Bison are already iconic, but new research also looks at their role in carbon storage

Bison are so iconic that in 2016, they became the official mammal of the United States, but the bovids may also be good for the environment because of the species’ role in the carbon cycle.

A report from the Yale School of the Environment found that bison reintroduced in the Carpathian region of Romania could boost the ecosystem’s ability to take up carbon. The report estimated that bison caused the ecosystem to take up about 9.8 times more carbon than it would have in the species’ absence.

“Animals, in some cases, can actually boost the ecosystem’s ability to capture carbon through photosynthesis, and then store it in the ecosystem,” Oswald Schmitz, the report’s lead author and a professor of population and community ecology, said in an interview.

Organizations like the United Nations are aiming to reach net zero carbon emissions by 2050 to avoid global temperature rise, so there have been many efforts to reduce carbon emissions and to study capturing and storing carbon that is already in the atmosphere. Schmitz believes that, along with reducing fossil fuel emissions, animal conservation and nature-based solutions could help avoid a global temperature rise.

In an earlier study, Schmitz also looked at the role American bison play in the carbon cycle. That research found more of a doubling or tripling effect than a 9.8 times boost.

Bison increase carbon storage in an ecosystem by helping grass flourish.

“When bison graze vegetation, like grass, it stimulates the grass to grow more heartily and vigorously. ... Because it’s flourishing more when it’s grazed, it takes up more carbon,” Schmitz said.

Then the bison release nutrients from the grasses they eat in dung and urine, which fertilizes the soil.

“It’s a one-two punch that the animals do. They eat and stimulate the plants to grow and at the same time, they’re fertilizing, quickly fertilizing that vegetation to stimulate more growth, and through the more growth you get more carbon uptake,” Schmitz said.

Bison also trample, reducing microbial activity and root respiration, causing less CO² loss.

People studying earth systems, doing climate modeling and considering nature-based solutions haven’t always appreciated the role that animals play, Schmitz said.

“What people have historically assumed is that animals aren’t abundant enough to really have a huge effect on the carbon cycle, but this all just assumes that you’re only accounting for the carbon stored in their bodies,” Schmitz said.

His research has focused on the feedback loop that animals, including bison, can cause to help an environment flourish and reduce CO² loss. The research could help support existing animal conservation efforts, including efforts to help the American bison.

In New Mexico, bison conservation efforts have been ongoing for years. One of those efforts is on three Ted Turner Ranches. The Ladder and Armendaris ranches are in southern New Mexico, while the Vermejo Ranch is to the north, where the bison have500,000 acres to graze on. As of recently, there were 1,646 bison on Vermejo, approximately 900 on Ladder Ranch and 650 on Armendaris.

Historically, on short grass prairies in New Mexico bison were likely living on a consistent basis, while in desert areas in southern New Mexico bison likely were more transitory, said Carter Kruse, who oversees the Turner Institute of Ecoagriculture. Bison are native grazers in New Mexico and across the Great Plains, so managing the species is pretty easy, Kruse said. The key is keeping the bison moving to different areas so that the plant vigor isn’t impacted by their grazing.

Bison are an iconic species in the American imagination

“Even though we have large ranches, they’re still small by bison’s perspective. They used to run over thousands of miles or hundreds of miles, certainly. So we try to move them around on the property so that they’re most efficiently using the forage ... and not overusing forage in a way that’s detrimental to developing the plant community or the soil health,” Kruse said.

Why not cows?

Schmitz is often asked, “Well, can’t cattle do the same thing as bison?” According to Schmitz, cattle can, but bison have more of an impact at lower numbers.

One difference comes down to anatomy. Bison have wide muzzles with flat and wide mouths, while cattle tend to have pointier muzzles and are more selective in their choice of foods, he said.

“Whereas the bison, they stick their head down, and they just mow. They just move across the landscape and eat everything in sight and keep it nice and low and mow ... where with cattle, you can sometimes get a more patchy environment,” Schmitz said.

To get the same mowing effect with cattle, the bovids would need to be stocked in much higher densities, Schmitz said, which can also contribute to methane release and overgrazing.