M. Maltamo et al., COMPARISON OF BETA-FUNCTIONS AND WEIBULL FUNCTIONS FOR MODELING BASALAREA DIAMETER DISTRIBUTION IN STANDS OF PINUS-SYLVESTRIS AND PICEA-ABIES, Scandinavian journal of forest research, 10(3), 1995, pp. 284-295
The purpose of this study was to compare beta and Weibull distribution
s in describing basal area diameter distributions in stands dominated
by Scots pine and Norway spruce. The material of the study consisted o
f 535 stands located in eastern Finland. Parameters for both two- and
three-parameter approaches of the Weibull distribution were estimated
using the method of maximum likelihood. Models for these parameters we
re derived using regression analysis. For the beta distribution, regre
ssion models were formed for the minimum, maximum and standard deviati
on of diameters within individual stands. These models were used when
the exponents of the beta distribution were calculated analytically. A
lso, some parameter models for beta and Weibull distributions from pre
vious studies were compared with the measured diameter distributions.
The distributions obtained were compared using diameter sums and an es
timate of the proportion of sawtimber. The results did not reveal any
major differences between the suitability of the beta and two-paramete
r Weibull distributions. There are appropriate models available for bo
th of the distributions and the more similar the original data is to t
he data of an application, the better are the results. The two-paramet
er approach of the Weibull distribution gave better results than the t
hree-parameter approach. The poorest results for all the predicted dis
tributions were obtained at the extremes of the distributions.