New evidence in Europe: open grasslands, not pre-human forests

Newswise — Biology and forestry textbooks make it clear that large parts of Europe would naturally be covered in dense forests.

The classic story is that our ancestors cut down the forests, drained the swamps and cultivated the moors. In other words, they created the varied landscapes of meadows, heaths and meadows that characterized our cultural landscapes before the advent of modern agriculture.

But new research from Aarhus University suggests that’s not the case. Elena Pearce, postdoctoral researcher at the Department of Biology at Aarhus University and lead author of the study, explains.

“The idea that the landscape was covered in dense forests across most of the continent is simply false. Our results show that we need to reassess our view of European nature,” she says, and her colleague and co-author, Professor Jens-Christian Svenning, continues:

“Nature during the last interglacial period – a period with a mild climate similar to today, but before the arrival of modern humans – was full of variation. Importantly, the landscapes supported large amounts of open and semi-open vegetation with light-demanding shrubs, trees, and grasses, as well as stands of tall shade trees.

Glacial and interglacial periods

Variations in Earth’s orbit around the sun and shifts in tectonic plates mean that our planet is impacted by extended periods of colder temperatures. We call these periods ice ages or ice ages.

Researchers agree that there have been at least five major ice ages over the four billion years of Earth’s history. The first ice age was about 2 billion years ago and lasted about 300 million years.

Although it may seem confusing, we are currently experiencing a very significant ice age. Researchers also divide ice ages into cold and warm periods, namely individual ice ages and intermittent warmer periods, interglacial periods.

The current ice age has lasted for almost 2.6 million years, but we are currently in an interglacial period, now exacerbated and likely prolonged by human emissions of greenhouse gases. The study focuses on the previous interglacial period, which lasted from 129,000 years ago to about 115,000 years ago. In Europe, this interglacial period is called Eem.

Sources: National geographic

Ancient pollen samples reveal what nature was like

Samples of ancient pollen helped the research team identify which plants were growing more than 100,000 years ago during the last interglacial period.

The research group integrated data from pollen samples from large parts of Europe. The samples reveal that plants that do not thrive in dense forests are often important parts of the vegetation.

“Large shade trees such as spruce, linden, beech and hornbeam will be more common in dense forests. However, the results show that hazel trees often covered large areas of the landscapes. The hazel is a bush that does not grow in large quantities in dense forests,” explains Jens-Christian Svenning.

In the plant world, competition for access to sunlight is fierce. The trees with the tallest crowns can capture the most sunlight and win this competition. In beech forests, the trees absorb almost all sunlight. This means that other smaller trees and shrubs, such as hazel, cannot grow in a beech forest.

“The hazel thrives in open country and open or disturbed forests, and is tolerant of disturbance by large animals. While species like beech and spruce are often seriously damaged or killed by cutting or grazing, hazel can survive without problems. Even if you cut down a hazel tree, it will still produce a lot of new growth,” he says.

“For this reason, hazel was often very common in historic copses.”

What pollen can reveal about the past

Almost all trees, flowers and shrubs give off pollen. Pollen is to plants what sperm are to animals. For a plant to produce seeds, its eggs must be pollinated.

Pollen is spread by wind or insects.

Much of the pollen lands on the ground, where it cannot pollinate other plants. Instead, it is eaten by insects or broken down by microorganisms. However, a small amount of pollen ends up in lakes, bogs or streams, where it falls to the seafloor.

Beneath the surface, there is often no oxygen or life, and pollen is preserved for hundreds of thousands of years in the soil layers.

By examining the composition of different types of pollen in the soil layers of ancient, buried wetlands, researchers can infer what vegetation looked like more than 100,000 years ago.

Large animals kept the landscape open

It therefore seems that Europe was not covered in dense forests before the existence of humanity. But what did the landscape actually look like?

According to the new study’s calculations, between 50 and 75 percent of the landscape was covered in open or semi-open vegetation. And this is probably due to the large mammals that lived at that time, explains Jens-Christian Svenning.

“We know that many large animals lived in Europe at this time. Aurochs, horses, bison, elephants and rhinoceroses. They must have consumed large amounts of plant biomass and thus had the ability to control the growth of trees .” he says and continues:

“Of course, it is also likely that other factors such as flooding and wildfires also played a role. But there is no evidence to suggest that this caused enough disruption. For example, the wildfires Forest encourages pine trees, but most of the time we did not find pine trees as a dominant species.

Although the research group cannot be 100 percent sure of the extent to which large animals were behind the open areas, strong indications suggest that they were. First, large animals like bison have exactly this effect in areas where they are still found in European forests. In addition, beetle fossils from the last interglacial period also show that many large animals lived at that time.

“We looked at a number of beetle fossil finds from this time in the UK. Although there are beetle species that thrive in forests subject to frequent wildfires, we found none in the fossil record. Instead, we found large quantities of dung beetles, showing that parts of the landscape were densely populated with large herbivores,” he says.

Merck’s rhino with pollen between its teeth

There are many indications that large animals maintained the landscape varied before the arrival of humans, with large areas of open and semi-open vegetation.

A very special study carried out in Poland further underlines this theory, explains Jens-Christian Svenning.

“Researchers in Poland took a closer look at Merck rhino fossils to see what this large animal lived on. They found remnants of pollen and twigs between its teeth, and when they analyzed them, they found could see that a large quantity came from hazelnuts,” he says and continues:

“The rhino therefore walked around painfully eating hazel branches and leaves. This supports the theory that large animals affected the vegetation, perhaps just like the historic copses. At the same time, its teeth marks suggest that it fed heavily on grass and sedges throughout its life.

An argument for rewilding

Not only do we need to rewrite the biology books, but the new findings provide new data to support trophic rewilding, that is, the restoration of biodiverse and self-regulated ecosystems through the reestablishment of food web processes, notably through through wild species. megafauna species.

The study results confirm that large animals have a vital role to play in restoration, as Elena Pearce explains.

“Now we know that there was a lot of variation in the landscape. There is every reason to believe that this variation was due to large animals affecting the structure of the vegetation. Many large animals from the interglacial period are now extinct , but we still have bison, horses and oxen,” she says and concludes:

“Without large animals, natural spaces are dominated by dense vegetation, in which many species of plants and butterflies, for example, cannot thrive. It is therefore important to restore large animals to ecosystems if we want to encourage biodiversity.