13 November 2012
Find out everything you need to know about ash die-back and how it might affect nature in the UK.
What is 'ash die-back'?
Ash die-back is a disease that has caused widespread damage to ash trees across Europe. The disease is caused by a fungus which occurs in two named forms. Chalara fraxinea causes the symptoms of the disease in infected ash trees while its other form, Hymenoscyphus pseudoalbidus, grows as small mushroom-like fruiting bodies in infected leaf litter and helps spread the disease.
It's one of a number of new fungal diseases that are causing serious problems in our wildlife (including amphibians, bats and other trees), due to the movement (both deliberate and accidental) of living things between countries and regions.
What species does it affect?
Ash die-back most commonly affects the common ash but has also been recorded in other ash species. But it doesn't affect rowan (also known as the mountain ash), which belongs to a different tree genus. It can infect ash trees of all ages, but is most frequently recorded in younger trees. They appear to be more susceptible to the disease -succumbing within a year or two of symptoms appearing. Mature trees are able to resist for longer, though some may succumb after repeated infections.
Where did it come from?
Ash die-back was first recorded in Poland in the 1990s from where it has rapidly spread north and west across Europe.
The disease was first reported in the UK in a plant nursery in February 2012, in a consignment of ash trees imported from the Netherlands. Subsequent checks revealed a number of other infections, mostly among nursery imports but also in a number of newly-planted sites.
In October 2012 the Forestry Commission announced the first confirmed cases of the disease in mature ash trees not associated with any new planting.
Up-to-date maps of the spread of the disease can be found on the Forestry Commission website.
How does it spread?
The disease spreads via fungal spores. Infections begin on the living leaf stalks and spread through the tree.
Spores which can spread the infection are produced by the small mushroom-like fruiting bodies that grow in the infected leaf litter during June to October. These fruiting bodies can also occasionally be seen on dead twigs and infected shoots still attached to live trees.
There has been much emphasis placed recently on the spread of this disease on the wind. While it is true that this is the way that the disease spreads naturally, it is also clear from the quick spread of the disease across Europe that wind is not the only answer.
Initial movements (both deliberate and accidental) of infected plant material between countries (e.g. from the importation of infected plants to nurseries) are likely to have contributed greatly to the rapid spread of this disease.
There is no evidence to date to suggest that birds or animals are assisting the spread of this disease.
How can the spread of this disease be stopped?
It is looking increasingly likely that we will not be able to eradicate this disease from the UK. So the next stage is to limit the spread of the disease by removing selected diseased trees and taking care not to spread the disease (improved biosecurity).
Young trees are the most susceptible and often die within a year or two of becoming infected, so they will be identified and destroyed. Older, more mature trees are able to resist the disease for longer and will not be destroyed.
Unfortunately, there is currently no known cure for this disease. Research in Europe has shown that some ash trees are more resistant to the disease than others, and that there is some degree of natural resistance. Work is now underway in the UK to identify those trees with the highest degrees of resistance to help generate replacement stock, should trees be lost.
On 29 October 2012 the UK Government also introduced new legislation to ban the import of ash plants, trees and seeds. The legislation also bans the movements of ash trees and seeds within the UK.
What is the RSPB doing on its nature reserves?
We are surveying our reserves for signs of the disease, particularly among young ash trees. We are also asking our staff to follow the same simple biosecurity guidelines outlined above.
What could ash die-back mean for the UK's wildlife?
Ash trees are an important part of our native woodlands and hedgerows. Some 13 per cent of the trees in broadleaved woodland are ashes
They are hosts to a wide range of species, but are particularly important for fungi, invertebrates which live in dead wood, some lichens and other plants. Large, mature trees, with their assorted cracks and hollows, also provide valuable nesting sites for many woodland birds as well as roosting sites for bats. Woodlands with lots of ash trees are also rich in native wildflowers.
It is very difficult at this stage to predict what impact this disease will have on the wooded landscape of the UK. Ash-dominated woodlands are relatively small in number but rich in species and so the loss of large numbers of ash trees in such locations is likely to have a significant impact.
However, not many species are reliant entirely on ash trees, so away from dominant stands the impact may be lessened. There may also be beneficial changes in the structure of some woodlands while the production of increased volumes and diversity of 'dead-wood' habitats is also likely to benefit wildlife which makes use of dead wood.