Height-to-diameter ratios (HD) are an important measure of the stability,density and competition of forest stands.It reflects the vertical growth of the trees,the vulner-ability of the forest canopy structure and influences volumet-ric production.HD ratios vary according to tree size,avail-ability of resources for growth,stand density and species composition.Data were taken from 210 trees and a regres-sion technique of generalized linear models for the HD ratio applicable for forest structure conservation was developed.The objective of this study was to model the HD ratios of dominant and co-dominant trees of Araucaria angustifolia according to morphometric,dendrometric,annual diameter increment,stand density,and age variables in three sites in southern Brazil.The results show that the HD ratio decreases with increasing age,crown area and basal area,and increases with stand density and annual diameter increment.Accuracy of the developed equations was demonstrated by the val-ues of deviation,Bayesian and Akaike criteria.The results are of interest to forest managers since they make decisions about silvicultural operations.Growth continuity and forest production indicate that any intervention should be directed at younger trees of smaller sizes,and that one of the main management factors for stand stability and growth is the formation of the stand and its capture of light.