Influence of plant spacing and genetic material on wood density and stiffness in Eucalyptus stands

Abstract

Plant spacing between the trees is a major factor in determining tree growth and wood quality, once the productivity of most forest plantations is defined by the supply or capture of sunlight, water and nutrients. Although the effect of low planting density in the variation of tree and wood characteristics has been already reported, the effect of intensive initial densities in plantations has not been fully assessed yet. Thus, the aim of this study was to better understand the effect of initial plant spacing and genetic material on the spatial variation of basic density and stiffness of the wood from 12-years-old Eucalyptus clones. The sample of this study consisted of 36 trees, 4 Eucalyptus clones planted in three different plant spacing (3 m x 3 m; 3 m x 4 m and 3 m x 8 m). For the basic density of the wood, six discs were cut along the trunk of each tree, being at the base (0), diameter at breast height (BH, at ~1.3 meters), 25, 50, 75, 100% of the commercial tree height. For the stiffness, one log from each tree was used. Near infrared (NIR) calibrations was developed for basic density and stiffness and were used to predict that properties in all samples. The NIRS technique associated with PLS-R was able to predict the basic density and stiffness, with coefficients of determination in the cross-validation (R2cv) of 0.72 and 0.70, and in the prediction (R2p) of 0.73 and 0.79 respectively. The higher the plant spacing between the trees (3 x 8 m), the greater the magnitude of radial variation. The smaller variation was found in the plant spacing 3 x 4 meters. The radial increase in the basic density in the 0 and 50% heights of trees planted at 3 x 4 m was significantly lower than those planted at 3 x 8 m. The results showed that there was an effect of the plant spacing on the radial variation of wood density at heights 0 and 50%. In relation to the effect of the genetic material, it was observed that only at 25% height the values of basic density were statistically different, with the highest values observed in clone i144 lower values in clone i182. For the stiffness, the values had the same behavior of the basic density, however, there was no effect of the genetic material and plant spacing.