The updated guidance, launched today (20 September) at the tree industries' APF Exhibition, suggests natural regeneration will be more likely to throw up tolerant or resistant individuals, while warning of the public risk from mature infected trees.
It urges woodland owners and managers to think strategically about the management of their ash trees and adopt best practice to help reduce the impact of the disease.
"The percentage of potentially tolerant trees is likely to be very low but with careful management these could regenerate and the species could continue to exist at low levels in mixed stands," the guidance states.
"Encouraging multiple opportunities for regeneration (through a larger number of smaller interventions for example) will increase genetic 'churn' and may result in more chances of tolerant trees emerging."
Ash cannot currently be planted due to import and movement controls on all Fraxinus species, it points out.
The updated guidance also highlights how to:
- conserve the environmental benefits of ash woodland through active woodland management including, for example, encouraging structural diversity or identifying tolerant trees;
- increase the resilience of woodlands by planting alternative species to ash, as well as developing stands of mixed species and age to help make woodland less vulnerable to disease;
- manage the health and safety risks caused by diseased trees.
On this last point, it warns: "After five years, about half of affected trees are likely to have sufficient decay to be assumed hazardous."
Forestry Commission director of forest services Richard Greenhous said: "The ash tree and the woodlands they inhabit are not going to disappear. Through updated guidance we hope to help landowners maintain the benefits of the ash tree in English woodlands, whilst mitigating the risks posed by ash dieback."
The updated guidance is in line with the Government’s Tree Health Resilience Strategy, launched in May, which called for landowners, charities, the public and government to work together to build resilience against pests and diseases to protect the nation’s trees.
Since 2012, when ash dieback was first confirmed in the UK, the Government has committed more than £37 million into tree health research, including research into the genetic component for tolerance to the disease.
Restoration grants for woodlands affected by ash dieback are available through the Countryside Stewardship scheme.
Separate advice on managing non-woodland ash will be published later this year.