Scotland SUMMARY

Species mixtures, although promising for improving the growth of spruce on nitrogen-deficient sites, carry a risk of competition from the admixed nurse species. The mixture of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) planted at Gisburn Forest in 1955, in which nutritional benefits have been observed, provided a unique opportunity to study competition between these species. Pure plots of both species as well as the mixture were replicated in three blocks, allowing the effects of interplanting on the survival and mean diameter of each species to be tested statistically. Further, the grouped arrangement of the species in mixed plots presented a variety of competitive configurations between the two species. Instead of demonstrating the nursing benefit of pine to spruce, comparisons of mean diameters in pure and mixed stands indicated that spruce suffered and pine benefited from their interplanting at this site. Frequency distributions of tree diameters confirmed that spruce tended to be suppressed in mixture and pine dominant. Neighbour analysis revealed that spruce were significantly smaller when adjacent to pine and that this effect was mainly due to the larger size of pines. The increase