Characteristics Of The Diameter Structure Of Natural Forests Of Torreya Grandis ’Merrillii’ In Hunan Province

Torreya grandis ’Merrillii’ is a unique rare economic tree species in China,the development of the Torreya grandis ’Merrillii’ industry in China has aroused a wave of enthusiasm in recent years.Hunan province is one of the areas where the natural forest distribution of Torreya grandis ’Merrillii’.Stand diameter structure is the most basic and important characteristic of the stand structure.Investigating and studying the stand diameter structure and the ecological habits of Torreya grandis ’Merrillii’ is the prerequisite for the conservation and utilization of Torreya grandis ’Merrillii’ resource,artificial introduction and cultivation.In the paper,the main research object is the natural forest of Torreya grandis ’Merrillii’ in Hunan Province,and the stand diameter structure,tree species composition,and stand structure characteristics of Torreya grandis ’Merrillii’has been analyzed.Three typical distribution function models of Weibull distribution,βdistribution,and Negative exponential distribution were used to fit the diameter structure of Torreya grandis ’Merrillii’ natural forest in different standard plots,different stand types,and different stand densities,and the best distribution function for predicting and estimating the growth status of Torreya grandis ’Merrillii’ was selected.The main research contents and results are as follows:(1)To analyze the tree species composition of a typical natural forest of Torreya grandis ’Merrillii ’ in Hunan Province,the results showed that Torreya grandis ’Merrillii ’was the dominant tree species in the 12 plots surveyed.Quercus L and Sassafras tzumu as the main associated species in Torreya grandis ’Merrillii’mixed forest.Although Torreya grandis ’Merrillii’has a dominant position in stand plots,natural regeneration difficult ties occurred in some plots with poor soil or poor light conditions.There were almost no naturally regenerated small-diameter Torreya grandis ’Merrillii’ trees,and there are a lot of naturally regenerated small-diameter Quercus L or Sassafras tzumu in the forest,indicating the natural regeneration ability of the stand type and associated tree species have an important influence on the tree species composition and diameter structure distribution of Torreya grandis ’Merrillii’ natural forest.(2)The diameter structure characteristics and distribution patterns of the Torreya grandis ’Merrillii’ natural forest in Hunan Province were analyzed.The results showed that:the diameter structure of Torreya grandis ’Merrillii ’ natural forest in Hunan province was widely distributed,and the maximum diameter rank is 44cm,and the number of trees with middle and small diameter rank(6-14cm)accounts for 76.9%of the total stand.With the increase of diameter rank,the tree number decreases progressively,at the same time,the overall distribution shows a reverse J-shaped distribution or a left-biased single-peak mountain,which shows obvious characteristics of different ages of the forest.The diameter distribution of each plot was significantly different,and was significantly affected by growth conditions and ecological environment conditions,and the The stand diameter class structure showed obvious polymorphism.(3)The optimal distribution function of Torreya grandis ’Merrillii ’ natural forest with different sample plots and different forest types and densities is selected by functional fitting,Chi-square test,and accuracy comparison using three typical distribution functions models,Weibull distribution,β distribution,and Negative exponential distribution.The results showed that the Negative exponential distribution functions with constant ratio q law were 75%acceptable,the q-value was between 1.2 and 1.7,and the fitting accuracy was optimal.The coefficient of determination(R2)means was 0.887,which is the best distribution function for 8 of these plots.Weibull distribution was 58%acceptable.The acceptance rate of the β distribution function is 25%.The optimal distribution function of the Torreya grandis ’Merrillii ’ pure forest is the Negative exponential distribution function with constant ratio q law.The optimal distribution function of the Torreya grandis’Merrillii’ mixed forest is the Weibull distribution function model.A fitting analysis of Torreya grandis ’Merrillii’ forest diameter structure with different stand densities showed that the stand density of Torreya grandis ’Merrillii’ had a significant influence on the diameter structure of Torreya grandis ’Merrillii ’.The Negative exponential function was the best fitting,and all of them were the best distribution functions for different densities of Torreya grandis ’Merrillii’ natural forest.The fitting accuracy(R2)of Torreya grandis’Merrillii’ with three different forest stand densities was over 0.957.Above all,the Negative exponential distribution function with constant ratio q law is the most suitable for describing and analyzing the diameter structure distribution of Torreya grandis ’Merrillii ’natural forest in Hunan Province.(4)By studying the diameter structure characteristics of Torreya grandis ’Merrillii’natural forest in Hunan Province,the optimal distribution functions model was selected.In conclusion,the Negative exponential distribution function with constant ratio q law has the strongest flexibility and the best fitting effect,which is most suitable for describing and analyzing the diameter structure distribution law of the Torreya grandis ’Merrillii’ natural forest in Hunan Province.The probability density distribution function selected in this study had certain reference value for study and describe the diameter structure characteristics of Torreya grandis ’Merrillii’natural forest under similar conditions.The results can provide a reasonable scientific basis for the optimization and adjustment of forest structure,growth prediction,and management timber forest of Torreya grandis’Merrillii’ natural forest in Hunan Province.