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The main objective of Eucalyptus breeding programs for the pulp and paper industry is to produce varieties of trees with high levels of cellulose with the least possible amount of lignin. However, trees with these characteristics can be a major problem in the field, because of their fragility that makes them susceptible to breaking. The aim of this study was to investigate the clonal and environmental variation of the growth, wood density, and dynamic properties on large pieces of Eucalyptus wood by means of resonance technique. Here, we demonstrated that no other non-destructive technique is able to characterize the mechanical properties of wood so simply and rapidly at such low cost. The resonance technique provided a large, accurate data set of the key mechanical traits (such as the Young, the shear modulus and the loss tangent) of the wood even in lumber containing knots, small cracks and also slightly damaged areas. There were significant differences between clones and sites for height and circumference, and density of the trees. Using the dynamic elastic estimates, significant differences were detected between clones for all traits; however, no significant differences between sites were detected for dynamic modulus of elasticity. There were significant effect of interaction clone x site for circumference, height, density and shear modulus. These findings can be useful for screenings, classifications, or preliminary selections in breeding programs of Eucalyptus.