On poor soils in Australia the growth response of both eucalypts and pines is very great indeed where stock is planted on ash beds. The ash bed response can be duplicated by dry-heating soil in an electric oven to about 150°C. It can also be equalled by luxury doses of N and P. Nevertheless the precise mechanisms of response no doubt involve many factors and it is likely that there is a microbiological component. Full understanding of the phenomenon is likely to have a marked bearing on plantation practice on poor sites.