Question to the Department for Environment, Food and Rural Affairs:

To ask the Secretary of State for Environment, Food and Rural Affairs, what recent assessment her Department has made of the (a) current and (b) future (i) prevalence and (ii) impact of ash dieback.

Ash dieback is a fungal disease of ash trees that was first detected in Great Britain in 2012. It can be spread by infected planting material but is also capable of spreading naturally up to 75km through airborne spores. The disease is now present in all counties, but levels of infection differ at a local level. The impact of the disease varies by tree age, provenance, climate and site factors such as soil type and the presence of secondary pathogens like honey fungus. The disease progresses more quickly in young or stressed trees in ash dominated woodlands, and mortality rates of up to 85% have been recorded in some plantations. Fewer symptoms are observed on ash trees growing in open spaces.

There are an estimated 125 million ash trees in UK woodlands and up to 60 million ash trees outside of woodlands. 1-5% of these trees will be naturally tolerant to the disease and the Government planted the UK’s first archive of 3000 tolerant ash trees in 2020, raising the possibility of a future breeding programme for tolerant ash. Local effects on landscapes will be gradual, and tolerant trees and other tree species are expected to naturally repopulate sites and replace susceptible trees over time. The total cost of ash dieback to the UK has been estimated at £14.6 billion over the next 100 years, based on the cost of dealing with the immediate impacts of the disease, replanting and the future loss of ecosystem services.