Does the Inclusion of Truncation point in a Finite Mixture Model Improve Diameter Distribution Estimation of Degraded Stand?

Abstract

ABSTRACT This study proposed an alternative approach that could be used to model irregular diameter distribution with fixed measurement threshold. Sixteen plots of 0.0625 ha size from a degraded teak (Tectona grandis L. f.) stands were used as case study, in which only trees with diameter ≥ 10 cm were considered. Four methodologies were evaluated: method 1 used the Weibull distribution neglecting the truncation point and irregularities; method 2 utilized truncated Weibull distribution; method 3 used two components 2-parameter Weibull in a mixture model, and in method 4, two components truncated Weibull in a mixture model was used. The models were assessed with different indices including Kolmogorov-Smirnov and Anderson-Darling statistics. Relative rank sum of the models was analyzed with one-way analysis of variance. The result showed that model developed with method 4 had the smallest fit indices and relative rank which was significantly different from models obtained with other methods. It also had the smallest root mean square error (5.146 m3 ha−1) and critical error (1.362 m3 ha−1) for estimating stand volume in diameter classes. Thus, incorporating truncated Weibull in a finite mixture is the best strategy for modeling diameter distribution of degraded teak stands with fixed measurement threshold.