Analysis of spacing for spotted gum plantations for maximizing merchantable logs' volume in Southeast Queensland, Australia

Spotted gum (Corymbia citriodora subspecies Variegata) has the potential to be the major hardwood species for large-scale plantations in Southeast Queensland, Australia, but production research is limited due to the lack of age of research plots. Optimal spacing is a major subject of concern. Based on time series data from a spotted gum experiment site, growth performance was analyzed for five spacing levels: 11.3 m × 11.3 m (78 stems ha−1), 7.4 m × 7.4 m (182 stems ha−1), 5.4 m × 5.4 m (343 stems ha−1), 3.6 m × 3.6 m (771 stems ha−1), and 2.9 m × 2.9 m (1189 stems ha−1). The major objective was assumed to be to maximize total merchantable log volume. A growth model was produced, and the mean diameter at breast height (DBH) and total merchantable log volume for each spacing level at a range of harvesting ages were estimated. From the analysis, the spacing level of 5.4 m × 5.4 m was foundto be optimal for maximizing merchantable log volume to a 10-cm small-end diameter. Further analysis of mean DBH, height, and volume of the largest 200 and 250 trees from this spacing level indicates that merchantable log volume could be maximized by retaining the 250 largest trees ha−1. The total financial revenue from the best spacing level in 25 and 30 yr are predicted to be Australian dollars (A$) 13,637 and A$17,779 ha−1, respectively. If full rotation data could be obtained, more reliable models could be produced, and a more accurate financial estimate could be made