Diameter Distribution Functions for Even-aged (Picea abies) Stands

1993

47 S.

38 Lit. Ang.

Bandaufführung

37967

Three types of diameter distribution functions for even-aged, pure Picea abies stands were developed: A Weibull function, a Johnson's System b (J-Sb) function, and a linear logistic function for estimating discrete distributions. The estimation data (349 plots, 1451 observations) and test data (232 plots, 746 observations) consist of information on stand characteristics and single tree diameters at several measurement occasions, most often 3-4 years apart. The basal area mean diameter, stem number, and site index is used to estimate the Weibull and J-Sb distribution parameters (multiple regression), and to estimate discrete distributions in 5 diameter classes directly (linear logistic regression). The fit between the predicted and observed distributions are tested by the Error Index and by goodness of fit tests. The difference in accuracy between the three functions is small. If distributions in 5cm classes are of primary interest, the Discrete function is acceptable. If smaller diameter classes are of interest, the Weibull of J-Sb function might be used.