June 16, 2024

A herd of 170 bison reintroduced to Romania’s Țarcu mountains could help store CO2 emissions equivalent to removing 43,000 US cars from the road for a year, research has found, demonstrating how the animals can help mitigate some effects of the climate crisis.

European bison disappeared from Romania more than 200 years ago, but Rewilding Europe and WWF Romania reintroduced the species to the southern Carpathian mountains in 2014. Since then, more than 100 bison have been given new homes in the Țarcu mountains, growing to more than 170 animals today, one of the largest free-roaming populations in Europe. The landscape holds the potential for 350-450 bison.

The latest research, which has not been peer-reviewed, used a new model developed by scientists at the Yale School of the Environment and funded by the Global Rewilding Alliance, with the bison paper funded by WWF Netherlands. The model, which has been published and peer reviewed in the Journal of Geophysical Research: Biogeosciences, calculates the additional amount of atmospheric CO2 that wildlife species help to capture and store in soils through their interactions within ecosystems.

The European bison herd grazing in an area of nearly 50 sq km of grasslands within the wider Țarcu mountains was found to potentially capture an additional 54,000 tonnes of carbon a year. That is nearly 9.8 times more carbon than without the bison – although the report authors noted the 9.8 figure could be up to 55% higher or lower, so making the median estimate uncertain. This corresponds to the yearly CO2 released by a median of 43,000 average US petrol cars, or 84,000 using the higher figure, or a median of 123,000 average European cars, due to their higher energy efficiency, the researchers said.

Prof Oswald Schmitz of the Yale School of the Environment in Connecticut in the US, who was the lead author of the report, said: “Bison influence grassland and forest ecosystems by grazing grasslands evenly, recycling nutrients to fertilise the soil and all of its life, dispersing seeds to enrich the ecosystem, and compacting the soil to prevent stored carbon from being released.

Bison grazing recycles nutrients to fertilise the soil, dispersing seeds, and compacting the soil to prevent stored carbon dioxide from being released. Photograph: Daniel Mirlea/WWF Romania

“These creatures evolved for millions of years with grassland and forest ecosystems, and their removal, especially where grasslands have been ploughed up, has led to the release of vast amounts of carbon. Restoring these ecosystems can bring back balance, and ‘rewilded’ bison are some of the climate heroes that can help achieve this.”

Alexander Lees, a reader in biodiversity at Manchester Metropolitan University, who was not involved with the study, said it “makes a convincing case for European bison reintroduction as a nature-based climate solution – one with major biodiversity conservation co-benefits”.

Lees said more in-the-field research would help validate the models and assist understanding of how long it would take for bison benefits to accrue, adding: “This study reinforces an emerging consensus that large mammals have very important roles in the carbon cycle. Rewilding efforts, including, where appropriate, reintroductions, represent key tools in tackling the intertwined biodiversity and climate crises.”

A keystone species, bison play an important role in ecosystems – their grazing and browsing helps maintain a biodiverse landscape of forests, scrub, grasslands and microhabitats. In the Țarcu mountains, their return has also inspired nature-based tourism and businesses around rewilding. Schmitz noted that the Carpathian grasslands have specific soil and climate conditions, so the effect of the European bison could not necessarily be extrapolated internationally – American prairies, for example, have much lower productivity.

Bison might be just one of several large mammals that have an important role to play in the carbon cycle. Photograph: Alexander Turner/The Guardian

“This research opens up a whole new raft of options for climate policymakers around the world,” said Magnus Sylvén, the director of science policy practice at Global Rewilding Alliance. “Until now, nature protection and restoration has largely been treated as another challenge and cost that we need to face alongside the climate emergency. This research shows we can address both challenges: we can bring back nature through rewilding and this will draw down vast amounts of carbon, helping to stabilise the global climate.”

The report on Romania’s European bison is “the first of its kind”, said Sylvén, adding that the model provided “a very powerful tool at hand to give directions to wildlife reintroductions”.

Schmitz said the team had looked at nine species in detail, including tropical forest elephants, musk oxen and sea otters, and had begun to investigate others. He added: “Many of them show similar promise to these bison, often doubling an ecosystem’s capacity to draw down and store carbon, and sometimes much more. This really is a policy option with massive potential.”

This headline and article were amended on 16 May 2024. Due to an error in the original research, a previous version stated that Carpathian ecosystems browsed by bison could store 2m tonnes of carbon, equivalent to the emissions of 1.88m average US cars petrol a year. The research authors have since retracted these figures, which were due to a coding error. The correct figure is that bison could store 54,000 tonnes of carbon, equivalent to the emissions of 43,000 average US petrol cars.

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