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林业科学 ›› 2021, Vol. 57 ›› Issue (11): 94-104.doi: 10.11707/j.1001-7488.20211110

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基于Copula密度函数的毛竹胸径年龄结构特征二元联合分布

刘恩斌1,姚鸿文3,任泽茜2,周国模1,*,杜华强1   

  1. 1. 浙江农林大学省部共建亚热带森林培育国家重点实验室 浙江省森林生态系统碳循环与固碳减排重点实验室 浙江农林大学环境与资源学院 杭州 311300
    2. 伦敦大学学院地理系 伦敦 WC1E 6BT
    3. 浙江省森林资源监测中心 杭州 310020
  • 收稿日期:2020-09-29 出版日期:2021-11-25 发布日期:2022-01-12
  • 通讯作者: 周国模
  • 基金资助:
    国家自然科学基金两化融合项目(U1809208);浙江省重点研发计划项目(2021C02005)

Bivariate Joint Distribution of DBH and Age of Moso Bamboo Based on Copula Density Function

Enbin Liu1,Hongwen Yao3,Zexi Ren2,Guomo Zhou1,*,Huaqiang Du1   

  1. 1. State Key Laboratory of Subtropical Silviculture, Zhejiang A & F University Key Laboratory of Carbon Cycling in Forest Ecosystems and Carbon Sequestration of Zhejiang Province College of Environmental and Resource Sciences, Zhejiang A & F University Hangzhou 311300
    2. Department of Geography, University College London London WC1E 6BT
    3. Forest Resource Monitoring Center of Zhejiang Province Hangzhou 310020
  • Received:2020-09-29 Online:2021-11-25 Published:2022-01-12
  • Contact: Guomo Zhou

摘要:

目的: 针对森林结构特征因子常用二元联合分布研究方法存在的缺陷,选择适用条件低、适应范围广、应用价值大的二元Copula分布(密度)函数构建毛竹胸径年龄二元联合分布模型,为精确测量森林结构特征因子联合分布提供参考。方法: 选取5种常用二元Copula密度函数、二元Sbb密度函数和二元Weibull分布函数对2009年浙江省177块毛竹连续清查固定样地的胸径年龄二元联合分布进行描述,对比分析各函数的测量精度;经二维频数直方图和AIC评定,选择胸径年龄最优二元Copula密度函数,并在此基础上构建浙江省毛竹胸径年龄二元Copula联合分布模型,采用柯尔莫哥洛夫检验各分布(密度)函数的拟合优度。结果: 二元Weibull分布函数的确定系数(R2)=0.990 1,二元Sbb密度函数的R2=0.736 2,二元Gumbel Copula密度函数的R2=0.984 1、AIC=19.519 6,为5种常用二元Copula密度函数中AIC最小的函数;二元Gumbel Copula密度函数、二元Weibull分布函数和二元Sbb密度函数累计值的最大偏差分别为0.015 8、0.007 0和0.078 1,在0.05显著性水平下的阈值为0.179 8。结论: 二元Gumbel Copula密度函数为测量毛竹胸径年龄联合分布的最优Copula密度函数;二元Weibull分布函数的测量精度最高,但参数比二元Copula密度分布(密度)函数多,迭代参数没有二元Copula密度(分布)函数易收敛,二元Sbb密度函数的测量精度最低;毛竹胸径年龄联合分布均服从3种分布;二元Copula分布(密度)函数适合于胸径年龄的任意边缘分布,即不需要确定边缘分布函数类型;二元Copula分布(密度)函数参数拟合不需要胸径年龄联合分布数据,只有胸径年龄边缘分布值时,应用二元Copula分布(密度)函数可得到相应的胸径年龄联合密度值,二元Copula分布(密度)函数比常用二元分布(密度)函数的适用条件低、适应范围广、应用价值大。

关键词: 毛竹, 二元分布, Copula密度函数, 生物量, 胸径年龄结构特征

Abstract:

Objective: In view of the shortcomings of the bivariate joint distribution function commonly used in the investigation of forest structure characteristic factors, a bivariate distribution(density)function with a low applicable condition, wide adaptation range and great application value was selected to provide a reference for accurately measuring the joint distribution of forest structure characteristic factors. Method: Five commonly used bivariate Copula density functions, bivariate Sbb functions and bivariate Weibull distribution functions, were selected to describe the bivariate joint density of DBH and age of moso bamboo(Phyllostachys edulis) based on 177 continuous inventory plots in Zhejiang Province in 2009, and the measurement accuracy of each function was compared and analyzed. The optimal Copula function of DBH and age was selected based on the metrics of bivariate frequency histogram and AIC. The bivariate Copula joint density model of DBH and age for moso bamboo in Zhejiang Province was established. The goodness of fit of the model was tested using Kolmogorov test. Result: The coefficient of determination(R2) of bivariate Weibull distribution function and the bivariate Sbb function was 0.990 1 and 0.736 2, respectively, and the R2 of bivariate Gumbel Copula density function was 0.984 1 with the lowest AIC value of -19.519 6. The maximum deviations of the cumulative value of the bivariate Gumbel Copula function, the bivariate Weibull distribution function and the bivariate Sbb function were 0.007 0, 0.015 8 and 0.078 1. The critical significance value was 0.179 8. Conclusion: Bivariate Gumbel Copula probability density function is the best Copula function for representing the joint distribution of moso bamboo DBH and age. The measurement accuracy of bivariate Weibull distribution function is the highest, but the number of the parameters used is more than that of those used in the bivariate Copula function. Therefore, iterative parameter of bivariate Copula function is easier to be converged. The accuracy of bivariate Sbb function is the lowest. The joint distribution of DBH and age of moso bamboo all obey these three distribution functions. Bivariate Copula function is suitable for arbitrary edge distribution of DBH and age, that is, it does not need to determine the class of marginal distribution function. When there are only marginal distribution values of DBH and age, the joint density value of DBH and age could be obtained using the bivariate Copula function. Thus, the bivariate Copula function has a wider applicability and a higher application value than the commonly used binary distribution function.

Key words: moso bamboo, bivariate distribution, Copula density function, biomass, structure characteristics of DBH and age

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