The Beta, Gamma and Weibull distribution function were studied in ten hectares of a "terra-firme" rainforest (Madeireira Dois Mil Co.) in Itacoatiara, Amazonas, Brazil. Measurements were made on 2035 trees with DBH 20 cm. Functions were compared by the Kolmogorov-Smirnov (K-S) and Residual Graphic Analysis (RGA) methods. The Weibull function performed best, followed by the Beta and Gamma function, when compared by the 'D' value of the K-S test. The Weibull and Beta functions were significant at 5%, while the Gamma was not significant, according to the K-S test. No outliers were detected for the Weibull function using RGA, indicating that variances were uniform across diameter classes, suggesting good fit of this function to this site. The Beta function can be used, but presents some bias. The Gamma function is not recommended.
diameter probablity distribution; Weibull function; Beta function; Gamma function