Britain's considerable potential for the fast growth of forest crops is due to four main advantages: climate, arboricultural experience, seed provenance research and management practices. In addition to these there is a fifth dimension which is revealed by a spatial interpretation of yield variations, and it is the purpose of this paper to analyse yield variations in Forestry Commission plantations in England and Wales through the application of computer mapping and recommendation techniques. Maps of yields show distinct clines of growth rates which are consistently higher, irrespective of species, in the south and west than in the north and north-east of the country. The locational coincidence of high and low yielding forest areas with macro factors such as mean annual rainfall and accumulated temperature suggest a strong climatic influence in yield variations, and provide more quantitative thresholds governing species and site selection than were previously available. Finally, through the use of a recommendation technique attempts are made to show how it should be possible to increase forest productivity without incurring an increase in forest land.