New study identifies best areas for rewilding European bison

At the end of the last ice age, large herds of bison roamed Europe. But by 1927, the European bison had disappeared in the wild, with only about 60 individuals remaining in captivity. Scientists have long debated the exact causes of the near-extinction of grazers and whether humans are to blame.

A new study combines fossil evidence, ancient DNA and modeling to unravel the threats that have driven the decline of Europe’s bison population. Rapid environmental change and hunting by humans are the main factors, according to the study published in the journal. Proceedings of the Royal Society B: Biological Sciences.

Since the near extinction of the European bison, enormous conservation efforts have helped restore wild populations, and their numbers are increasing. However, the study authors argue that ensuring the long-term protection and recovery of the species requires understanding why it nearly went extinct in the first place.

“Our study also suggests areas where rewilding attempts are most likely to succeed,” said lead author July Pilowsky, currently a disease ecologist at the Cary Institute of Ecosystem Studies. Pilowsky completed his research while working on his Ph.D. at the University of Adelaide and the University of Copenhagen.

Reconstructing the decline of the bison

“This study is one of the rare attempts to reconstruct the process of species extinction,” explained co-author Rafał Kowalczyk, who heads the Institute for Mammal Research at the Polish Academy of Sciences. “This is the fascinating story of a species that is the last remnant of the legendary megafauna that inhabited the European continent in the late Pleistocene, and a lesson in how easily a species can be wiped out.”

To clarify the factors that led to the decline of the European bison, Pilowsky and his colleagues constructed a detailed simulation combining paleoclimate data, vegetation and habitat information, human population growth and expansion of the Paleolithic across Eurasia, as well as the population dynamics and dispersal of bison. Historical records, fossil evidence and ancient DNA were used to independently test the accuracy of the model.

The researchers ran 55,000 different simulations to explore how climate, human hunting and land use change affected the population and distribution of bison across Europe. Turning off different variables one by one allowed the scientists to test the importance of each variable.

If, for example, human destruction of forests was reduced to zero, and there was no change in the abundance and range of bison, then scientists would conclude that the change in Land use was probably not a factor in the species’ disappearance.

After reconstructing 21,000 years of European bison range dynamics, the team concluded that the bison range began to collapse around 14,700 years ago due to warming rapid climate change and its effects on bison habitat. Subsequently, the activities of increasing numbers of humans prevented the bison from rebounding. Hunting has caused range loss in the north and east of its range, while land-use change has been responsible for losses in the west and south. The arrival of firearms in the 1500s greatly accelerated the decline of the species.

“Stories of the past repeat themselves in the present,” Kowalczyk said. Land use change, poaching and climate change are exactly the same threats that endanger the European bison today. “Learning lessons from the past and understanding the process of species extinction can help us better protect species.”

Maximize conservation efforts

The European bison is a priority species for conservation because it plays an important role as an ecosystem engineer, restoring grassland habitat. Thanks to efforts to recover and rewild the species, today there are approximately 7,300 European bison in the wild. However, rewilding was carried out without a good understanding of the habitats and regions where bison once thrived.

As a result, the species has been released in sites ranging from the coastal dunes of the Netherlands to the mountains of the French Alps and the Mediterranean climate of Spain, with mixed success. Of the 47 free-living populations of European bison, only eight have more than 150 adults, and all rely on supplemental feeding due to poor habitat quality.

By identifying areas where European bison would be distributed today if hunting and land use change had not occurred, the study focuses on regions most suitable for reintroduction of the species. These include parts of Poland, Ukraine and western Russia.

With habitat restoration, parts of the Balkans and Germany could also become good sites for bison reintroduction.

“I hope the maps we produced can help inform future efforts in terms of where reintroduction efforts should take place,” Pilowsky said. “This is especially crucial because of the war in Ukraine. More than 50 percent of all free-ranging bison are in Ukraine, and conservationists are really concerned.”

Next steps

Pilowsky then hopes to adjust the simulations to identify sites that are suitable not only for European bison today, but also in the future under human-caused climate and environmental changes.

The study methodology could also be adapted to reconstruct the causes of population declines and range collapses of other large herbivores, including American bison, to increase awareness of past threats and enrich current conservation plans.

The lessons learned illuminate new lines of inquiry for Pilowsky. At the Cary Institute, they are translating bison simulation code into new software that models disease transmission in wildlife.

“I literally have my bison code open on one monitor and my new code that I’m building on another monitor,” they said. Instead of simulating the abundance and range of bison, the new software shows the prevalence and distribution of a disease in a species over time.