The Effect of Planting Espacement and Pruning on Growth, Yield and Timber Density of<i>Eucalyptus grandis</i>

SUMMARY Results of a comprehensive planting espacement and pruning experiment in Eucalyptus grandis on a low quality site are described. The climatic conditions during the growing period of the experiment are compared with the average conditions at this site and are shown to have been very unfavourable. The height growth was slightly above that for site quality VII (van Laar). It was found that mortality was independent of planting espacement or pruning treatment throughout the growing cycle. The conclusion was made that mean annual increment culminates at about 10 years of age on this site. Higher stand densities yielded a greater volume of timber, but this greater volume was entirely confined to the smaller tip-diameter classes, no increase in timber of more than 12,5 cm tip diameter having occurred. Pruning of the living crown reduced tree size, but not total volume per ha. Pole volumes and pole acceptability, however, were reduced by pruning. It was found that timber specific gravity was indirectly related to diameter, and that this relationship was not affected by espacement or pruning. Economic calculations show that it pays to plant more trees per acre if the greatest total volume yield is the object of management, and that the additional profit is proportional to the extra trees planted and to the capital invested. However, black wattle cultivation is clearly more profitable than growing E. grandis on this site.

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