Ash dieback in the UK: A review of the ecological and conservation implications and potential management options

The death of native trees caused by non-native pathogens is a global problem. An assessment of the potential ecological and conservation impacts of any tree disease should identify: (1) ecosystem functions associated with the tree species; (2) which species use the tree and how; (3) the suitability of alternative tree species to replace the threatened tree species; and (4) potential management options to mitigate or reduce the impact of the disease.We assess the potential ecological impact of Hymenoscyphus pseudoalbidus (ash dieback) on Fraxinus excelsior in the UK. 953 species were identified as associated with F. excelsior trees: 12 birds, 28 mammals, 58 bryophytes, 68 fungi, 239 invertebrates, 548 lichens. Forty-four 'obligate' species were identified: 11 fungi, 29 invertebrates and 4 lichens; and 62 'highly associated' species.Off-setting the loss of ash with 'alternative tree species' may be one 'solution' to the biodiversity threat. No single alternative tree species can act as host for all ash-associated species but Quercus robur/. petraea can host 69%. In an assessment of ecosystem function, when compared to other European deciduous tree species, F. excelsior interacts with the environment in a unique way, particularly in relation to nutrient cycling.Exploration of different management scenarios in response to ash dieback indicated that management which did not remove infected F. excelsior trees was the best for 'obligate' and 'highly associated' species.The results highlight wide-ranging ecological implications of ash dieback of relevance to other invasive pests and pathogens that are threatening the integrity of other tree species and woodland ecosystems.