)The diameter structure of Phoebe Zhennan secondary forest mainly obeys Weibull distribution,followed by Gama distribution,its acceptance rates are 100%and 80%,respectively.Only part of the plots obey lognormal distribution,the kurtosis and skew coefficience of diameter distribution are greater than 0,that is to say,the diameter distribution of Phoebe Zhennan secondary forest is relatively concentrated,and the distribution curve is a mountain-liking curve on the left.The diameter distribution "q"value shows that the diameter "q" value of the 10 stands is not in the range of[1.2-1.7],and the diameter structure distribution is unreasonable.(2)The binary distribution characteristics of spatial structure show that the spatial distribution pattern of trees mostly belongs to the random distribution state,and the dominant degree of trees varies greatly in the same mixed grade,most of them are in inferior position,absolute inferior position and moderate and weak species spatial isolation degree,among which the trees in random distribution but absolute inferior position account for 31.7%.In terms of the binary distribution of uniform angle index vs complete mingling,Most trees have moderate spatial isolation but random distribution,a few trees with weak spatial isolation and random distribution.Phoebe Zhennan and Cunninghamia lanceolata are the constructive species in this stand,which are absolutely dominant in the stand.The dominant degree of species is 0.423 and 0.306 respectively.(3)Logistic equation has the highest fitting accuracy for 12 and 15 site index for basal area growth,while Mitscherlich and Logistic equation have the highest fitting accuracy for DBH,the fitting accuracy of DBH and basal area growth model was greatly improved when dummy variables of stand type was added,and the fitting correlation coefficients of DBH and basal area of 12 site index were increased from 0.780 and 0.529 of basic model to 0.783 and 0.821 respectively.In the same way,the 15 site index was increased from 0.944 and 0.623 to 0.959 and 0.810,and the error of the sum of squares and root mean square of the model residuals was reduced accordingly.Comparing the fitting results of dummy variable added to different parameters,it is found that the fitting effect of dummy variable added to parameter "a" of basic model is better than that of other cases for DBH,while the best fitting effect of basal area is to add dummy variable of stand type to parameters "a" and "b" at the same time.The correlation coefficient of self-thinning dummy variable model is higher than that of Reineke basic model,the AIC and SSE value of the model are smaller than Reineke equation.The accuracy test results show that the total relative error of self-thinning dummy variable models is less than ± 5%,and the fitting accuracy is more than 95%,it's showed that the stand yield tables can accurately reflect the growth and development process of the secondary forest of Phoebe Zhennan.(4)Combining the spatial structure and non-spatial structure of the stand to demonstrate the optimal management of the stand structure,26 trees were felled,and the thinning intensity was 16.3%,the stand structure was greatly improved,the isolation degree of tree species increased,the differentiation degree of DBH size decreased,and the competition pressure on the stand decreased after thinning.The proportion of dominant species and intensity mixed,the objective function value of spatial structure increased,and the spatial dominance of Phoebe Zhennan species and the whole stand increased after thinning,which indicates this structural optimization operation activity has improved the rationality of the overall structure configuration of the stand,and the operation plan is feasible,which can provide technical reference for the quality improvement and increment of Phoebe Zhennan secondary forest in Hunan Province. |
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