The American bison reconquers Mexico to fight climate change


The largest terrestrial mammal in America contributes to the regulation of the grasslands of the El Carmen reserve (Coahuila), which accumulate large amounts of carbon

Dozens of American bison graze in the wide open fields of El Carmen (Coahuila), a reserve of 140,000 hectares, almost the same size as Mexico City. The northern plains of the country had forgotten the passage of the mammal, eradicated 100 years ago after decades of indiscriminate hunting and destruction of its habitat. In 2021, and following an initiative led by the Mexican cement company Cemex, the bison returned to roam the grasslands, a soil that accumulates large amounts of carbon, making it key to the fight against climate change. 19 bison arrived at the reserve, and there are already more than 90 in the place. The daily life of the mammal makes it a fundamental actor to regenerate the grass vegetation and to maintain hundreds of species that live with it.

“Evenly pruning the grasses [produced by bison while eating] helps increase the diversity of plants on the land. It also takes care of the regeneration of ecosystems, by taking the seeds from one place to another in its digestive system and defecating them,” explains Rurik List, an Environmental Sciences researcher at the Universidad Autónoma Metropolitana (UAM). The bison is a sober animal, which inadvertently encourages other species to survive in the spaces it inhabits. With its 800 kilograms of weight, it flattens the grass in its wake, an alteration that helps rodents like the prairie dog, which need short grass to watch out for predators.

Cemex carries out different conservation initiatives to try to offset the impact of its operations. The company has more than 250 active quarries around the world, and tries to minimize its footprint from various perspectives: rehabilitating the places that were exploited; preparing them before starting work to protect their biodiversity, and promoting the care of spaces such as the El Carmen reserve, where they arrived 22 years ago. “Since the beginning of the reserve, a series of studies were carried out to determine what was most appropriate. An inventory of flora and fauna was carried out to determine which were the conservation objects to which we had to give retention. And an analysis was made to see the status of the habitat,” says Alejandro Espinosa, director of the El Carmen reserve.

1,000 kilos and a 14 kilometer walk

The bison is a calm animal that walks the fields calmly. It is the largest terrestrial mammal in America: it is more than 1.60 meters tall and can weigh more than 1,000 kilograms. Espinosa is still curious about the animal: “Did you know that a bison can walk up to 14 kilometers a day?” On their long walk, the bison scratch against the trees to relieve the itching of the flies. The hair it releases is used by birds for their nests, which once again contributes to the conservation of other species.

Their passage through the pastures maintains the biodiversity of the area. “They urinate and defecate. When they die, they are 800 kilos of fertilizer that decompose. When they have just died, scavengers also feed on them; and when alive they are occasionally eaten by wolves, more occasionally by grizzly bears, and more occasionally by cougars. They are also a prey species,” List explains.

The director of the American National Bison Association (NBA), Jim Matheson, presents the wild instinct of the American mammal as one of its keys. “Bison have never been domesticated and as such retain innate herding instincts that make them the ideal ruminant for reclaiming North American grasslands,” he explains. The UAM researcher presents the mammal as “an ecologically key species”, with a great effect on the ecosystem in relation to its quantity.

A lung hidden in the plain

Cemex began to rehabilitate the reserve area 22 years ago with the help of environmental authorities, universities, scientists, and with the support of the United States National Park Service. More than two decades later, the landscape is different. “It was rare to see extensive plant cover, there were a lot of rocks, the whole process of overgrazing had just passed. The place was divided into paddocks, with fences. One of the first actions that were carried out was to open up the landscape […] More than 20,000 hectares of grasslands that were invaded by scrub were restored and after several years of work, we realized that it was time for the native species of the area that naturally grazed”,adds Espinosa. Bison were one such methodically selected species. The company tried to choose the specimens that were least crossed with other animals – for their survival they previously reproduced with cattle. The result was 18 bison (three males and 16 females) brought in from other fields in North America.

Grasslands are one of the hidden lungs of the planet. The Food and Agriculture Organization of the United Nations (FAO) argues that these lands allow a greater amount of carbon to be stored and captured than forest ecosystems, capturing up to 30% of the planet’s CO2. To these characteristics, List adds one more: resistance to fires. “90% of the carbon in grasslands is underground. If there is a fire, 10% burns, but 90% remains, which, as soon as the rains arrive, will grow again. Unlike forests such as those in the Redd+ program –dedicated to carbon storage–, whose carbon reserves pass into the atmosphere when burned”, affirms the researcher.

The National Commission of Protected Natural Areas (CONANP) calculates that grasslands can absorb up to 45 tons of carbon per hectare. The 140,000 hectares of the reserve significantly multiply the figure, reaching a theoretical 6.3 million tons.

Scarce in Mexico, iconic in the US

In the Coahuila reserve, the second generation of native offspring of the place was born this year, which gives signs of their settlement. Espinosa has counted, so far, a total of 94 American bison. The CONANP records that in North American territory there were between 30 and 60 million bison 300 years ago, but by 1880, the population was reduced to just over 1,000.

Matheson says that from the IUCN Red List organization, in which they are in charge of determining every five years the possibilities of extinction of different species, they have seen how the bison has remained out of danger. “It has not been threatened with extinction for several years, and the herd has proliferated on all fronts concerned – private, agricultural, tribal and conservation – in recent years. I think the current bison herd is pretty stable, actually,” he says.

The animal whose existence was an important source of food and fur for the native peoples of North America has once again set foot on the lands of northern Mexico. In just two years, its population has grown by more than 60 individuals, and its presence gives a boost to the northern grasslands. “You have bison, you have grasslands; you have grasslands, you have carbon in the soil. You lose the bison and you start to have a range loss,” List concludes.

Source: El Pais