Six probability density functions were used to model diametric distributions of Acacia melanoxylon, Eucalyptus camaldulensis, and Eucalyptus nitens being investigated for dendroenergy purposes at three plantation densities (5,000, 7,500, and 10,000 trees ha(-1)). The Weibull was the function with the best fit, followed in decreasing order by the beta, Johnson S-B, gamma, lognormal, and Johnson S-U functions. Planting density affected the shape and amplitude of the diametric distribution of all species. Increasing stocking made distributions more leptokurtic and narrower. Analyses over time during the first 28 months suggested a stronger effect on diameter distribution form, which was less evident during the early ages of the crop. FOR. SCI. 58(6): 663-672.