Breeding radiata pine for wood stiffness: review and analysis

Abstract

Summary Radiata pine is widely planted in the southern hemisphere, and has a versatile timber. The mature wood of this species is strong and stiff enough for a number of industrial uses, but current trends of harvesting at below 30 years result in a high proportion of low-stiffness juvenile wood. Radiata pine breeders have countered this reduction, indirectly, by selecting progenies for dense juvenile wood. However there is evidence now that improving juvenile wood density may not be sufficient to fully address low stiffness. This has led to work on assessing stiffness itself, and to studies on using microfibril angle in the tree improvement program. Progress on breeding radiata pine for stiffness in New Zealand is reviewed in this paper, with a briefer account of work in Australia. Several direct and indirect methods to improve stiffness arc described. These include static bending tests on boards and small clear specimens, acoustic and stress wave methods, and microfibril angle, in addition to density and pilodyn penetration. Two tools using acoustic/stress wave methods have been developed by the New Zealand forestry industry, and are being used operationally to segregate logs. A third tool (FAKOPP), developed in Hungary, shows promise for use on standing trees and hence could be suitable in screening progenies. SilviScan is an important Australian breakthrough and could potentially be used to predict longitudinal stiffness on hundreds of short samples per day. Combining acoustic/stress wave results with density and branch cluster frequency could well be a viable and cost—effective way to select progenies for clearwood stiffness in the juvenile wood zone. Information on stiffness could be combined with breeding values for growth rate, straightness and grain spirality to select parents for deployment and breeding.