To the untrained eye, Monks Wood appears vibrant and flourishing beneath the summer sun. Along the edges of the footpaths in this ancient Cambridgeshire woodland, hundreds of butterflies flutter through the air. Ash, maple and oak trees thrive in abundance, birds dart through the hedgerows in search of food, and a fox strolls leisurely through a clearing before vanishing into the tall grass.

Yet for some time now, Bruno Ladvocat and Rachel Mailes have noticed that something vital is missing. In 2022, while carrying out sampling work with their research team from the University of Birmingham, they realised that the small trees typically carpeting the woodland floor were becoming increasingly scarce.

Today, in the dappled light beneath the tallest trees, areas once filled with dense clusters of saplings stretching upwards for sunlight now lie bare.

This phenomenon is not unique to the 157-hectare (388-acre) site. From Buckholt Wood in Monmouthshire to Glen Tanar in the Cairngorms, new research from eight ancient woodlands across the UK reveals a deeply troubling pattern: these forests are struggling to regenerate.

Despite the considerable variation in tree species, soil conditions, rainfall and temperature across the study sites, all were exhibiting the same trend — sapling mortality was on the rise.

Mailes, a postgraduate researcher and co-author of the research, says: “We could see as we were going through the forest that there wasn’t a lot of regeneration coming back up. I had the sad job of crossing off all the saplings that we couldn’t find or that we were finding dead.

“Across a lot of different species, they were just not coming back. It really made us think: there’s a problem here. Then we ran all the data and we could see that we were right,” she says.

According to the study, which is currently undergoing peer review, the annual mortality rate of saplings has increased by 90%, rising from an average of 16.2% before 2000 to 30.8% by 2022.

This decline in survival means the average sapling now has just a 15.8% chance of surviving five years — down from 41.3%. Over the same period, the number of small trees successfully establishing themselves dropped by 46%. At two sites — Denny Wood in the New Forest and Dendles Wood on Dartmoor — not a single sapling within the monitored areas has survived since 1995.

The findings are based on rare long-term data, with the same areas of ancient woodland monitored continuously since 1959. This unique dataset has enabled scientists to track ecological changes over more than six decades, prompting growing concern over the long-term health and resilience of Britain’s woodlands.

Several factors may be contributing to the decline, including climate change, disease, and overgrazing by deer. Periods of drought and extreme heat have become increasingly common, placing additional stress on young trees. Moreover, the rate of biomass loss is accelerating across many sites. Mortality among the largest trees has also increased, from 0.5% per year to 0.8% — meaning that, on average, one in every 125 of the largest trees now dies annually, compared with one in 200 previously.

This has serious implications for carbon sequestration, as the capacity of woodlands to absorb carbon from the atmosphere is beginning to diminish.

“I look at this as a big worry,” says Ladvocat. “Even in areas which are relatively open, where you would expect to see new trees coming up and more trees surviving, we see less coming up and more dying.

“These forests are in a moment that makes them more vulnerable to the challenges they are facing, such as climate change and new pathogens. If there’s an external force that starts killing a lot of big trees around them, then there might not be enough saplings and small trees to replace them,” he says.

Deeper into Monks Wood, a clearing reveals another pressure facing ancient forests: a stand of ash trees, grey and skeletal, all victims of ash dieback — a fungal disease. The canopy here is entirely bare, exposing an uninterrupted view of blue sky overhead.

Ash dieback is expected to kill up to 80% of the UK’s ash trees in the coming years. In Monks Wood, the situation is so severe that researchers must wear helmets when stepping off the path, to protect themselves from falling branches. On closer inspection, many other ash trees in the woodland are clearly infected.

While concerns about forests’ ability to regenerate in a warming world are not new, the researchers note that data remains limited and the topic has been significantly understudied.

“The conditions of these forests are not unlike those of other forest remnants across Great Britain and much of Europe. That’s why it’s concerning,” says Ladvocat. “These changes may be more widespread than what we were able to detect with our current dataset.”

Ladvocat and Mailes are part of Membra, a project based at the University of Birmingham that seeks to understand how trees retain and pass on memories of environmental stress — and how this knowledge might inform more effective woodland management.

Their aim is to find ways to help Britain’s woodlands withstand the growing pressures of a changing climate. One avenue of research involves identifying genetic markers in seeds that improve survival rates, potentially allowing the creation of a form of “bootcamp” for seedlings — a training process that could help future forests become more resilient.

“There is still hope for these forests,” Ladvocat insists. “They are still absorbing carbon; they still have lots of species that are connected to people’s history. There is a possibility that this can be reversed, possibly with the help of people.”

 

——————————————————————————

At Natural World Fund, we are passionate about restoring habitats in the UK to halt the decline in our wildlife.