JNCC Report No. 483 The potential ecological impact of ash dieback in the UK Mitchell, R.J., Bailey, S., Beaton, J.K., Bellamy, P.E., Brooker, R.W., Broome, A., Chetcuti, J., Eaton, S., Ellis, C.J., Farren, J., Gimona, A., Goldberg, E., Hall, J., Harmer, R., Hester, A.J., Hewison, R.L., Hodgetts, N.G., Hooper, R.J., Howe, L., Iason, G.R., Kerr, G., Littlewood, N.A., Morgan, V., Newey, S., Potts, J.M., Pozsgai, G., Ray, D., Sim, D.A., Stockan, J.A., Taylor, A.F.S. & Woodward, S. January 2014 © JNCC, Peterborough 2014 ISSN 0963 8091 For further information please contact: Joint Nature Conservation Committee Monkstone House City Road Peterborough PE1 1JY www.jncc.defra.gov.uk This report should be cited as: Mitchell, R.J., Bailey, S., Beaton, J.K., Bellamy, P.E., Brooker, R.W., Broome, A., Chetcuti, J., Eaton, S., Ellis, C.J., Farren, J., Gimona, A., Goldberg, E., Hall, J., Harmer, R., Hester, A.J., Hewison, R.L., Hodgetts, N.G., Hooper, R.J., Howe, L., Iason, G.R., Kerr, G., Littlewood, N.A., Morgan, V., Newey, S., Potts, J.M., Pozsgai, G., Ray, D., Sim, D.A., Stockan, J.A., Taylor, A.F.S. & Woodward, S. 2014. The potential ecological impact of ash dieback in the UK. JNCC Report No. 483 Acknowledgements: We thank Keith Kirby for his valuable comments on vegetation change associated with ash dieback. For assistance, advice and comments on the invertebrate species involved in this review we would like to thank Richard Askew, John Badmin, Tristan Bantock, Joseph Botting, Sally Lucker, Chris Malumphy, Bernard Nau, Colin Plant, Mark Shaw, Alan Stewart and Alan Stubbs. Chris Preston kindly allowed us access to the electronic data from New Atlas of the British and Irish Flora, and IFOS (Forestry Commission) kindly provided sample square summary data from the National Forest Inventory. We thank David Boshier, Peter Buckley and Keith Kirby for peer reviewing the report. The James Hutton Institute led the project and was the main author of Chapters 1, 3, 4, 5, 9, 10, 12, 13 and 15, with species experts from other organisations producing chapters on lichens (Royal Botanic Garden Edinburgh), bryophytes (Independent Consultant), fungi (University of Aberdeen and the James Hutton Institute), and birds (RSPB). Forest Research was the main author of Chapters 2, 14 and 16. Biomathematics and Statistics Scotland provided statistical support for Chapters 12 and 15. All other chapters were produced jointly. The funding bodies were represented by members of the Steering Group: JNCC (V. Morgan), Forestry Commission (S. Bailey), Natural England (E. Goldberg), Scottish Natural Heritage (J. Hall), Natural Resources Wales (L. Howe) and Northern Ireland Environment Agency (J. Farren). Authors’ Organisations are as follows: Beaton, J.K., Brooker, R.W., Gimona, A., Hester, A.J., Hewison, R.L., Hooper, R.J., Iason, G.R., Littlewood, N.A., Mitchell, R.J., Newey, S., Pozsgai, G., Sim, D.A, Stockan, J.A., and Taylor, A.F.S. The James Hutton Institute, Craigiebuckler, Aberdeen, AB14 8QH. Bailey, S. Forestry Commission, Silvan House, 231 Corstorphine Road, Edinburgh, EH12 7AT. Bellamy, P.E. The Royal Society for the Protection of Birds, The Lodge, Sandy, Bedfordshire, SG19 2DL. Broome, A., Chetcuti, J., and Ray, D. Forest Research, Northern Research Station, Roslin, Midlothian, EH25 9SY. Eaton, S., and Ellis, C.J. Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh, EH3 5LR. Farren, J. Biodiversity Unit, Northern Ireland Environment Agency – Natural Heritage, Klondyke Building, Cromac Place, Belfast, BT7 2JA. Goldberg, E. Natural England, Unex House, Bourges Boulevard, Peterborough, PE1 1NG. Hall, J. Scottish Natural Heritage, Great Glen House, Leachkin Road, Inverness, IV3 8NW. Harmer, R., and Kerr, G. Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH. Hodgetts, N.G. Bryophyte Consultant, Cuillin Views, 15 Earlish, Portree, Isle of Skye, IV51 9XL. Howe, L. Natural Resources Wales, Maes Y Ffynnon, Penrhos Road, Bangor, Gwynedd, LL57 2DW. Morgan, V. JNCC, Monkstone House, City Road, Peterborough, Cambridgeshire, PE1 1JY. Potts, J.M. Biomathematics and Statistics Scotland, Craigiebuckler, Aberdeen, AB15 8QH. Woodward, S. University of Aberdeen, Institute of Biological and Environmental Sciences, Department of Plant and Soil Sciences, Cruickshank Building, St. Machar Drive, Aberdeen, AB24 3UU. 1 Summary Introduction 1. Ash is a common woodland, hedgerow, park and garden tree throughout the UK. The arrival of the disease ash dieback within the UK may result in the death of a large proportion of British ash trees. (Confidence: Medium). 2. If ash dieback does lead to widespread death of ash trees within the UK, it is likely that there will be a high negative impact on populations of plant and animal species that use ash trees for feeding/breeding or as a habitat (e.g. epiphytic lichens, bryophytes, specialist invertebrates). (Confidence: High). 3. When assessing the potential impact of ash dieback on biodiversity, a worst case scenario (more than 95% of ash eventually dying) has been taken throughout this report. The actual impact will depend on the extent and severity of the disease in the UK (which is unknown at this time), and whether or not resistant ash populations are identified. Objectives of the research project 4. The objectives of the research project were: • to collate information about the ecology of ash and species which use ash and how they do so; • to assess how British woodlands might change as a result of the loss of ash; • to define a range of management scenarios which might be applied as a result of ash dieback, and to assess how these might affect species that currently use ash and the general composition of ash-related woodland habitats. 5. The research focused on potential implications of ash dieback and did not include consideration of other pressures such as pollution or climate change that may also cause changes in woodland structure and communities. 6. The research focused on potential impacts on ash associated species and on the ecology of ash woodlands, but did not provide a detailed assessment of the potential impacts of ash dieback on the delivery of ecosystem services, which would be an important consideration in future research and management decisions. Ecology of ash 7. Ash lies at the extreme of the range of UK tree species in that it produces nutrient-rich highly degradable litter that does not form a deep litter layer and which maintains a high soil pH. Since the litter breaks down so rapidly, little soil carbon is sequestered, and the rates of nutrient turnover around ash trees are high. The tree species that may replace ash if ash dieback-related mortality is high may not preserve these ecosystem characteristics. The nutrient cycling characteristics of ash and the high light penetration 1 For all statements in the summary (except those that are methodological) an indication of the confidence of the statement is provided. Where the statement is based on evidence from a literature review confidence levels are provided using the LWEC reporting card method of high, medium or low http://www.lwec.org.uk/sites/default/files/attachments_report_cards/Water_report_card_web.pdf. Where evidence is based on data an indication of strength of this data is provided e.g. percentage of records in the database. through the leaves also contribute to the diversity of the associated ground flora. (Confidence: High). 8. The species composition of the soil decomposer community, from bacteria through to soil macro-invertebrates, and of the associated arbuscula mycorrhizal fungi, is of considerable functional significance for ash, shaping its ecosystem functions, and the biodiversity of the other associated assemblages. (Confidence: High). 9. Ash is commonest in mixed woodlands, rather than as a sole canopy dominant. Its saplings are shade-tolerant, enabling it to respond well to fill any new canopy gaps. (Confidence: High). 10. The current structure of ash woodlands was assessed using the National Forest Inventory (NFI) which includes survey data from 15,000 one-hectare sample squares randomly located across Great Britain. The total area of ash, the area of ash as a percentage of total woodland, standing volume and number of ash trees all follow a similar pattern, being lowest in Scotland, and lower in the NFI Region of northern England than in Wales and the more southerly areas of England. Overall, from the available data, there appears to be little difference between regions in the age-structure of ash-related stands, with most ash trees being of young to moderate age (11–60 years old) and of small diameter (<20cm), with relatively few large old ash trees present in woodlands in the UK. The Northern Ireland register of woodland suggests that the area of ash as a percentage of total woodland in Northern Ireland is similar to the NFI Regions of northern England and southern Scotland.(Confidence: High). 11. The UK was divided for the purpose of this project into five ‘ash-relevant’ regions, based on the amount of ash present. These regions were further sub-divided on the basis of climate and soils to produce a total of nine ash-relevant sub-regions within which the impacts of ash dieback and the potential effects of different management scenarios were assessed. Species using ash 12. In total, 1,058 species were identified as being associated with ash (ash-associated species): 12 birds, 55 mammals, 78 vascular plants, 58 bryophytes, 68 fungi, 239 invertebrates, and 548 lichens. Of the 55 mammals, 28 use the ash trees and the remainder use the ash woodland habitat; the vascular plants use the ash woodland habitat rather than the trees themselves. All other species groups have been limited to those which use the ash trees themselves for the purposes of this review.