Genotype × site × silviculture interactions in radiata pine: knowledge, working hypotheses and pointers for research§

Favourable interactions between genotype, site and silviculture are desired for growing radiata pine, site and silviculture being two components of environment. Our challenge is to characterise the interactions so as to exploit them to advantage. Four classes of interaction are involved: three first-order interactions between pairs of factors; and one second-order interaction involving all three factors. Also of interest is to partition the interactions into two types: involving rank change of genotypes (RC interaction) and differing level of expression of genotypic differences among environments (LoE interaction). Tree breeders’ immediate concern is with main effects of environment and interaction effects on genotypes’ performance, yet prime interest for research and policy decisions lies in the role of environments and specific environmental factors in generating interactions. Of the two types of interaction, RC seems generally more important for breeding operations with LoE more so for deployment decisions. Existing information, and provisional expectations of interactions, is to be reviewed, mostly qualitatively, in terms of the comparative importance of RC and varying LoE. This will be done, for the first-order interactions, for various traits. Second-order interactions are as yet almost entirely conjectural. A framework is offered for accumulating both input from others and future research findings. In radiata pine, growth traits, especially stem diameter, tend to show marked RC interaction with site. Tree-form traits, however, seem mainly subject to LoE interaction, and disease resistance is intensely so. Among wood properties, some show very little interaction, while LoE interaction seems to occur for some other properties.