Ash Dieback — What it is, and the consequences for UK Woodlands
Eighty million Ash trees are expected to die in the UK due to the Ash Dieback fungus, representing a significant shock to the UK's natural environment. This article explores what this disease is, where it came from, and what the future looks like for UK Ash and the ecosystems they support.
What is Ash Dieback?
Ash Dieback is a fungus originating in Asia. Ash species found in Asia have developed a tolerance to the fungus and can weather its presence. However, this is not the case for European species of Ash.
The fungus landed in Europe about 30 years ago, and wreaked havoc as European Ash species have not evolved to have any defence against the fungus.
Ash Dieback fungus penetrates the Ash, growing inside of it. Eventually, the fungus blocks the tree's water transport systems which causes the tree to die.
Young Ash trees have less resistance to fight back against the fungus. Infection in young trees is likely to lead to death within ten years. More mature trees can sustain longer but become more prone to other infections because of a depreciated energy supply.
The first recordings of Ash Dieback in the UK were in 2012. Infected Ash trees were imported to a tree nursery from Europe.
Symptoms of infected trees are:
Leaves develop dark patches in the summer.
They then wilt and discolour to black. Leaves might shed early.
Dieback of the shoots and leaves is visible in the summer.
Lesions develop where branches meet the trunk. These are often diamond-shaped and dark brown.
Inner bark looks brownish-grey under the lesions.
New growth from previously dormant buds further down the trunk. This is known as epicormic growth and is a common response to stress in trees.
How big of a problem is Ash Dieback?
Ash is the third most common broadleaved tree species in the UK. Woodland Ash trees cover over 140,000 hectares of land in the UK. This is so much land it’s tricky to think of an analogy to help convey the scale — It's not helpful to say that it's the equivalent of 345,947 football pitches!
The potential damage gets even more mind-boggling when zooming out to the rest of Europe. Ash Dieback has been discovered in Ash trees in 21 countries. Denmark has reported that 90% of its Ash trees are infected with Dieback.
Environmental damage due to Ash Dieback
The lack of natural defence in Ash trees in the UK means that a lot of trees will become infected. Estimates range from 80-95% of all Ash trees in the UK will die, which is around 80 million trees.
Trees are communities supporting insects, smaller plants, and animals. What happens to the community without a community centre (i.e. the Ash tree)? Ash is the sole foodplant for at least 27 species of invertebrate. Ash has many associated species, such as orchids. Suffice to say, the loss of Ash will be devastating to the UK's ecological fabric.
The economic cost of Ash Dieback
How much will dealing with Ash Dieback cost the UK? Reportedly, around £15 billion! Why so much? For a few reasons — Ash Dieback poses a public risk, so it's up to the government to manage that risk and prevent damage.
One of Dieback's symptoms is that the wood's integrity weakens, causing Ash to fall. Up to 80 million trees falling without warning will have fatal consequences and damage personal and public property.
Ash also has commercial value. It's nicknamed "golden oak" and is often used as a replacement for oak. The Ash planted in the UK for commercial purposes won't be able to be harvested and processed. Also, it can't be shipped abroad. Ash Dieback represents a total loss.
What's the solution to Ash Dieback?
Sadly, Ash Dieback has no known efficient prevention or curative treatment. And so, the best that can be done is palliative care for our Ash population and their associated ecosystems.
Stemming the importation of infected trees
When first discovered in the UK in 2012, Ash tree importation was banned, preventing more infected trees from being planted in the UK and speeding up the demise of the UK's Ash population. Taking further action, the government has banned shipping Ash trees within the UK.
Let nature take its course
Right now, the UK will have to fight Ash Dieback through attrition. Ash trees will have to die, be removed along with fungal infections and spores, and be replaced with other species. Currently Hornbeam is one of the more popular replacements, due to its tolerance to harsher climates brought by climate change. Of course, this approach is a years-in-the-making one that won't see a recovery in UK woodlands for decades. And, with the accelerating dangers of climate change and the UK's goal to scale up woodland coverage, it's hard not to be sceptical of this approach.
Let science provide a solution
Some Ash trees are proving hardier than others. Scientists are seeking to identify genetic traits leading to their ability to fight or live with the disease. Identifying a tree's ability to withstand the disease, scientists are looking at either breeding programmes or genetic modification to replace Ash populations in the UK.
What you can do to fight Ash Dieback
The Forest Research has a map showing where at least one case of Ash Dieback has been confirmed. The map is updated four times a year.
Signs and symptoms of Ash Dieback can be reported through TreeAlert in Britain and TreeCheck in Northern Ireland.
Up to 12 million ash trees are found in parks, urban areas, and gardens. It is the owner/manager's responsibility to take action to identify Ash Dieback and deal with the tree, including disposal. However, The Forestry Act 1967 (Section 9(1)) states that the felling of growing trees, including diseased and dying trees, requires a felling licence unless a specific exception to the need for a licence, where certain criteria are met, is applicable, for example, trees growing in a garden, churchyard, orchard or public open space.
Further Reading
https://www.rhs.org.uk/disease/Ash-dieback
https://www.britishecologicalsociety.org/assessing-the-impacts-of-Ash-dieback/