This paper presents an abridged account of a study by the author in 1978, which is intended to develop the understanding of spatial variations in the growth of trees and refinement of the analytical techniques used. The results of the yield analysis at the national level are applied on a compartment basis in two study forests in England and Wales. The purposes of the analyses is to obtain a more precise knowledge of the locations that produce high and low yields for each species; also to ascertain how far this information either confirms or contradicts site selection by means of the 'conventional guidelines' published in Forestry Practice, Forestry Commission, 1978. An attempt is made to indicate, in a preliminary way, how locational changes in the planting of species for the next rotation can give higher yields per unit of forested area.