Before European settlers came to North America, bison migrations were essential to the annual renewal of shortgrass prairie ecosystems, says EarthWatch chief scientist Cristina Eisenberg. By nipping off grasses, fixing nitrogen in the soil, and churning up the earth, their passage kept grasslands across parts of Montana, Wyoming, Colorado and Idaho functioning smoothly.
Equally important was fire, which led to spikes in plant productivity, and wolves, which controlled bison and elk populations. Eisenberg calls bison, wolves and fire the “keystone forces of nature” — the three legs of a stool that prop up a vast array of plants and animals in grassland ecosystems. Of course, she adds ruefully, European settlers found all three of these important forces “terribly inconvenient” and spent centuries trying to wipe them from the landscape.
Now, we’ve come full circle: Land managers in many protected places — from Yellowstone to Rocky Mountain National Park to Waterton Lakes National Park in Alberta, just over the Canadian border from Glacier — are trying to rectify decades of misguided policy by reintroducing one or more of the stool’s three legs. Eisenberg has just one question for them: “Is this even working?”
In other words, is it possible to rewild a place without all three legs in place? To answer that question, Eisenberg is conducting research in both Waterton Lakes, where there are wolves and controlled fire but no free-ranging bison, and on land owned by the Blackfeet Nation just outside the park, where the tribe is interested in bringing bison back. By collecting baseline data and comparing restoration efforts in both places, Eisenberg hopes to answer basic questions about shortgrass prairies — How often did they burn? How many bison are enough? — that could guide land managers elsewhere in the West struggling return grasslands to a more natural condition.
“We’re trying to re-wild North America with mixed success,” says Eisenberg, who raised her family on 20 acres in northwest Montana and now works primarily as a research scientist. “It’s like trying to fix a watch and you’re missing one of the critical pieces. It might work for a while, but it’ll keep breaking and you’ll keep having to fix it.”
In Waterton Lakes, for instance, aspens are encroaching onto the shortgrass prairie. Only 3 percent of Canada’s shortgrass prairie remains, so park managers are particularly keen to conserve what’s left. The obvious solution seemed to be controlled burns — studies in Rocky Mountain National Park and elsewhere have shown that elk browse aspen shoots so heavily after a fire that they knock back aspen, making room for grasses to grow.
But that hasn’t happened in Waterton. Eisenberg suspects it has to do with the presence of wolves, which were absent from the previous study sites. “Instead of browsing the aspen sprouts, the elk are avoiding them, because there’s all this stuff on the ground that makes it hard for them to run away if a wolf is chasing them,” she hypothesizes.
A more holistic solution, Eisenberg thinks, would be to bring back free-roaming bison, which suppress woody regrowth by trampling and digging it up with their horns. But that’s controversial with local ranchers. So Eisenberg is working with the Blackfoot on nearby tribal land to conduct mirror-image studies to those inside the park. The joint studies are funded through 2020 by EarthWatch, the Blackfoot and Parks Canada. Her work is still in it’s relatively early stages, but eventually, when bison return to tribal lands, she hopes to have all the pieces in place to track their effect on biodiversity, plant productivity and other measures of ecosystem renewal. “None of these things is a silver bullet alone,” she says. “In order to fix the ecological problems we’ve created, you don’t just put back something you took out without understanding how it’s going to affect everything else.”
I asked Eisenberg if it makes sense, in today’s world, to attempt to restore environments to some idealized pre-contact state. She thinks it does. Any one of the stool’s legs increases biodiversity wherever it occurs, she said. “And when they occur together, it’s unbelievable what happens in terms of species diversity.” In the face of climate change, that increased biodiversity may be the best form of insurance against extinction.
Krista Langlois is a correspondent for High Country News. Follow @cestmoiLanglois