Top-pruning in the Korweinguboora Pinus radiata seed orchard.  L.A. Pederick.  March 1972.  9 pp. (unpubl.)

SUMMARY

Top-pruning of young P. radiata ramets (grafts), by cutting back their leading stems, was undertaken in order to increase flowering capacity by stimulating branch development. Four years after the treatment in January 1968 the plants have made considerable growth and, but for one clone, AV22, there has been no increase in flowering as a result of top-pruning.

Increased flowering as a result of the top-pruning, was recorded 2 years after the treatment, (but only with clones WA2, NR12, CA4, CR54 and AV22). This response was not sustained in the following years, except for AV22.

Following an additional light top-pruning in January 1970 reduced flowering was recorded the following year, and also a lower proportion of strobili I developed to the yearling cone stage. A physiological shock seems to have been induced.

AS a consequence of the early top-pruning treatment ramets have made less height growth with more strongly developed and longer branches. Cone collections will be cheaper for a number of years. Top-pruning at an early age incurs an insignificant sacrifice of flowering, and appears to have some desirable effects, though no effect on ultimate yields.

Some top-pruned ramets tend to develop a multi-stemmed habit which could cause problems for future cone collection due to stem instability. One central vertical stem is most desirable. This can be ensured by a follow-up operation 12 months later to prune back competing leaders.

It is recommended that ramets be top-pruned when they first attain a height of about 8 feet, provided there is a follow-up treatment of competing leaders the following year. Pruning of large ramets is not recommended at the present stage due to sacrifice of cones and costs of treatment. Experimental work with larger trees is required.