Scientists have discovered the oldest known fossil forest on Earth. Dating back approximately 390 million years, the ancient trees reveal how the arrival of the first forests began transforming not only life on land, but the landscape itself.

Today, forests cover vast areas of the planet.

But there was a time when there were no forests at all.

During the Devonian Period, between roughly 419 and 358 million years ago, plants underwent an extraordinary transformation. Small vegetation was gradually joined by larger tree-like organisms, and the first forests began to appear.

Researchers from the University of Cambridge and Cardiff University have now discovered evidence of the oldest fossilised forest yet known.

It was found not in some unexplored wilderness, but in sandstone cliffs along the Devon and Somerset coast of South West England.

390 million years old

The forest dates from approximately 390 million years ago.

That makes it around four million years older than the previous record holder, a fossil forest discovered in New York State.

The British site therefore provides scientists with an exceptionally early glimpse of a world in which trees were only beginning to reshape terrestrial environments.

The fossils were discovered in the Hangman Sandstone Formation, near Minehead on the southern side of the Bristol Channel.

Researchers found fossilised logs and plants, traces of roots, tree stumps and large quantities of plant debris preserved in the rock.

A forest unlike anything alive today

Walking through this forest 390 million years ago would have been a strange experience.

Its trees were called Calamophyton.

At first glance they might have looked somewhat like palm trees, but they were not palms — and they differed dramatically from modern trees.

They had relatively thin trunks that were hollow in the centre. They did not possess conventional leaves. Instead, their branches carried hundreds of small twig-like structures.

They were also modest in height.

The largest reached only around two to four metres.

There was no grass beneath them and essentially no undergrowth comparable to that of a modern forest.

Professor Neil Davies, from Cambridge’s Department of Earth Sciences and first author of the study, described it as a very unusual forest unlike anything we would encounter today.

Trees began changing the Earth

The discovery is important for a reason that goes beyond setting a record.

The researchers could study the trees in the environment in which they actually grew.

That allowed them to investigate how some of Earth’s earliest forests interacted with their surroundings.

Trees do not merely occupy landscapes.

They create and modify them.

Their roots stabilise soil and sediment. Their trunks interfere with moving water. Their branches fall to the ground and accumulate. Forest vegetation changes erosion and the way rivers transport sediment.

The Somerset fossils capture an early stage of this enormous transformation.

Before forests, rivers behaved differently

The landscape surrounding the ancient forest was a semi-arid plain crossed by small river channels flowing from mountains to the northwest.

The dense stands of Calamophyton shed enormous quantities of twigs and other plant material.

This debris accumulated in the sediment.

The researchers found evidence that vegetation was already influencing how sediment accumulated and how water moved across the landscape.

According to Davies, the fossils preserve a crucial stage in Earth’s history when rivers began operating in a fundamentally different way.

This means that the evolution of trees did not simply create a new habitat for living organisms.

It changed physical geography.

The Devonian revolution

The Devonian Period represents one of the great transitions in the history of terrestrial life.

Plants had colonised land much earlier, but during the Devonian they became larger and structurally more complex.

By the end of the period, seed-bearing plants had appeared, while land animals — particularly arthropods — had become well established.

Forests also began affecting the atmosphere, soils, rivers and the global cycling of nutrients.

The new fossil site captures the beginning of that process.

The underlying scientific study concludes that these early tree communities acted as “biogeomorphic agents”: living organisms capable of physically altering the landscape around them.

A forest floor covered in twigs

Modern forests produce enormous quantities of leaves.

This ancient forest produced something different.

Calamophyton trees continually shed branches and twig-like structures.

As densely packed trees dropped this material, the forest floor accumulated large quantities of biological debris.

That created new environments for other organisms.

The researchers found evidence of invertebrate activity associated with the forest floor, illustrating how the appearance of trees could create entirely new ecological opportunities.

Britain was somewhere else

There is another important difference between this ancient landscape and modern Somerset.

It was not located where Britain is today.

During the Devonian, the region that would eventually become southwest England lay much farther south and was connected geographically with areas that today form parts of Germany and Belgium.

Similar Devonian fossils have been discovered there.

Continental drift subsequently carried these rocks across the planet until they became part of the British landscape.

The cliffs therefore preserve an ecosystem that existed hundreds of millions of years before Britain itself existed in anything resembling its modern form.

An unexpected discovery in familiar rocks

Perhaps one of the most remarkable aspects of the discovery is its location.

British geology has been studied intensively for centuries.

Scientists had previously assumed that this particular sandstone formation contained relatively little significant fossil plant material.

The new research showed the opposite.

The formation contains extensive evidence of Devonian plants and their interaction with the landscape.

As Davies observed, even rocks that scientists think they know well can still produce major discoveries.

When trees started engineering the planet

The importance of the world’s oldest known fossil forest is therefore not simply its age.

It records a moment when life became an increasingly powerful geological force.

Before forests, rivers encountered mostly bare landscapes.

After trees spread across the continents, roots held sediments together, vegetation obstructed water, organic material accumulated and ecosystems became more complex.

The planet began to look and behave differently.

The strange Calamophyton trees preserved in the cliffs of southwest England were modest compared with the forests that would eventually follow.

But they were among the pioneers of a transformation that continues to shape the Earth today.

Source: Based on “Earth’s earliest forest revealed in Somerset fossils,” published by the University of Cambridge on 7 March 2024. The research was carried out by scientists from Cambridge and Cardiff University. The underlying study by Neil S. Davies, William J. McMahon and Christopher M. Berry, “Earth’s earliest forest: fossilized trees and vegetation-induced sedimentary structures from the Middle Devonian (Eifelian) Hangman Sandstone Formation, Somerset and Devon, SW England,” was published in the Journal of the Geological Society.