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Updated 9th December 2020

What is Chalara ash dieback?

Chalara ash dieback is a serious disease of ash trees caused by a fungus called Hymenoscyphus fraxineus. The disease affects ash trees by blocking the water transport systems, causing leaf loss, lesions in the wood and on the bark. This leads to the dieback of the crown of the tree. Trees become brittle over time with branches breaking away from the main body of the tree. If they are not dealt with, trees are at risk of collapsing, presenting an immediate danger to the surrounding area.

How long have you had Chalara ash dieback at Westonbirt?

Chalara ash dieback was first identified at Westonbirt Arboretum in 2015, and since then we have been working closely with Forest Research to monitor the infected trees. Chalara ash dieback has now infected ash trees throughout Silk Wood, and to ensure the future health of this ancient woodland we will be removing infected ash trees to make way for new plantings of various species.

What is involved with the removal of ash trees?

In 2019 some initial work was done to remove infected ash trees from main pathways in the arboretum, to ensure the safety of visitors and staff. In early 2021, contractors will be starting on work to remove infected trees from Silk Wood. This will mean that there will be significant changes to Silk Wood over the coming years as we work to ensure the continuing health of the whole woodland. In some areas, we may be removing large numbers of trees, and replanting different species. In other areas, we may try a non-intervention approach.

We have identified and marked any ash specimens that are hopefully showing signs of tolerance to the disease or little die-back. These trees will not be felled and will be monitored going forward.

It is likely large areas of Silk Wood will be closed to members and the public during felling works. This is to ensure the safety of everyone onsite. Timeline and closure details to be made public once we know more.

How large an area are you clear-felling?

About 6 hectares, 800 cubic metres, of ash trees will be clear felled in this next stage over winter 2021. We will leave other species where possible within these clear fell areas.

What machinery are you using to complete the work?

The clear-felling work will be done through use of a harvester. Harvesters are large forest vehicles which have an articulated boom holding a harvester head. This is used to fell and strip the tree's branches, then cut them into logs, in one swift process. It can take a harvester a few seconds to remove a tree meaning this work can be carried out as swiftly and safely as possible to cause the least disruption to peoples visits.

How long will the work take place?

At this point in time we are unable to confirm how long the clear-felling of ash trees in sections of Silk Wood will take. It is hopeful contractors will be able to start early 2021. Once the works commence, we will be able to have a better timescale to relate to our visitors. The work will be completed before bird nesting season (early March).

Am I going to take ash dieback home to my garden after I visit?

We all have a part to play in the prevention of the spread of pests and diseases. Though Chalara ash dieback spreads on the wind-borne spores of the fungus Hymenoscyphus fraxineus, and so there is little we can do to prevent the spread of the disease, the spread of other threats can be slowed or stopped by:

  • Pests and diseases can spread in the mud and debris on shoes, paws and tyres, so simple measures such as cleaning your boots and car wheels after a walk in the Forest can help to limit the spread of diseases.
  • Don’t risk it! Don’t bring any plant or tree products back from trips abroad, because these might be carrying harmful non-native tree pests or pathogens.
  • Be vigilant! Report any trees that you suspect are in ill-health to the Forestry Commission using Tree Alert
  • Join us! You can help us to protect Silk Wood against the threat of pests and diseases by joining the Friends of Westonbirt Arboretum. Your membership fee goes directly back into maintaining Silk Wood and Westonbirt Arboretum for future generations.

Has my ash tree got ash dieback – what should I do?

You can help the Forestry Commission Report monitor the spread of the disease by reporting any trees that you suspect are in ill-health to the Forestry Commission using Tree Alert.

Staff at Westonbirt Arboretum are unable to advise on identification or to confirm whether a tree is infected of trees not within the arboretum. 

Please note that felling ash trees, especially ones that are diseased, is a difficult and dangerous job if done incorrectly. We would urge anyone considering removal of trees from their garden to seek professional help, however we are unable to recommend any particular companies.

Will I get a discount if part of Silk Wood is closed during my visit?

We will not be offering discounts to entry or membership fees while the felling is happening.

Why aren’t you replanting straight away?

In order to allow the soil to recover from the impact of felling and be ready for replanting, the ground will need to lie fallow for several years before replanting can begin. 

All our planting is done over the winter months – generally January and February. Early planting means that the young trees have a chance to settle in with minimal fear of drought, and are well established come the spring.

We will be using this opportunity to assess what species will thrive in Silk Wood and which will create a resilient woodland for the future. There will, therefore, be a certain amount of research and experimentation into what trees we want in Silk Wood in the future.

Until this point, you have had a policy of leaving infected ash trees and monitoring them. Why has this changed?

Chalara ash dieback is a relatively new disease, and we are leading the way in working out how best to manage the disease. Until now we have monitored the trees, looking for signs of tolerance.

As ash trees succumb to the disease their wood becomes increasingly brittle – increasing the risk of falling branches, and making the tree more dangerous for our staff to take down. We now suspect that some of our trees are reaching the point where they need to be removed for the safety of our visitors and of staff. A survey conducted in July demonstrated that around 120 woodland ash, and a number of specimen trees would need to be removed initially, and the larger scale felling would need to start later next year. Taking out the infected ash trees will also give us the opportunity to make way for the replanting of new species that will create a more resilient woodland.

Why don't you just leave the ash trees? Deadwood is good for biodiversity.

As ash trees succumb to the disease their wood becomes increasingly brittle – increasing the risk of falling branches, and making the tree more dangerous for our staff to take down. We now suspect that some of our trees are reaching the point where they need to be removed for the safety of our visitors and of staff. A survey conducted in July demonstrated that around 120 woodland ash, and a number of specimen trees would need to be removed initially, and the larger scale felling will start next year. Taking out the infected ash trees will also give us the opportunity to make way for the replanting of new species that will create a more resilient woodland.

How will you choose which trees to replant with?

We have not yet decided exactly which species of tree we will be replanting with – though our current plans are to replant with natives and near natives. We will work closely with colleagues in Forest Research to determine which species will make Silk Wood resilient to a changing world in years to come and we will continually monitor the species we plant. The information we learn from this project will allow us to share findings and best practise with other organisations and woodland managers in the UK and abroad.