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Acute oak decline

Our native oaks are under pressure like never before. They are declining at an unprecedented rate due to drought, flooding, pollution, pests and diseases.

Acute oak declines have occurred for centuries, but acute oak decline is a novel type of oak decline which was first defined in the UK in 2014.

Credit: Graham Prentice / Alamy Stock Photo

Acute oak decline involves combination of factors which cause oak trees to become stressed and bacterial species which may be causing bleeding cankers.

Credit: Rebecca Gosling / WTML

Acute oak decline involves loss of leaves and thinning of the crown of the tree.

Credit: Rebecca Gosling / WTML

Quick facts

Common name: acute oak decline

Scientific name: none

What does it affect?: English oak and sessile oak

Areas affected so far: southern England and Wales

Origin: none

What does acute oak decline look like?

Oak declines are a complex phenomenon that have occurred a number of times across Europe over the last 200+ years. The current decline in the UK has been observed over the last 20 or so years. Trees over 50 seem to be the worst affected and mature trees can die within five years.

Symptoms include:

  • General thinning of the crown as leaves are lost. This can be quite sudden, occurring over a two-year period.
  • Cracks in the bark.
  • Dark fluid and extensive weeping patches that seeps through vertical cracks between pieces of bark and runs down the trunk or stem.
  • Stem bleeds that can stop and heal as the tree recovers from a stressed state.
  • As the tree becomes stressed, secondary pests and diseases begin to take advantage of the weakened tree.

What is acute oak decline?

Acute oak decline is a novel type of oak decline which was first defined in the UK in 2014. It involves combination of factors which cause oak trees to become stressed and bacterial species which may be causing bleeding cankers.

The causes behind acute oak decline are still being researched but environmental stresses like soil conditions, drought, waterlogging and pollution can all impact the tree. Insects, fungi and bacteria then move in on the vulnerable tree and push it into decline.

Credit: Martin Fowler / Alamy Stock Photo

What happens to the tree?

Symptoms of acute oak decline are essentially the tree's response to stress. They are a thinning crown as leaves are lost, cracks in the bark, and dark bleeds that may run down the trunk. If the stress is severe or prolonged, the tree can reach a tipping point where it runs out of energy to get through the winter or fight off pests. These trees can die within a few years.

Where has acute oak decline impacted?

Oak declines have been observed since the 1700s but this unique type of oak decline was forest reported in the UK in 2014.

In the UK, acute oak decline has been observed across the southern parts of England and Wales. As environmental conditions become more unpredictable, cases of acute oak decline might increase. Declines in other tree species might also occur.

How did acute oak decline get here and what impact will it have?

Oak declines don’t ‘arrive’ as such, but changes in environmental conditions have caused them to come about. The evidence suggests that oak declines might become more frequent and severe as the climate changes. More frequent environmental changes like prolonged periods of drought or waterlogging will make the problem much worse.

What are we doing about it?

To combat acute oak decline, we are planting oaks as much as possible. In addition, we plant in areas where oak can naturally regenerate to make sure the next generation of trees is better adapted to our changing climate.

As well as this work, we have:

  • Developed a UK and Ireland sourced and grown assurance scheme to make sure all the trees we plant and sell are produced in the UK and Ireland. This reduces the risk of importing new pests and diseases that could add stress to our native oaks.
  • Funded research on the causes of oak decline in the UK.
  • Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.
  • We’re part of the Action Oak partnership, an initiative to protect the UK's oak trees.

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