Finding solutions to the UK's oak generation gap

Action to support recovery and growth...

This edition of Tree Talk welcomes a guest post from Professor Melanie Smith, Research Coordinator at our friends, Action Oak.

Our two native oak trees in the UK, Quercus robur (pedunculate oak) and Quercus petraea (sessile oak) are an important part of the UK’s biodiversity, heritage, and economy, providing key services for the environment and society.

Our native oak trees provide habitat for more than 2,300 other species including birds, fungi, insects, lichens, and mammals. 326 of these species are obligate, depending on pedunculate and sessile oaks for their survival. A further 229 are highly associated. Oaks are also a key species of our endangered temperate rainforest habitat that is found along the UK’s Atlantic coast. Temperate rainforest is globally rarer than tropical rainforest.

We have more ancient native oaks than all other European countries combined. Over 65,000 ancient, veteran, and notable oak trees have been recorded. Every one of these trees is home for a unique, important and diverse ecosystem that has developed over thousands of years, associated with a continuum of oak trees growing in the same locations. Even when the trees die, the deadwood remains, providing a complex habitat above and below ground.

But we have an Oak Generation Gap. Middle aged oaks, 200-300yrs old, are scarce in both woodland and open landscapes. This generation gap disrupts the continuity of oak ecosystems and threatens the long-term survival of species that use oaks. This would be a significant loss to people and the environment.

Oak’s contribution to the UK economy has been valued at about £700,000,000 (£0.7 billion) of environmental, social and economic benefits per year. However, this is likely to be an underestimate, as the full cultural, natural and heritage value needs further evaluation.

The UK’s native oak trees provide habitat for more than 2,300 other species, like this red admiral butterfly

In the UK we have around 172m oak trees and, with a human population of just under 69m, that is around 2.5 oaks per person; not many oaks to ensure we will continue to benefit from oaks in the future. Our oak trees are under pressure which means the number of trees could further decline unless we take action to support recovery and growth across oaks of all ages, especially finding solutions for the oak generation gap. They are facing many threats, biotic and abiotic, including shifting pest and disease ranges, extreme weather, climate change, mammal damage and decline syndromes among others. These threats can compromise oak health and cause fatalities.

Climate change is one of the most significant pressures to oak forests and individual trees. Rising temperatures, altered rainfall patterns, and more frequent droughts can weaken trees, reduce growth rates, and increase mortality. Climate stress also makes oaks more susceptible to secondary threats like pests and diseases. Research has shown that drought stress is becoming an increasingly important factor in Acute Oak Decline.

Acute Oak Decline (AOD), an emerging decline syndrome first observed in the late 20th century, appears to be driven by a combination of environmental stressors along with biotic interactions. As of 2023, there were 394 sites recorded with AOD in the UK (Figure 1). It can be fatal for the oak tree within an alarming timeframe of as little as 3-6 years. For a tree that could live to 1000 years old, to die within 6 years is a rapid deterioration. Improved understanding of the conditions for AOD spread will help implementation of mitigation measures.

Figure 1: Confirmed sites with Acute Oak Decline. Credit Forest Research 2024, Crown Copyright.

Increased environmental pressures like climate change, exacerbate the threats from pests and diseases like AOD, other decline syndromes, Oak Processionary Moth (OPM) (see Figure 2 for current distribution), fungal infections, bacterial diseases, and wood-boring insects. These organisms may not kill healthy trees immediately, but they can cause severe damage when trees are already stressed.

Several high-risk possible invasive species are not yet present in the UK and may pose an ecological and economic threat if they become established. For example, a priority insect pest is the oak lace bug (Corythucha arcuata). It is a sap-sucking species native to North America that has been introduced to mainland Europe. Effective surveillance for these threat species is key to early detection and taking action to mitigate and remove them before they become established. Citizen scientists are very involved in these threat detection efforts through projects like Observatree and TreeAlert.

Figure 2: Current distribution of OPM infested oaks (2024). Forestry Commission, Arcgis map Crown Copyright.

This is just a tiny snapshot of what is happening with our native oaks. They are as complex as their lives are long, and we need to take proactive steps to ensure their survival for future generations.

Action Oak exists to safeguard the future of our oaks. Our mission is to lead the vital research needed to better understand the threats facing the UK’s native oak trees, helping to protect our oaks for generations to come.

You can read more about our oaks, and the threats they face in our State of the UK’s Oaks report, published earlier this year.

We invite you to join us in protecting our oaks.

Professor Melanie Smith is the Research Coordinator for Action Oak. Follow Action Oak on socials: Instagram, Facebook, LinkedIn and Bluesky. Sign up to the newsletter or make a donation.

MORE: Tree Health Forum - Spring & Summer 2026

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