Great yew forests once covered parts of the low-lying Fens

Their disappearance, some 4,200 years ago, may have been caused by a rapid rise in the level of the North Sea which flooded the area with salt water and killed the trees, according to a Cambridge University study.

A team of scientists studied hundreds of tree trunks dug up by farmers ploughing their fields in the low-lying area of Norfolk, Cambridgeshire and Lincolnshire.

The fallen trees, preserved in peat, contain a treasure trove of information about what the Fens looked like in the past.

Scientists say the modern-day Fens were once covered by forest (Image: John Hocknell)

READ MORE: New scheme opens up waterways in the Fens to paddlers

READ MORE: Looking back to disastrous floods in the Fens

READ MORE: Sluice works around the clock to protect the Fens

Most of the wood studied came from yew trees that populated the area between 4,000 and 5,000 years ago.

Analysis by the Cambridge Tree-Ring Unit indicated that some of the trees were 400 years old when they died.

Lead author Tatiana Bebchuk, a PhD student from Cambridge’s Department of Geography, said: “Finding these very old trees in the Fens is completely unexpected – it would be like turning a corner in rural Cambridgeshire and seeing an Egyptian pyramid – you just wouldn’t expect it.

One of the sections of tree trunk studied by scientists (Image: University of Cambridge)

“It’s the same with nature – wood rots and decomposes easily, so you just don’t expect a tree that died five or four thousand years ago to last so long.”

Much of the Fens is barely above sea level, and a sudden rise in sea level around 4,200 years ago would likely have killed the Fen woodlands, according to the researchers.

The period that the Fen woodlands died coincided with major climatic changes elsewhere in the world.

“We want to know if there is any link between these climatic events,” said Ms Bebchuk.

Pieces of ancient wood recovered from the Fens (Image: University of Cambridge)

“We don’t yet know what could have caused these climate events but these trees could be an important part of solving this detective story.”

The Fens were largely a wetland before being drained between the 17th and 19th centuries using artificial drainage and flood protection.

It is now home to some of the most productive farmland in the UK thanks to its rich peat soil.

The research is published in the journal Quaternary Science Reviews.