Rewilding and Climate Change

by Belinda Recio

On January 12, 1995, eight gray wolves from Jasper National Park in Alberta, Canada, were released into Yellowstone National Park. Wolves hadn’t lived in Yellowstone since the 1920s, when they were eradicated as a result of being hunted, trapped and poisoned by humans. In the years that followed the relocation, the Yellowstone wolf population slowly increased, which scientists expected. What they didn’t expect was the extent to which the wolves would change the ecosystem and landscape. 

The wolves preyed upon elk, so the elk population stabilized. The wolves also killed coyotes, which resulted in larger populations of rabbits and mice—prey not only for coyotes, but also for badgers, foxes, hawks and other small predators whose numbers increased. As Yellowstone’s ecosystem changed, so did its physical geography. Because fewer elk were browsing, willow and aspen groves returned, which created better habitat for beavers, whose dams slowed the flow of streams and restored wetland vegetation. This, in turn, provided habitats for other animals, such as ducks, fish, otters and muskrats. 

Returning species to their original habitat is known as “rewilding.” The Yellowstone wolves are the best-known example of rewilding, and demonstrate how every member of an ecosystem is critical to its ecological balance and even its physical geography. The story of the Yellowstone wolves has inspired some scientists to wonder if rewilding could play a role in mitigating the effects of climate change. 

Until roughly 12 million years ago, herds of large herbivorous animals roamed the grasslands of the Arctic tundra, where they suppressed the growth of trees and shrubs by eating or trampling saplings. Keeping these dark, sun-absorbing leafy plants to a minimum allowed the grasslands to thrive. Grasslands reflect most sunlight, and are colder than land covered in shrubs and trees, which absorb more sunlight. The soil under grasslands freezes deeper and stays frozen longer than land covered in leafy plants.

Based on fossil records, scientists estimate that in the Pleistocene Era, which ended about 12 million years ago, each square mile of the Arctic was home to roughly 15 reindeer, 7.5 horses, five bison and one woolly mammoth. Compared to present populations, that was a lot of large herbivores keeping trees and shrubs to a minimum. Based on the significant difference in herbivore density between the Pleistocene and the present—as well as fossil records that indicate that Arctic was once covered in more grasslands—scientists developed the idea of “Megafaunal Ecosystem Engineering.” This rewilding concept proposes to bring large herbivores back to the Arctic to restore the ancient Arctic “mammoth steppe” ecosystem, and slow global warming. 

Megafaunal Ecosystem Engineering posits that repopulating the Arctic with large herbivores—such as bison and horses—could slow the thawing of the permafrost, thereby reducing the release of greenhouse gases trapped in the frozen ground. Some scientists have even suggested trying to resurrect the Wooly Mammoth from extinction for this purpose. They propose that splicing DNA from Asian elephants with Wooly 

Mammoth DNA could produce viable embryos. But this controversial idea raises all kinds of ethical, biological and ecological concerns, and most scientists agree that large extant herbivores are much better choices. 

If the idea works as envisioned, bison, horses, reindeer and other large herbivores would keep the shrubs and trees to a minimum and grasslands would thrive, protecting the permafrost. Dr. Marc Macias-Fauria of the University of Oxford believes that the carbon emissions from thawing permafrost could be as much as 4.35 billion tons per year over the 21st century. This is about half as much as the carbon released by global fossil fuel emissions. If Megafaunal Ecosystem Engineering could stop or even just slow the emissions from thawing permafrost, scientists would have more time to develop new technologies to reduce the human production of greenhouse gases. 

In 1996, a group of Russian scientists decided to test the idea of Megafaunal Ecosystem Engineering by creating Pleistocene Park, a 144 square kilometer area in northeastern Siberia. They introduced native animals, such as Yakutian horses, moose and reindeer, as well as animals from other ecosystems, such as musk ox, bison and yaks. Twenty years later, the herbivorous megafauna had converted parts of the park to grasslands and had increased carbon storage in the soil. The scientists acknowledge that there is still much more research to do, but they consider the initial results promising. 

Rewilding—whether by returning wolves to Yellowstone or repopulating the Arctic with herbivorous megafauna—offers the hopeful thought that nature herself might offer us the very solutions we need to restore balance and health to ecosystems and perhaps even the entire planet. 


BELINDA RECIO, recipient of the Humane Society’s Award for Innovation in the Study of Animals, owns True North Gallery (truenorthgallery.net) in Hamilton, Massachusetts, where she exhibits art that connects people with animals and the natural world. 

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