Allometric models to estimate the aboveground mass AGM, belowground mass BGM and total mass TM of juvenile trees (stem diameter at breast height DBH ≤ 5 cm, tree height H ≥ 30 cm) in open-canopy terra-firme forests after wind disturbance were developed in the Amazon. For comparison, the allometric models were also developed for a closed-canopy terra-firme forest. After six models had been compared in each forest type, the model with diameter at ground basis DGB and H was selected as the best for estimating AGM and TM, and the model with diameter at ground basis DGB as a single variable was selected as the best for estimating BGM considering the adjusted coefficient of determination and standard deviation of the mean. Models based on the diameter at breast height DBH showed poor correlation with each biomass component compared with those based on DGB for the open-canopy forest. The juvenile trees in the open-canopy forest showed higher AGM and H at a given DGB than in the closed-canopy forest, while the DGB — BGM relationships did not differ significantly between the open- and closed-canopy forests. It was concluded that the allometric models used to estimate AGM and TM were unique to each forest type. This would be because light-demanding species show higher allocation to AGM than BGM to be advantageous for competition for light by achieving rapid growth in height.