How local is local? Identifying the scale of adaptive variation in ash (Fraxinus excelsior L.): results from the nursery

Local genotypes may be well adapted to local conditions and are seen by policy makers as desirable for both conservation and genetic improvement. Existing provenance trials show adaptation of British material to British conditions, whereas material from continental Europe often suffers from the late spring frosts typical of the British climate. However, little is known about the extent of adaptive variation within Britain, so discussion about suitable local seed sources lacks sound evidence for the scale over which adaptation occurs. Additionally, the current shift towards planting and managing woodlands for conservation or environmental benefits requires trees with good reproductive vigour, seed and seedling survival, the ability to compete with other species and adaptive capacity in the face of long-term change. Germplasm selected in production forestry plantations for growth, form and other commercial criteria may not be so well-suited to survival in the more competitive environment of semi-natural mixed woodland. This paper introduces the background to these issues and reports initial results from a reciprocal transplant experiment established among eight autochthonous common ash (Fraxinus excelsior L.) populations, covering a hierarchy of scales (geographical and environmental) over the species' range within England and Wales. Nursery data shows no evidence of home site advantage, with the same best performers growing well on most soils.