Tribes and conservation organizations in the United States have recently started bringing the bison back. And scientists studying the returns are discovering that getting the 2,000lb (900kg) grazer back in its native ecosystem could be key to the future of the prairie.
The bison’s biggest service is to assist the prairie in holding onto its water. Bison on the shortgrass prairie send a strong message about the importance of native grazers for landscape resilience. They may offer the prairie a lifeline as climate change tightens its grip.
It takes mettle to live on Montana’s short-grass prairie. It’s dry, windy and a long way from anywhere. In summer, temperatures can top 100F (38C). In winter, the mercury plunges to -50F (-45C). In some spots, it is more than an hour’s drive on gravel roads to buy a loaf of bread (not that bison have to worry about that!).
The indigenous Blackfeet, Nakoda and Gros Ventre peoples successfully adapted to the harsh environment over many centuries. More recently, a handful of hardy white settlers managed it too. Both left their mark on this forbidding land with fire, arrows and the plough. The short-grass prairie makes up 71 million hectares (27,413 sq miles) of remote land straddling the US/Canadian border to the east of the Rocky Mountains. This rare habitat is in ecological decline. For the last 150 years, wildlife have surrendered the prime habitat to cows, and crested wheat-grass, a non-native plant seeded by European settlers for their cattle.
Today, though, parts of the landscape are being shaped by a different resident. This one sports a pair of black horns and a thick cape of curly brown hair. The North American plains bison has a long history here, albeit one that suffered a brutal interruption. For a century and a half, their distinctive humped shoulders and bearded faces were missing from America’s grasslands.
Plains bison co-evolved with the short-grass prairie. In the 12,000 years since the end of the Pleistocene, they have proven themselves to be potent ecosystem engineers. An adult bison eats about 25lb (11kg) of grass a day. The grasses adapted to their foraging. Vegetation across the plains uses the nutrients in their dung. Birds pluck their fur from bushes to insulate their nests.
Bison also shape the land, literally. They roll in the dust and create indentations known as “wallows” that hold water after rainstorms. After the bison move on, insects flourish in these pools, and become a feast for birds and small mammals. Pronghorn antelope survive by following their tracks through deep winter snows. Plains bison spent thousands of years engineering a distinctive grassland ecology from Northern Canada through Montana to Mexico. But more than a century ago, this influence abruptly stopped.
A few decades of slaughter by immigrant settlers led bison numbers to plummet from 60 million to barely 800 living wild in the US and Canada by 1889. Market forces and government policy replaced bison and native people with ranches, white settlement and cattle. For a hundred years, cattle claimed the prairie as their own. But while they were easier to turn into steaks, they were not as finely tuned for prairie life.
I should add here that the elimination of the bison herds by immigrant settlers was also a deliberate American government policy. The concept was to indirectly exterminate the native Indian populations or, at least, drive them onto reservations. The indigenous peoples and the bison were closely intertwined, almost symbiotic, and the government saw eliminating the bison herds as easier way of clearing the land for immigrants.
Today, however, bison are getting a second chance. Tribal reservations are at the forefront of their recovery, taking excess bison from Yellowstone National Park and restoring them to treaty lands. The “American Prairie” organization is also playing a part, buying ranches and returning bison to places where cattle were once king. About 30,000 bison now exist in conservation herds in various parks and protected areas across the country.
Although rivers and streams cover less than 2% of the prairie, they are crucial refuges for its wildlife. A study shows increases in vegetation and bird diversity on creeks where bison have replaced cattle. The study also found more deer and elk. Other studies show that year-round, low-density grazing by bison is associated with more variety in woody vegetation heights and more native plant diversity in riparian areas than seasonal grazing by cattle. Well-vegetated creeks are the prairie’s lifeblood. They keep the soil moist, the vegetation green, and they provide dispersal corridors for large mammals like mountain lions and black bears. One day, they may provide safe passage for recovering grizzly bears.
Conservationists often tout the benefits of bringing back top predators to restore balance to ecosystems. The importance of bringing back large, native grazers is lesser known but equally important. In Kansas, 30 years of bison grazing in tall-grass prairie has been shown to increase native plant species richness. In Europe, it is hoped the restoration of European bison in Kent in the UK will do something similar for ancient woodlands. Across the world, native grazers are ready to slip back into ecosystems to resume their lost roles, if we have enough intelligence and foresight to let them…..and even encourage them.
