Effects of planting density and site quality on mean tree size and total stand growth of Eucalyptus globulus plantations

The choice of planting density is a primary silvicultural decision in plantation management which considers the trade-off between individual tree size and total stand production, affecting the type, quantity and quality of products throughout the rotation. Trends in size and production with planting density are generally well known, however, less so is the interacting effect of site quality. Consequently, a case study in which basal area and basal area growth of Eucalyptus globulus Labill. plantations on five site qualities (122–435 m 3 ·ha −1 ) planted at six densities (625 trees·ha −1 , 4 m × 4 m; 833 trees·ha −1 , 3 m × 4 m; 1000 trees·ha −1 , 4 m × 2.5 m; 1250 trees·ha −1 , 4 m × 2 m; 1667 trees·ha −1 , 3 m × 2 m; and 2000 trees·ha −1 , 3 m × 1.75 m) were used to investigate this interaction. As expected, both mean tree diameter of the whole stand and the basal area of the largest diameter 200 trees·ha −1 (D 200 trees) were higher at lower planting densities, whereas whole stand basal area was greater at higher planting densities. However, there were no significant (P > 0.32) interactions between planting density and site quality for D 200 or stand basal area, which contrasts with thinning responses in similar stands. This simplifies management considerations and suggests that trials at a given site quality may provide useful information about responses to planting density at other site qualities for the studied species.