It has been claimed that in the past, Britain was covered by such thick and unbroken forest that a squirrel would have been able to travel the length of the island without ever touching the ground. But a study of ancient pollen indicates that the natural state of Europe’s forests was far more varied, with lots of grassland and light woodland as well as the dark, dense forests of popular imagination.
“On average, in each place that we looked at, over half the vegetation was open or light woodland. Imagine a kind of savannah landscape,” says Elena Pearce at Aarhus University in Denmark.
This is probably due to megafauna including straight-tusked elephants and rhinoceros, she says, since they suppress woody vegetation by eating and trampling young trees.
Almost all previous studies have looked at the 10,000 years or so since the last glacial period. By this time humans were already a dominant factor in shaping the landscape. So Pearce and her colleagues looked back much further, to the previous interglacial period around 115,000 to 130,000 years ago.
Her team analysed nearly 100 pollen samples from this time from locations across Europe, from the Arctic to the Mediterranean. Pollen preserved in lake sediments shows what plants were present in an area, but can give a misleading picture of past vegetation, because trees typically produce far more pollen than grasses.
Pearce and her colleagues used a computer model developed by other groups that takes account of factors such as how much pollen different species produce to predict vegetation cover. This model has been checked using modern pollen samples.
The team found past vegetation varied greatly both in geographic area and over time. This variability could not be explained by climatic factors, they found. Nor was it mainly due to fires, with far fewer fires at this time than after the arrival of modern humans.
That leaves megafauna as the most likely explanation, Pearce says, although her team couldn’t test this idea directly. “I think megafauna is the leading factor.”
Pearce says fossil evidence of the kind of mammals living in Europe before humans arrived has long pointed to a more open landscape. But the orthodoxy based on the abundance of tree pollen has been that it was mostly closed-canopy forest. Her study resolves this apparent mismatch between the pollen record and the faunal record for the first time.
She thinks conservationists should aim to recreate the processes that created this past landscape, rather than trying to recreate the landscape itself. For instance, animals such as wild boars that dig up the ground help prevent species such as stinging nettles becoming dominant.
“They’re basically just messy, and all that mess creates brilliant habitats for things to thrive in,” says Pearce.