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Common ash (Fraxinus excelsior L.) is an important timber species that is widespread in broadleaved woodlands across Europe, where it is currently declining due to the fungal pathogen (Hymenoscyphus fraxineus (T. Kowal) Baral et al., 2014) causing ash dieback. Using the UK as our case study, we assess: (1) likely woodland composition following ash dieback and (2) choice of replacement species for production planting. The greatest impacts on woodland composition will occur where ash forms a larger proportion of the canopy. In such woodlands, larger gaps formed from the loss of ash, are likely to be filled by sycamore (Acer pseudoplatanus L.) and beech (Fagus sylvatica L.) under current climatic conditions and where there is little management intervention. Native woodland policy regarding sycamore and beech may need to be reviewed in UKdesignated woodlands where these species are considered non-native. For actively managed production woodlands, 27 replacement tree species for ash are considered, some of these are non-native and present options for continuing production forestry objectives on former ash sites. An assessment of replacement species shows there is no single species that can substitute for the wide range of site conditions associated with the good growth of ash. In deciding to replace ash with another tree species, the decision on selection should be made based on particular site conditions and woodland objectives.

This collaborative investigation was aimed at using morphological and molecular characters to study inter-and intraspecific variation within isolates of Glomus mosseae and Glomus coronatum from different parts of the world, A secondary aim was to assess whether any divergence found was genetically based and/or correlated with the biogeographic origin of isolates. Morphological evaluations of various possible taxonomic characters including spore colour, size, sporocarp architecture and hyphal attachment morphology, showed that only spore colour couid discriminate the two groups, Isozyme analysis of malate dehydrogenase and esterase loci clearly confirmed this grouping of the two species complexes, SDS profiles and cluster analysis showed the same separation on a selection of isolates from the two groups, A comparison of a representative isolate from the G, coronatum group (BEG 49) wrth other arbuscular mycorrhizal fungi using G, mo^^eae-specific primers also provided evidence for separation of the two species complexes. The data and methodology employed provide a blueprint for future multimodal and niultidisciplinary approaches to the unravelling of taxonomic problems within this ancient group of symbiotic fungi.

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