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Scientia Silvae Sinicae ›› 2019, Vol. 55 ›› Issue (10): 68-75.doi: 10.11707/j.1001-7488.20191008

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Stem Taper Function for Larix gmelinii Based on Nonlinear Quantile Regression

Yanyan Ma,Lichun Jiang*   

  1. Key Laboratory of Sustainable Forest Ecosystem Management, Ministry of Education School of Forestry, Northeast Forestry University Harbin 150040
  • Received:2017-09-18 Online:2019-10-25 Published:2019-11-26
  • Contact: Lichun Jiang
  • Supported by:
    国家自然科学基金项目(31570624);中央高校基本科研业务费专项资金

Abstract:

Objective: The aim of this study was to develop stem taper equation for Larix gmelinii in Daxing'anling based on quantile regression models, and the results were used to compare and analyze for fitting and validation of different quantiles (τ=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9)and quantile groups. Method: Stem taper data of Larix gmelinii were collected from Daxing'anling. NLP method in SAS software was used to fit Max and Burkhart segmented taper equation which was based on quantile regression (Koenker and Bassett, 1978), and the performances of all models were evaluated by use of these evaluation statistics:coefficient of determination (R2), mean absolute bias (MAB), root mean square error (RMSE), mean percentage of bias (MPB), and prediction accuracy (P%).Result: 1) The results showed that Max and Burkhart segmented taper equations could converge based on nine different quantiles (τ=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9), showing that quantile regression could provide many different quantile estimates, and predict stem profile for different quantiles. 2) The base model was similar to the models with quantile equal to 0.4, 0.5, and 0.6. Comparing with based model, we found that all of different quantile groups (3, 5, 7, 9)could improve the prediction precision. The quantile regression based on three quantiles group (τ=0.3, 0.5, 0.7), five quantiles group (τ=0.3, 0.4, 0.5, 0.6, 0.7), seven quantiles group (τ=0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 0.9)and nine quantiles group (τ=0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9)were better than the others with the same quantile groups. The quantile regression with five quantiles group (τ=0.3, 0.4, 0.5, 0.6, 0.7)were the most accurate in predicting taper equation of Larix gmelinii based on fitting statistics. 3)Model validation showed that statistical criteria of most quantile regression groups were superior to those of the base model and the individual quantile model. Relative to the base model, MPB, MAB and RMSE of five quantile combination (τ=0.3, 0.4, 0.5, 0.6, 0.7)model reduced by 13.9%, 13.9%, 13% respectively. Objective: Quantile regression models could improve the prediction precision. Based on the five quantile group (τ=0.3, 0.4, 0.5, 0.6, 0.7), Max and Burkhart segmented taper equation showed good performances on fitting and validation statistics, and was suitable for predicting stem taper of Larix gmelinii in Daxing'anling.

Key words: Larix gmelinii, nonlinear regression, quantile regression, taper equation

CLC Number: