The influence of initial stand density, genotype, propagation method and physiologically aged cuttings on outerwood dynamic modulus of elasticity ( E) of 17-year-old Pinus radiata was examined at a Nelder spacing experiment in Canterbury, New Zealand. Outerwood dynamic modulus of elasticity was determined using the stress wave method on 385 trees in one Nelder plot. The experiment incorporated three genetic breeding series (850, 870 and 268 series), two propagation methods from the 268 series (seedlings and cuttings) and two different physiologically aged cuttings (cuttings taken from 1-year-old and 3-year-old parents) grown at 10 different initial stand densities ranging from 209 to 2551 stems ha −1. Dynamic modulus of elasticity was significantly influenced by initial stand density ( P < 0.0001) and genotype ( P < 0.0001), but not their interaction. Dynamic modulus of elasticity increased by 39%, from 5.4 to 7.5 GPa, between 209 and 2551 stems ha −1, with the majority of this increase (33%) occurring between 209 and 835 stems ha −1. The 3-year-old cuttings exhibited the highest E of 7.7 GPa, which significantly exceeded E for the 1-year-old cuttings, and seedlings from the 870, 268, and 850 breeding series by 15, 17, 22, and 26%, respectively. Stem slenderness (height/diameter) exhibited the strongest relationship with E ( r 2 = 0.49), displaying a significant ( P < 0.0001) positive linear correlation. Dynamic modulus of elasticity also exhibited a significant ( P < 0.0001) positive linear relationship with green crown height ( r 2 = 0.46) and a significant ( P < 0.0001) negative linear relationship with diameter at breast height ( r 2 = 0.44). The final path analysis model included stem slenderness and green crown height as significant positive direct influences on E explaining 53% of the variance in the dataset. Tree diameter and height were indirectly associated with E through their significant direct relationship with stem slenderness and green crown height. This study demonstrates the strong influence of initial stand density on E and suggests that the use of physiologically aged cuttings of greater maturation status improves E. Results also strongly suggest that the effects of diameter and height on E are mediated through stem slenderness and green crown height.