Sitka spruce, Picea sitchensis (Bong.), Carr, has attained a a position in British forestry unrivalled by any other exotic species and as a consequence has been planted on an increasingly wider range of sites. However, where Calluna vulgaris is a major component of the vegetation young spruce trees often show the condition known as 'check' in which growth is slow and the foliage short and yellow. Various techniques for alleviating this condition have been tried with some success but the mechanism of 'check' remains unknown at present. In Durris Forest, Aberdeenshire, Calluna heathland inter-spersed with grassy flushes is planted with young Sitka spruce which show considerable variation in growth from healthy to the 'checked' condition. Experimental plots were established on 8 sites differ-ing in elevation and vegetation and studies were made of the sites and the trees growing upon them. The results suggest that exposure to wind depresses the growth of young trees more strongly than had been previously realised. The species composition of the vegetation was found to be a useful indicator of the future growth of young Sitka spruce. Growth was poorer on sites dominated by Calluna where the peat was found to be lower in nitrogen, phosphorus and potassium, had a higher moisture content, lower air content and greater depth than that obtained from comparable sites dominated by grasses where tree growth was consistently better. At a given elevation and aspect the differ-ences and similarities in dry matter production of the trees could be satisfactorily explained by careful assessment of the compo-sition of the vegetation.