Africa’s megaherbivores — elephants, rhinos and hippos — could potentially play a major role in mitigating climate change, says Professor Graham Kerley, director of the Centre for African Conservation Ecology at Nelson Mandela University.
He is one of six authors of a paper published in October in the journal Philosophical Transactions. Titled “Trophic rewilding as a climate mitigation strategy?” the paper was co-authored by Kerley and researchers from Sweden, SA, the Netherlands and New Mexico.
“The Nobel prize for economics has just been awarded to people who work on climate change as it is the biggest threat facing society. Far bigger than global terrorism, it will affect everyone,” he says. “This study looks at an area that has not been addressed previously: the role of large and megaherbivores in mitigating climate change.”
The study emanated from speculative discussions between scientists and proposes using Africa as a living laboratory to understand how these animals influence the landscape and climate.
“Megaherbivore communities globally have significantly changed over the last 15,000 to 20,000 years,” Kerley explains. “Before then, the world was dominated by megaherbivores, but North America, South America and most of Eurasia have lost all theirs, including the mammoth, mastodon, gomphothere (four-tusk elephant), giant ground sloth and woolly rhinoceros.
“This is a very recent extinction and the consequences have been profound in terms of how the climate has shifted due to the large-scale loss of megaherbivores worldwide. Megaherbivores, hind gut fermenters that produce far less methane, have since largely been replaced with livestock — particularly sheep and cattle — that produce far more methane.
“Today, we define a megaherbivore as an animal weighing over 1,000kg. The prehistoric megaherbivores were far larger and heavier than the megaherbivores of today still found in Africa. In SA, megaherbivores occurred just about everywhere except very dry areas like the Kalahari, and the hippos would have inhabited the water course areas.”
Some scientists believe that the reason why only Africa retained its megaherbivores in sizeable numbers is because they evolved alongside the first human populations. The African animals were therefore more alert to human hunting, they speculate, and more naïve and easy prey on other continents when humans arrived there.
With their lengthy gestation periods and slow growth, reproduction by megaherbivores could not keep up with the assault. In Africa, conservation initiatives were put in place before the megaherbivores were hunted to extinction, but the current poaching onslaught is expected to reverse the recent growth in their numbers.
The effect on the global climate as a result of the mass loss of megaherbivores in other parts of the world is finally being understood, and is explained in the paper in terms of their contribution to climate change mitigation.
The mega browsers — in Africa these are the black rhino and elephant — help to maintain the balance in savanna systems between trees and grasslands, working in synergy with the mega grazers, Kerley explains. Without the mega browsers, trees and bushes would take over the grasslands, and without the them, grasslands would take over the tree and forest areas.
“The importance of vast areas of grassland, in addition to their role as water production areas, is that they reflect the sunshine, and therefore reduce solar radiation.
“This might prove to be even more important in keeping the planet cool than dark areas, such as trees and forests which absorb heat and carbon and play an important role in carbon sequestration (long-term carbon storage).
“The megaherbivores also play a major role in nutrient recycling, soil health and seed dispersal. Elephants, for example, contribute to the dispersal of the seeds for hardwood trees and are therefore essential to the growth of hardwoods that grow slowly and hold their carbon for long periods.”
The authors of the paper emphasise that the megaherbivore proposition is not a single solution, but a contribution to the climate change mitigation strategy.
“The latest report from the Intergovernmental Panel on Climate Change states that we have to do a lot more to keep the world from warming by more than 1.5°C and to reverse the changes to the atmosphere in order to avoid catastrophic climate consequences, including large-scale extinction,” says Kerley.
He refers to an article in The Conservation Africa on October 10 by systems ecologist Professor Robert Scholes from Wits University’s Global Change Institute, who writes: “It seems inevitable that the planet will overshoot the 1.5°C global mark, and probably also the 2°C mark. Cooling the atmosphere later in the century would require the removal of up to a trillion tons of carbon dioxide.
“The world doesn’t yet have affordable, proven technology to do this at the required scale. The approach that is most commonly punted — mass tree-planting — is a non-starter in most of southern Africa, where the arable land and water resources are needed for food production, and the marginal land is too dry to grow forests.”
The potential of megaherbivores to mitigate climate change raises the interesting discussion of what it would mean to reintroduce them into Eurasia, North America and South America where they have been driven into extinction by humans.
“We need to do far more research into this, with many questions to be answered. These include: if you have an equal biomass of elephants and cattle, what happens to respective landscapes when you have systems dominated by megaherbivores and wildlife versus systems dominated by domestic livestock?” Kerley says.
“What are the implications for climate mitigation, land use and food security? Will the world need to create larger areas for megaherbivores and other wildlife? How are we managing our wildlife for climate change mitigation? What are the consequences of not having megaherbivores?
“If megaherbivores do play a significant role in climate change mitigation, Africa could play a major environmental and economic role in making them available to the rest of the world. Would the world be open to this, are we ready for this?
“All these ideas and questions are somewhat speculative, but we need to explore them, and, as a matter of great urgency, come up with new, large-scale, innovative climate mitigation strategies.”