Protection from exotic pests and diseases

Buying trees that have never been overseas is one of the simplest and most effective ways of protecting trees from new pests and diseases.

When new species are imported from overseas, our native trees may have no natural defences against them. What’s more, the predators that keep these exotic species in check in their natural range may well not be present either. This means pest and disease outbreaks can have a devastating impact on our trees and woods.

The threat is so great that almost all of the native tree species in the UK have been affected by an introduced pest or disease in the last 30 years. The UK Plant Health Risk Register indicates that there are a further 127 high risk pests and diseases that would have a high impact to the UK’s woods and trees if they got into the country.

Did you know?

Once a new pest or disease species becomes established, it can rarely be completely eradicated.

How do exotic pests and diseases arrive in the UK?

Most introductions of exotic pests and diseases are down to their inadvertent movement within the trade of plants, timber and wood products. They piggy-back on the wood and plants that are brought in intentionally. For example, ash saplings infected with ash dieback were traded across Europe through the 2000s.

There has been a significant rise in the incidence of serious pest and disease introductions into the UK since 1990 – coinciding with the increase in plant and tree imports from the EU and beyond.

1,117,696
Oak trees imported into the UK between 2013 and 2015

Credit: Blickwinkel / Alamy Stock Photo

Oak processionary moth

Oak processionary moth started causing issues on oak trees in northern Europe in the early 2000s. Despite this, the UK continued to import oak. As a result, oak processionary moth has been inadvertently imported many times since 2007, including the discovery of a nest at the Chelsea Flower Show in 2016. It is now widespread throughout London.

Border controls for plant pests and diseases are insufficient to keep out known pests and diseases, let alone unknown ones. Detection is virtually impossible.

What's the link with climate change?

The expected loss of trees due to imported pests and diseases is jaw-dropping, and a significant problem when it comes to fighting climate change.

To meet our climate change targets, the UK needs at least 1.5 million hectares of additional woodland by 2050 and we’ve got an uphill fight to simply maintain where we are today.

If new pests or diseases reach the UK, the effort to increase tree cover will become increasingly more difficult and expensive, as we work harder than ever to simply stay still.

The UK will lose millions of trees because of exotic pests and diseases

The number of trees the UK stands to lose in the next 10-20 years due to ash dieback alone...

150 million
Mature trees
2 billion
Saplings

How does it affect nature?

If millions of our native trees are lost due to imported pests and diseases, it will have a huge knock-on impact on the native wildlife that relies on trees.

For example, oak and ash are keystone species of our woodland habitats. Ash supports 44 species which cannot be supported by other tree species, and oak supports 326 species which cannot be supported by other tree species. Many more species use these trees in combination with other trees.

Credit: Alex Hyde / naturepl.com

If ash and oak suffer catastrophic declines so, too, do the species that rely on them. And this loss of biodiversity has the potential for far-reaching impacts on nature.

What's the solution?

The simplest thing we can do to reduce the risk of new pests and diseases reaching the UK is to plant trees that have never travelled overseas.

Ideally, trees planted in mainland Britain should be sourced and grown in mainland Britain.

Taking this step drastically reduces the likelihood of pests and diseases arriving in shipments of saplings or seeds brought in from overseas.

The same applies to plants, including horticultural favourites, because pests and diseases have the potential to spread to other species. Xylella fastidiosa is a disease found in olive trees, and lavender and rosemary plants. The disease also impacts some broadleaf trees including oak, so the risk to our native woods is enormous.

What can I do to help?

The biggest impact you can have as an individual is to use your purchasing power.

It can be as simple as asking a question in store:

"Please can you tell me whether the trees on sale here have been sourced and grown in the UK?"

You may get some blank looks - it might be the first time they have been asked the question. By simply asking them you will help to create change. Positive changes will happen when there is both an understanding and a demand.

Also, watch out for trees that have only been sourced (not grown) in the UK. This means the seed came from the UK but was grown abroad before returning for sale. Likewise, trees that are grown in the UK (but not sourced) are where the seed was imported before being grown in the UK. Both of these options still come with risks.

If they don’t have any trees sourced and grown in the UK then don’t despair - you might find what you’re looking for in the Woodland Trust shop. And, you can shop with confidence as all of our trees are certified UK sourced and grown.

Or, if you're buying directly from a nursery, we've developed an assurance scheme to help you identify which nurseries you can trust.

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We have single trees and tree packs to meet your needs, from wildlife to woodfuel. Delivery is free.

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