Chalara Ash Dieback at Westonbirt Arboretum


In 2015 Westonbirt staff identified Chalara ash dieback within the woodlands of Silk Wood. A disease which has been sweeping across Europe since 1992 which kills ash species. The top area of Silk Wood, beyond Broad Drive, is part of our response: a fight back to ensure a healthy, diverse and resilient woodland in the future.

2021 saw the start of major silvicultural work to remove infected ash trees. This is a highly managed approach which includes three management techniques:

  1. Clear fell and replant areas with large amounts of infected ash trees
  2. Thinning, where possible only remove infected ash and leave space for natural regeneration of other species
  3. Non-intervention to allow us to research the effects of the disease

Despite the dramatic looking change, the approach to clear fell large areas of infected ash trees is a positive step for the woodland. In woodland terms, the removal of ash trees on such a large scale is quite a shock to the ecosystem; but doing this now gives us the best possible chance of creating a resilient woodland in future through a considered replanting programme.


Watch our videos below to learn more about how we are managing Chalara ash dieback at Westonbirt Arboretum.

Heliexpert The Drone Company

Replanting Silk Wood

Clear fell areas will be left fallow for a couple of years to allow the ground to recover, and give us time to choose the best species to replant with. We are working with colleagues in Forest Research on which tree species will be best suited to this environment and offer the most ecological benefits; including native and near native woodland species that will be resilient towards pests and diseases and our future climate.

In some cases we may look to plant species that have a more southerly provenance (eg a beech tree from Italy!). For some species, the changing climate here means it will thrive coming from hotter climes; for others which are long lived, we would see that the future generations of that specimen will adapt to our environment; both approaches leading to a far more resilient future woodland.

Chalara ash dieback at Westonbirt Arboretum video

Chalara ash dieback was prevalent throughout Silk Wood at Westonbirt Arboretum. In order to ensure the future health of this ancient woodland, Forestry England was faced with having to respond to this threat to maintain the health of Silk Wood for future generations. This involved removing infected ash trees to make way for new plantings of various species, which will help to create a resilient woodland.

Video credit: Heliexperts The Drone Company

Heliexpert The Drone Company

Want to find out more about Chalara ash dieback? Visit the pest and disease resource from Forestry Research.

Find out more

The Silk Wood Project video

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 February 2021 work began to remove infected ash trees from Silk Wood. There will be significant changes to Silk Wood over the coming years as we work to ensure the continuing health and resilience of the whole woodland.

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

Tree Alert

Monitoring tolerance to Chalara ash dieback video

This does not mean that the ash tree has disappeared from Silk Wood all together – in some areas Fraxinus excelsior (known as European ash or common ash – which is the disease most affected by Chalara ash dieback) will be retained to monitor the progression of the disease. We have 23 other exotic species of ash which will remain and be carefully monitored for tolerance to the disease. We’ll also continue to monitor native ash specimens that show signs of tolerance.

Discover how Forestry England are safeguarding trees from pests and diseases and protecting their future.

Find out more

Map of Silk Wood with coloured areas depicting the Silk wood Management plan

Silk Wood Management map

Red: Clear fell and replant (6.74ha)
Large scale removal of infected ash trees. Through clear felling we have given Silk Wood the best possible chance to replant these areas for a more resilient woodland to face future climate challenges. These areas will remain fallow for a couple of years to allow the ground to recover. 

Amber: Thinning (22.78 ha)
Where possible we are looking to only remove dead or dying ash trees, aiding natural regeneration allowing healthy species to grow.

Green: Non-intervention (3.51 ha)
Areas away from visitors will be left, allowing us to monitor and research how the disease develops within ash trees.

Blue: Coppice
We have 22 hectares of actively managed coppice coups.

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:  

  • Keep it clean! 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 donation goes directly back into maintaining Silk Wood and Westonbirt Arboretum for future generations.