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

FRAXIGEN, a research project funded under the EU 5th framework programme, has been underway for the last three years in six European countries to improve our understanding of the genetic resources of the three principal native Fraxinus species of Europe: F. excelsior, F. angustifolia and F. ornus. The FRAXIGEN project (EU contract no. EVK2-CT-2001-00108) has ten partners in Greece, Romania, Slovakia, Spain, Sweden and the United Kingdom carrying out parallel studies on the three species in different areas of their natural distribution.

The project addresses three central issues:

• Understanding population genetic structure and dynamics and the forces shaping them;

• Assessing the importance and scale of local adaptation;

• Guidance on selection of genetically appropriate planting material for maintenance of diversity and sustainability.

The first issue has been addressed through a combination of laboratory-based studies of neutral molecular variation and field-based research, which has investigated the complex reproductive biology of the three species. Firstly, nuclear microsatellite markers were used to estimate genetic diversity within populations, and the extent of differentiation between them, for 15 F. excelsior populations in the UK and Scandinavia, and for 30 populations each of F. angustifolia and F. ornus in the Mediterranean and across Central and southeastern Europe. For the same populations, plus some additional ones, haplotypes were also characterised using chloroplast microsatellites, to increase existing information (from previous research) on post-glacial colonization routes of the three species. In addition, the same nuclear markers were used for detailed studies of within-population genetic structure, gene flow and mating system in 2-3 populations of each species.

These molecular studies have been complemented by phenological observations and controlled pollination experiments to investigate each species’ potential for self-fertilization, as well as the success of different genders as pollen parents (males vs. hermaphrodites in F. excelsior and F. ornus) and seed parents (hermaphrodites vs. females in F. excelsior). Together, these field studies are helping us to interpret the findings of the molecular studies of mating system and gene flow.

The second major component of FRAXIGEN concerns the scale over which localized adaptation occurs in Fraxinus: this has direct relevance to the issue of defining ‘local’ seed sources, in accordance with the Helsinki Guidelines developed by the second Ministerial Conference on the Protection of Forests in Europe (MCPFE, 1993), which state that “local provenances should be preferred where appropriate”. However, there has been little scientific evidence on which to base the designation of seed collection zones for Fraxinus.

In FRAXIGEN, a reciprocal transplant experiment (RTE) has been set up at eight sites for each species (in UK for F. excelsior, in Greece for F. angustifolia and F. ornus) to investigate this issue. Seedlings were raised from seed collected at the eight autochthonous stands, chosen to be at varying distances apart, and these eight provenances were planted together in trials at the same eight sites, so that at each site one ‘home’ population is compared with the other seven ‘away’ populations. The trials have been planted within the woodlands, fenced but with minimal site preparation or weeding, so that the plants are subjected to similar competitive pressures to those they would encounter under conditions of natural regeneration. This approach has been taken because the directives on local seed sourcing relate to planting for conservation and ecological objectives rather than production, so it is important to understand local adaptation in this context.

The project is due to end in June 2005 and it is now in the processing of translating its findings into practical guidelines. An international meeting organized by the project in Valencia, Spain, in April 2005, brought together policy-makers and scientists from 17 European countries to help the project team in this process. A short book summarising the FRAXIGEN project findings and recommendations will be published for practitioners and policy-makers. Further information is available from the Project Coordinator, Janet Stewart (email: janet.stewart_at_plants.ox.ac.uk) or from www.fraxigen.net