Relationship between branch thickness and stand density in radiata pine.  L. A. Pederick and I. D. Abbott.  December 1985.  11 pp. (unpubl.)

SUMMARY

The effect of espacement on branch thickness in Pinus radiata was studied in a 13-year-old Nelder trial (a spacing trial established according to a variable density design, with trees arranged along radii in concentric circles at increasing distances from the centre) in the Warrenbayne Plantation. The approximate square spacings represented by trees in the trial were 1.5 m, 1.9 m, 2.3 m, 2.9 m, 3.5 m and 4.3 m. The overbark diameter of all branches on that portion of the tree stems from 2.9-4.7 m above ground level was measured and converted to underbark diameter by a function calculated from representative samples of measurements of branch diameter and bark thickness.

Main stem diameters of the trees ranged from 15.7 cm at 1.5 m spacing to 29.7 cm at 4.3 m spacing. Average branch diameter (underbark) also varied directly with spacing (and with tree diameter) from 1.35 cm at 1.5 m spacing to 2.52 cm at 4.3 m. The proportion of branches with underbark diameter exceeding 3.0 cm, an arbitrary limit chosen to indicate larger knot size, in sawn timber increased from 2% at 1.5 m to 37% at 4.3 m. The number of branches per metre of stem did not vary significantly with tree spacing.

For 2.4 m and 3.0 m, the spacings currently used in practice, mean branch diameter was calculated to be 1.67 cm and 1.98 cm respectively, and the proportion of branches exceeding 3.0 cm diameter was 12% and 19% respectively.

The plants in the Nelder trial were genetically improved families, and some evidence that their branch thickness was less than that of unimproved trees in routine plantings was found. Therefore, it appears that in terms of average branch thickness the use of trees of seed orchard origin will partly compensate for the increase which will occur wherever planting espacement is increased from 2.4 m to 3.0 m.