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Assessing interactions between initial stand stocking and genotype on growth and form of year old <i>Pinus radiata</i> in Canterbury

Authors: Matthew J. Waghorn, Euan G. Mason, Michael S. Watt
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2007, Issue N.Z.J.For. 52(1) 2007, pp 24-30, May 2007
Publisher: New Zealand Institute of Forestry

Abstract: Influences of initial stand spacing and genotype on physical properties of 17-year-old Pinus radiata growing in a Nelder stocking design experiment in Canterbury were examined. Physical characteristics, including diameter at breast height, tree height, green crown height and stem slenderness were investigated for 385 trees, whilst internode length and branch index were examined for 65 trees. No significant interactions between breed and stocking were found, indicating that relatively simple adjustments to existing silvicultural models could represent impacts of stocking on a variety of tree breeds.

Diameter at breast height decreased from 41.1 cm to 17.7 cm as stand stocking increased from 209 stems ha-1 to 2551 stems ha-1. Green crown height increased from 1.8 m to 10.2 m with increasing stand stocking, whilst stem slenderness also increased with increasing stand stocking. Tree height was not significantly influenced by genotype. As expected the 870 long internode breed had significantly longer internode lengths than other breeds, demonstrating its defining physical characteristic.

Branch index (BIX) was significantly and positively correlated with tree diameter (r2= 0.80), with BIX ranging from 35 mm at 364 stems ha-1 to 13 mm at 2551 stems ha-1. After correction had been made for tree diameter, BIX exhibited a significant positive relationship with mean internode length which when included in the analysis increased the r2 from 0.80 to 0.90. Tree diameter and mean internode length accounted for the effects of stocking and genotype on BIX.

The results provide considerable insight into how stocking and genotype regulate stem geometry and as such provide managers with a demonstration of the effect of a wide range of operationally used stockings on these important external tree characteristics.
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