Sixth year results from four ash (Fraxinus excelsior) breeding seedling orchards

A series of four ash (Fraxinus excelsior) progeny trials were established a s Breeding Seedling Orchards (BSOs) in 1993. The aim was to improve the for m and vigour of Britain's second most widely planted broadleaved species. F our sites were planted, employing seed from 36 selected mother trees across Great Britain. By 1998 the average height of the trees in the best family, on the best site, was 2.7 m. Tree heights were first measured in 1996 and determined to be highly heritable. In July 1998 they were assessed for dbh, height, forking, straightness and branching. Analysis confirmed that heigh t growth is strongly heritable with estimates of genetic gain from 2% to 25 %. Heritability for height does not appear to be declining and comparisons with 1996 family rankings reveal a very strong consistency at all sites. Th ese results suggest that juvenile - mature correlations may be strong in as h. The extent of branching is strongly heritable, although heritabilities f or forking and straightness were much weaker.