Potential for the improvement of silver birch (Betula pendula Roth.) in Scotland

Summary Despite the increasing use of silver birch in Scottish forestry there has been no consistent attempt to investigate the possibility of improving the productivity and quality of the species through a breeding programme. This paper analyses the results, at 12 years, of the only progeny trial in Britain, established near Banchory, Aberdeenshire. Based on ‘plus-tree’ selections, 14 full-sib and 10 half-sib families were established in a randomized block design. Significant differences among families were found for height, diameter, stem form and forking habit and a multi-trait index designed to emphasize desirable economic traits. Phenotypic correlations between traits were positive and significant. Estimated heritabilities (family) in the half-sib and full-sib families were similar and greatest for height (h 2 ~0.6) while the mean stem form of the half-sib entries which had been selected for stem quality was 14 per cent greater than those selected for vigour alone. General combining ability estimated from the controlled pollinations was only significant for height and specific combining abilities were negligible. The full-sib families were, however, superior to the half-sib generally and the five outstanding entries were derived from crosses among only four parents, which have origins spread over 10° of latitude. After thinning, the trial matches published management table values equivalent to Yield Class 10 (max m.a.i. m 3 ha ‐1 per year) and a target diameter of 30 cm at 30 years is likely to be achieved. This level of production, combined with high stem quality, if attainable generally, would transform the economic outlook for this species in Scotland. It is concluded that this trial demonstrates the potential for improving the performance of the species. Selection of adapted ‘plus-trees’ on a regional basis, for inclusion in polyhouse breeding orchards, is proposed, so as to rapidly yield improved seed.