Skip to Content

Combating ash dieback – mitigating the impact of invasive diseases on biodiversity

Case Study 2019

Combating ash dieback – mitigating the impact of invasive diseases on biodiversity

Plant pests and diseases are not just problems for crops and horticulture. Plants that are central to our nature reserves, forestry systems, and urban environments can also suffer, bringing risks to biodiversity and ecosystem services. Improving resilience to pests and diseases, and increasing plant biosecurity, are therefore key actions for achieving healthy ecosystems.

JNCC works with a number of government bodies, non-government organisations and the community at large to help ensure that plant health issues are appropriately considered and prioritised, with a particular focus on biodiversity and ecosystem services. Thanks to our investments in data management and analysis, we can make rapid use of mapped and modelled biodiversity data to research and advise on the likely spread and impacts of specific non-native pests and diseases. Similarly, skills in evidence synthesis allow us to bring together and evaluate different sources of information to develop guidance and frameworks for helping to understand the options involved in mitigating impacts.

The future of the ash tree in the UK is currently threatened by an invasive fungal disease, Hymenoscyphus fraxineus (also known as ‘Chalara’) which causes ‘ash dieback’. The fungus blocks the water transport systems in trees causing leaf loss, lesions in the wood and on the bark, and the dieback of the crown of the tree; ultimately, it can lead to tree death or felling in the interests of public safety.

Following the detection of ash dieback within the UK in 2012, JNCC has been supporting Defra and the devolved administrations in developing an understanding of its likely impacts on biodiversity, how important these impacts are, and the means for monitoring and mitigating any biodiversity changes.


Understanding impacts and options

The widespread death or felling of ash trees within the UK has the potential to impact on populations of other plant and animal species that use ash trees for feeding, breeding or as a habitat. It was therefore important to develop a rapid understanding of the issue to enable the most effective responses to be identified.


JNCC has helped achieve this through:

  • gathering datasets and undertaking analysis to create a map providing evidence of the location of important ash trees and woodlands throughout the UK, as a required first step in understanding the possible spatial extent of the impact of ash dieback on UK biodiversity;
  • commissioning and managing research into the ecological impact of ash dieback on UK woodland habitat and ash-associated species and modelling the likely consequences of six different management scenarios;
  • describing possible options for mitigating impacts from ash dieback (including management, tree breeding, and replacing ash with other tree species) and evaluating these options based on biological evidence, views from forest managers, and previous experiences with resistant tree breeding in other countries;
  • investigating further tree species for their potential to host ash-associated species and researching the changes in ecology that would happen after the loss of ash if it was replaced by these tree species (whether as a result of natural colonisation or from management interventions);
  • developing a general framework to help decision-makers understand the stages involved in using tree breeding to produce resistance to specific tree pests and pathogens, as well as the different breeding options available and the potential risks and timescales.


The bigger picture

Our response to the ash dieback outbreak built on our previous work on the control of Phytophthora infections in bilberry (Phytophthora is a genus of plant-damaging water moulds that are responsible for a number of notorious plant diseases which have the potential to devastate heathland sites). Here we used our data and analysis to map and model the distribution of a range of different host species, and to assess the likely impacts.

There are many other pests and diseases that are threatening the health of UK trees. JNCC is maintaining its focus on evidence and advice to help ensure that plant health issues that impact trees, wild plants and their associated biodiversity are appropriately considered and prioritised. We work closely with a range of partners to ensure that biodiversity considerations are built into plant health responses, including developing understanding of the viability of different options and how these options relate to broader priorities emphasising ecosystem resilience.


Further information:

Woodcock, P., Cottrell J. E., Buggs R. J. A, Quine, C. P. 2018. Mitigating pest and pathogen impacts using resistant trees: a framework and overview to inform development and deployment in Europe and North America. Forestry: An International Journal of Forest Research, 91, Issue 1,

The Distribution of Important Ash in Great Britain

Mitchell, R.J., Bailey, S., Beaton, J.K., et al. 2014. The potential ecological impact of ash dieback in the UK. JNCC Report No. 483  

Chalara ash dieback (Hymenoscyphus fraxineus) on the Forest Research website


Team: Ecosystem Analysis

Back to top