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Ash Dieback


The Earth Trust is very concerned about the confirmed occurrences of the Chalara dieback fungus on ash trees in Britain. Ash trees are native to Britain and are important within sustainably managed woodlands and forests, providing both economic and biodiversity benefits.

Hymenoscyphus fraxineus

The past decade has been a tough one for trees in Britain. A number of pests and diseases are becoming increasingly prevalent, with much news in the media regarding acute oak decline, the oak processionary moth, chestnut bleeding canker, red band needle blight, and numerous Phytophthora species. The arrival of ash dieback in the UK gave further cause for concern. This is a fungal disease of ash trees (Fraxinus species) caused by Hymenoscyphus fraxineus (formerly known as Chalara fraxinea). It was unknown in Great Britain until 2012, when the first case was confirmed in a nursery in Buckinghamshire on ash seedlings imported from The Netherlands. Since then it has spread further around the country.   

The disease causes leaf loss and crown dieback in affected trees, and can lead to tree death. It is also particularly destructive of young ash plants, killing them within one growing season of symptoms becoming visible. Older trees can survive initial attacks, but tend to succumb eventually after several seasons of infection. The Forestry Commission is treating H. fraxineus as a ‘quarantine’ plant pathogen, which means they can enact measures to contain or eradicate it when it is found. 

Local spread may be via rain splash or transmission by insects. Over longer distances the risk of spread is most likely to be through the movement of diseased ash plants. Movement of logs or unsawn wood from infected trees might also be a pathway for the disease. It is potentially a very serious threat and has caused widespread damage to ash populations in continental Europe, including estimated losses of 60-90% of Denmark’s ash trees.

The Forestry Commission have produced an exotic pest alert sheet and photo guide which provide more information on how to identify the disease and what you should do.  

Suspected cases of Chalara dieback of ash should be reported to Forest Research Tree Health Diagnostic and Advisory Service: 01420 23000 or ddas.ah@forestry.gsi.gov.uk.

What we are doing: The Living Ash Project

Over the last 20 years the Earth Trust has been developing populations of tree species, including ash, that will be resilient to existing and novel diseases and pests. We advocate the planting of such trees with a diverse genetic base, to provide our woodlands with the necessary robustness to withstand future diseases. In collaboration with the Future Trees Trust and Forestry Commission, the Earth Trust has planted around 60,000 trees in Paradise Wood, which is now the largest collection of hardwood forestry genetics trials in Britain. Earth Trust is also leading the Living Ash Project which is screening ash trees and implementing a breeding programme of tolerant trees.

A way forward...

The struggle to control the impact of pests and diseases in trees is, in part, an evolutionary battle, matching genetic variation within tree species against the negative impacts of other organisms. Although trees have largely coped in the past, this struggle has now intensified through human activities. These have degraded tree populations, resulting in adverse effects on their regeneration and increased dispersal of pests and pathogens around the world.    

Compared to the financial costs of direct intervention to combat each new threat, the most sustainable long-term strategy for managing tree health is to exploit the high natural genetic diversity within tree species to develop resilient populations. This is a fundamental part of what Earth Trust has been doing over the last 20 years in our tree research. We place great emphasis on the genetic diversity of our seed orchards, not just for ash, but for all species that we work with. Ensuring a broad genetic base in all our populations and seed – far broader than in any commercial seed lot – will provide resilience to whatever the future throws at our trees, be that a novel disease such as Chalara, or combating climate change though adaptation. Indeed, work in Denmark, where the disease has been prevalent in the last decade, shows that there is a degree of resistance within genetically diverse populations, which gives hope for a future based on diversity.     

Please support the Earth Trust's work to protect British ash trees!

Click Donate now to donate securely online via JustGiving or call 01865 407792 (office hours are 9am-5pm, Monday to Friday).

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