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The Wood From The Trees - Issue Five - Effects of spacing on growth of blue gum

CRC Technical Report 197 Effect of stocking on growth, yield, tree diameter class distribution, harvesting cost and financial return in Eucalyptus globulus pulpwood plantations by Tom Baker and co-authors provides a nice example of cross-program integration to give insights into whole-of-industry economics.

Tom and his co-authors analysed data from a total of eight stocking trials of blue gum (Eucalyptus globulus) which were planted in the mid-1990s, on sites that ranged widely in their growth potential. They looked at the effect of stocking on volume production, and on the distribution of log diameters at harvest.  Applying a model of harvesting costs arising from Program Three research, they determined the effects of site productivity and stocking on harvesting costs.

Effect of stocking on stand underbark volume

Effect of stocking on stand underbark volume at rotation at the eight stocking trials

The results confirm what would be expected from first principles, experience and the harvesting models used: that growth and yield will generally increase with stocking, at least within the range of about 300 to 1000 trees per hectare, and that unit-volume harvesting cost increases as average tree size decreases, either as a result of lower site quality/productivity or higher stocking. The analysis indicates the degree and variation of these responses and suggests that most of the Australian E. globulus estate might have been more profitably established at lower stockings than the stocking of 1200 trees per hectare that was commonly adopted in the 1990s. The effects of site quality and stocking on yield and tree size and thus harvesting costs, and harvest yield as a proportion of total stand underbark volume, as well as reduced growing costs at lower stockings, contribute to this conclusion.

Their report is confidential to CRC members, who can download it from the CRC members website.


Tom Baker
03 9250 6836