Abstract

VALLEJOS-BARRA, O. S.; AEDO-ORTIZ, D.; IZQUIERDO-OSSANDON, P. N.  and  VASQUEZ-SANDOVAL, M. A.. Evaluation of Weibull 3p optimal all-parameters adjustment prodedures for horizontal structure modeling in Pinus taeda plantations. Rev. Chapingo ser. cienc. for. ambient [online]. 2009, vol.15, n.2, pp.101-108. ISSN 2007-4018.

A set of calculation procedures for estimating the three parameters of the Weibull 3P probability density function was generated, including the location parameter. The optimal parameters of the Weibull 3P probability density function for modeling the diameters at breast height in different times at different densities of Pinus taeda plantations calculated by the generated procedures were evaluated. Yearly, during eight years, six plots for each of the five plantation densities were measured. Weibull 3P parameters were estimated by four alternative methods: the maximum likelihood, the moments, the percentiles and the hybrid. The optimization procedures looked for minimizing not only the error index but also the Kolmogorov-Smirnov, Anderson-Darling, Kuiper, Cramer-Von Mises and Watson goodness-of-fit statistics. The main findings of this research were four. First, the parameter estimation method and the plantation age affect the location parameter value. Second, 45% of the calculated location parameter values were negative. In these cases, a highly significant linear relationship was found between location, scale and shape parameters. Then, the effect of a negative location parameter value was compensated by the other parameter values. Third, the percentiles and the maximum verisimilitude methods produced the smallest and largest location parameter values, respectively. Fourth, the percentiles and moments parameter estimation methods had the best adjustment accuracy. Anderson-Darling goodness-of-fit test was associated with the moments' method and the rest of goodness-of-fit tests was associated with the percentiles method for better adjustment accuracy.

Keywords : horizontal structure; parameter estimation method; Weibull 3P.

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