It’s a delicate balance though, and Schmitz points out that different ecosystems can actually benefit from having more large herbivores. Grey wolves that predate on elk in the North American grasslands, for example, can reduce the amount of carbon those landscapes can hold. Elk faeces can fertilise the soil and stimulate the growth of grass. In ecosystems where wildfires are not common, more vegetation can be a store of carbon.
And this is often where the complexity lies. One animal has a beneficial effect on the climate in one ecosystem may not in another. Yet they also play a crucial role in both.
In the Arctic, Musk oxen are a favoured prey of wolves, yet these large herbivores have a “huge influence” in tackling climate change by protecting the frozen soil, says Schmitz. “By grazing and trampling they protect against permafrost thawing,” he says. “If permafrost thaws, it can release many millions to billions of tonnes of methane.” Methane is a potent greenhouse gas.
These complex relationships are one reason why Christopher Sandom, a rewilding expert and biology lecturer at the University of Sussex, UK, warns that replenishing animal populations will not be a silver bullet for climate change. “Research has shown that nature is a complex set of interlocking processes that may not give you the expected outcome,” he says. “Rewilding cannot be seen as a panacea. We must not simply think that nature can suck all the carbon up and not adopt measures across the board to reduce man-made emissions.”
But he adds that it is clear that animals and their conservation need to be included in the discussions around climate change. “Planting trees is indeed important, but nature shows they need animals to help them grow,” he says.