Fragixen Ash for the future: defining diverse and robust European ash populations for conservation and regeneration

The FRAXIGEN project is exploring patterns of genetic variation, and the biological and ecological forces shaping them, in three European Fraxinus (ash) species in six countries across their native ranges. There has been a shift in forest policy across much of Europe towards an emphasis on conservation objectives, in which considerations of sustainability, ecological restoration, biodiversity conservation, enhancement of cultural heritage and landscape character are key elements. Trees grown in this context must be able to succeed within complex woodland ecosystems, requiring qualities such as reproductive vigour, seed and seedling survival, adaptive capacity for extreme environments and ability to compete with other species. This contrasts with planting for conventional production objectives, with open, clean-weeded plantations in which environmental stresses are minimised. So far, the only criterion widely applied to the seed selection for conservation planting is that it should be locally sourced, but there has been so selection for these competitive traits. Moreover, we have lacked the basic knowledge about patterns of genetic diversity, both within and between populations that would allow us to select diverse material which would be robust and adaptable to complex environments and environmental change.

In FRAXIGEN we are looking at the scale over which local adaptation takes place, by planting series of trials (in Britain and Greece, for northern and southern Fraxinus species) in which seed and seedlings from eight different woodlands, situated at distances ranging from less than ten to several hundred kilometres, are planted within the same eight woods. We are also estimating how genetically diverse each population is, using molecular methods. By comparing survival and early growth of local and distant seed sources, we will see how important local origin really is in seed source selection, or whether competitive success in a woodland setting is related more to other qualities such as genetic diversity. This will provide an important new scientific basis for the (currently sometimes arbitrary) definition of local seed zones.

Once an appropriate seed source has been chosen with the help of these criteria, we also need to know which, and how many, trees to include in a seed collection. The reproductive biology of Fraxinus is complex, with three genders (male, hermaphrodite and female, as well as intermediate forms) occurring in different combinations in the three species. In FRAXIGEN we are looking in detail at the relative success of seed from controlled pollinations between the different gender combinations, whether hermaphrodite trees produce self-pollinated seed, and if so whether this performs less well because of inbreeding. This knowledge will have important implications in selecting the trees from which seed should be collected.

In the restoration of native woodlands, the use of genetically diverse, resilient and locally-adapted seed is an essential part of the development of a functional, sustainable and biodiverse ecosystem. For the first time, FRAXIGEN will provide a sound scientific basis on which to choose such material.

Further information:

Fraxigen project.