A keystone species, bison once roamed the American Great Plains in the tens of millions, but were hunted to near extinction.

Bison are known as ecosystem engineers because they perform many services for the habitats in which they live, like rolling around and packing down soil in wallows that collect rainwater and grazing on different heights of grasses, which provide birds with nesting grounds.

A new study by researchers from Yale University and Memorial University of Newfoundland has found that a herd of 170 bison being reintroduced to the Țarcu mountains of Romania could help sequester carbon dioxide emissions equal to removing at least 43,000 gas-powered cars from United States roads for one year, reported The Guardian.

“Most carbon cycle models do not consider animal-mediated effects, focusing instead on carbon exchanges among plants, microbes, and the atmosphere. Yet, a growing body of empirical evidence from diverse ecosystems points to pervasive animal effects on ecosystem carbon cycling and shows that ignoring them could lead to misrepresentation of an ecosystem’s carbon cycle,” the study said.

More than two centuries ago, Romania lost its last European bison. However, in 2014 the species was reintroduced to the Carpathian mountains by WWF Romania and Rewilding Europe, The Guardian reported. The 100 who were brought to the Tarcu mountains have grown to more than 170 — one of the biggest free-roaming bison populations on the European continent. The landscape can accommodate as many as 350 to 450 individuals.

For the study, the researchers used a model developed at the Yale School for the Environment. It calculates how much atmospheric carbon wildlife assists in capturing and storing in soils through their ecosystem interactions.

“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,” said professor Oswald Schmitz, lead author of the study and a professor of population and community ecology at Yale University, as reported by The Guardian.

The herd of 170 graze in a grasslands area of nearly 19.3 square miles inside the wider Țarcu mountain range. The research team found that the bison could potentially capture another 59,525 tons of carbon annually.

The team said the number corresponds with the amount of annual carbon dioxide released by an average of at least 43,000 gas-powered cars in the U.S., or 123,000 in Europe, due to their increased energy efficiency.

“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,” Schmitz said.

When bison browse and graze, it helps with the maintenance of a biodiverse landscape of scrub, grasslands, forests and microhabitats.

Their return to the Țarcu has inspired eco-businesses and tourism centered around rewilding.

Schmitz explained that the climate and soil conditions of the Carpathian mountain grasslands are specific, so bison’s impacts might not be the same in other locations around the world, such as prairies in the U.S., which are much less productive.

“This research opens up a whole new raft of options for climate policymakers around the world. 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,” said Magnus Sylvén, Global Rewilding Alliance’s director of science policy practice, as The Guardian reported.

The team explored the details of nine species — including sea otters, musk oxen and tropical forest elephants — and have started looking into others.

“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,” Schmitz said, as reported by The Guardian.

The study, “Rewiring the Carbon Cycle: A Theoretical Framework for Animal-Driven Ecosystem Carbon Sequestration,” was published in the journal JGR Biogeosciences.

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