In some UK woodlands, every young tree has died. What’s going wrong?

Bare oak trees on a winter’s morning in Blenheim Park, Oxfordshire. Researchers have been able to study some areas of ancient woodland around Britain since 1959, which offers a rare chance to monitor long-term change among different species, soil and climate. Photograph: Tim Gainey/Alamy

To the untrained eye, Monks Wood looks healthy and lush in the summer sun. Hundreds of butterflies dance on the edge of footpaths in the ancient Cambridgeshire woodland, which is rich with ash, maple and oak trees. Birds flit through the hedgerows as they feed. A fox ambles through a forest clearing, before disappearing into long grass.

But for a number of years, it has been clear to Bruno Ladvocat and Rachel Mailes that something is missing. In 2022, Ladvocat, Mailes and their research team from Birmingham University were out sampling when they noticed that the small trees that typically cover the woodland floor were increasingly hard to find.