Ancient pollen helps scientists to reimagine Europe’s landscape before humans

What did Europe look like before modern humans arrived? Many might imagine a lush, unspoiled forest that stretched from the Atlantic Ocean to the Ural Mountains, but evidence from ancient pollen suggests that ancient Europe’s temperate forests were interspersed with large swaths of open plains, meadows and heathlands.

Using samples from the bottoms of lakes across Europe, a team of scientists reconstructed the continent’s landscape during the last interglacial period about 120,000 years ago – the last time Europe was free from ice ages before the dominance of Homo sapiens.

This new research, published in November in Science Advances, points to the work of non-human ecosystem engineers. Scientists suggest that these open spaces resulted from now-extinct grazing animals.

This is an important insight if conservationists hope to recreate the “dynamic, shifting, mosaic landscape” of the last interglacial period, says ecologist Elena Pearce, lead author and a Postdoctoral Fellow at Aarhus University who studies the landscapes of the past. “Europe never looked one particular way.”

Pond goo and rewilding Europe

Conservation and rewilding projects require understanding how humans have changed the environment, Pearce explains. Researchers turn to an unlikely resource to establish pre-human baselines for nature – pond goo.

Airborne pollen from trees, grasses and other plants “settles on the surface of lakes or bogs,” Pearce says – that eye-watering yellow film that covers bodies of water in the springtime. Some of that pollen ends up drifting all the way down to the bottom, “and then it builds up in sediment over years and years and years,” creating layers that specialists called palynologists can read like a book.

Palynologists take cores of lakebeds, cylindrical samples like the ice cores that allow Arctic scientists to track changes to the climate over deep time, to collect the stratified layers of ancient pollen. Analysing ancient pollen samples is meticulous work – each tiny grain must be identified by eye under a microscope, and the diversity of families and species the palynologists have to distinguish between is staggering.

Pearce gathered pollen data from 96 lakes and bogs across Europe, spanning 16 modern-day countries. Although many previous studies have relied on the ratio of arboreal pollen to non-arboreal pollen to predict what the environment might have looked like, Pearce used a statistical model to account for differences between plant species – how much pollen they produce and how that is dispersed throughout the landscape.

And by examining the plant species present in the pollen samples – many of which could be in your backyard today – Pearce inferred about the landscape based on those plants’ needs. For example, oak trees indicate more open vegetation since they cannot abide by shade, and the presence of shade-tolerant trees such as hornbeam would suggest a closed-canopy forest.

A patchwork Europe

The picture of ancient Europe that emerged from Pearce’s model does not look like today’s national parks.

Light woodland and open vegetation such as plains or meadows covered more than half the landscape, Pearce found. And even more surprisingly, ancient precipitation patterns and climate did not seem to substantially determine where these grasslands formed.

Pearce says she initially suspected fires might be the driver – but that would have left telltale streaks of charcoal in the lakebed cores since smoke settles on the surface of water the same way pollen does.

Instead, the evidence points to other ecosystem engineers: large grazing animals that nibbled on young trees and kept forests in check. “Large animals not only reduce vegetation but also disperse seeds and add nutrients to the soil,” Pearce explains. “It is really revealing that certain processes are missing from today’s landscapes – today, if you leave an open patch of land, you will probably end up with a forest environment.”

Where the elephants roam

Which ancient grazers created the plains of interglacial Europe? Some of these ecosystem engineers are familiar faces, Pearce says – such as fallow deer, which still roam wild in Italy, Turkey and much of the Balkans; and European bison, which have a stronghold in Poland and Belarus.

Others went extinct relatively recently, like the aurochs, an ancestor of modern cattle that died out in the 1600s.

But the ecosystem engineers that most capture Pearce’s imagination are the straight-tusked elephants – a species of pachyderm scientists estimate could have weighed up to 17 tonnes that plodded around Europe in the last interglacial period.

These ancient elephants, whose bones likely inspired myths of giants and cyclops, would have to consume mountains of vegetation to sustain their bulk. In addition to their voracious grazing, elephants could change their surroundings in ways a fallow deer cannot. “Elephants can knock down trees,” Pearce says. “Few animals that are still alive today in European landscapes can have that kind of impact.”

Environmental disruption, whether from wildfires or large animals, is great for biodiversity. “What these animals are doing is churning things up, grazing some areas, leaving other areas,” and generally creating a range of habitats that can support a wide variety of species, Pearce explains.

Not an ecosystem prescription

The discovery that grasslands were an important part of the ancient landscape should not be taken as a prescription to stop planting trees, Pearce says. “If the last interglacial period did have between 25% and 50% closed forests, then we are still missing a load of that,” she adds.

But forests aren’t the only form of nature Europe should aim for, Pearce explains, and there are already programmes to reintroduce large grazing animals, such as horses released in Denmark’s Mols Bjerge National Park.

But the results of these programmes have been mixed – these populations are “really threatened by people not wanting to live with these large animals,” she says.

If these animals are considered “too wild for Europe, then we are placing all of the pressure to live with these wild animals to maintain our diversity in species on the Global South,” she says.

The likelihood of the ancient European plains returning is slim if modern Europeans have a hard time getting along with wolves and horses as neighbours, Pearce adds – “let alone anything like an elephant.”