Variations in heartwood formation and wood density as a function of age and plant spacing in a fast-growing eucalyptus plantation

The heartwood formation process is little known in fast growing plantation woods. Therefore, the aims of this study were to determine how planting spacing and tree age affect the formation and proportion of heartwood and sapwood, as well as the density of eucalyptus wood. Trees from a eucalyptus clonal plantation (Eucalyptus grandis x E. urophylla hybrid) cultivated in three spacings (3 x 1, 3 x 2 and 3 x 3 m) were sampled at 14, 27, 32, 53, 64 and 76 months of age. Heartwood percentage was quantified with Dimethyl yellow indicator, while the wood density was determined by X-ray densitometry. The heartwood percentage, wood volume, heartwood density and wood density were correlated with the different growth rates. The heartwood formation process started between 32 and 53 months, regardless of spacing. The heartwood proportion doubled with increasing age in the widest spacing and increased about four times in 3 x 1 and 3 x 2m spacing. The planting spacing influenced the growth rates of the trees, but did not affect the heartwood and sapwood percentage or density. The greatest increase in density values occurred between the first year of growth (14 months) and the beginning of heartwood formation (53 months).