Characterization of the variability of the diameter distribution of natural Taurus cedar stands in Türkiye using Johnson's S_b distribution

ABSTRACT

Background:

This article aims to provide information on the diameter distribution of naturally regenerated forests of Taurus cedar (Cedrus libani A. Rich), a tree species endemic in the mountains of the Eastern Mediterranean basin and assess their prediction ability with the Johnson S_B distribution. Previous research attested to the flexibility of Johnson family distributions to mimic empirical diameter data for a large set of tree species, justifying its use for the case study. A set of 134 plots (400 m²) were sampled in the most represented areas of the distribution of the species in Türkiye and diameter at breast height was measured in all the living trees. The cedar forests displayed heterogeneous diameter structures with diameters range from 10 to 116 cm and irregular shapes (e.g. unimodal, bell-shaped, left- and right-skewed, and non-uniform). Over three-quarters of the empirical diameter distributions (104 sample plots) were classified as S_B distribution. The remaining were classified as bounded at the lower end, S_L (16) or unbounded, S_U (14). The authors essayed the 3-parameter and 4-parameter recovery methods after Parresol and Fonseca and other´s fundamental studies. The 3-parameter recovery method outperformed the 4-parameter method in the convergence criterion and error index (EI) expressed in the basal area.

Results:

Results show that the Johnson S_B distribution can adequately reproduce the high variability in diameter for most of the distributions observed in these natural forests, providing reliable estimates which can serve as a basis for decision support systems.

Conclusion:

The S_B distribution can represent the diameter distributions of natural cedar forests, even if the empirical distributions are not in the region covered by this distribution.

Keywords:
Taurus cedar; structural diversity; parameter recovery; stand attributes; forest management