An Elk Island bison. (University of Southampton)

SOUTHAMPTON, United Kingdom — Bringing ice age animals back to combat climate change in the Arctic will not work, a new study says. A team from the University of Southampton say large mammals could not prevent landscapes from changing when temperatures rose thousands of years ago, and they won’t be able to now.

At the end of the last Ice Age 14,000 years ago, the appearance of shrubs dramatically altered the grassy landscapes extending from France across the now-submerged Bering Sea to the Yukon in Canada. Humans often get the blame for this change, as studies point to humans hunting large mammals like the iconic woolly mammoth to extinction — animals that would have kept shrubs in check by trampling over them and helping spread nutrients throughout the soil.

Today, with rising global temperatures, the shrubs are back on the move, spreading even farther north into the colder tundra regions. Reintroducing animals to these parts could possibly reverse the trend, with the added benefit of keeping carbon stored in the ground. However, scientists now have uncovered evidence that suggests climate change, not humans, killed off large animals during the last Ice Age. This mean bringing them back would have little or no effect on rising temps.

“Our study uses a clear predictive test to assess two opposing hypotheses about large animals in ancient and modern tundra ecosystems: that the animals disappeared before the shrubs increased, or that the shrubs increased before the animals disappeared,” says study author Professor Mary Edwards in a media release.

Ancient animals didn’t die out at the hands of humans

The researchers examined fossilized pollen records preserved in lake sediments across Alaska and the Yukon for thousands of years. They were able to accurately pinpoint when shrubs expanded across the region by focusing on fossils within a certain date range.

The team matched this data with the number of bones from horses, bison, mammoths, and moose discovered in the area to provide an estimate of their population size. Willow and birch shrubs began to expand across Alaska and the Yukon around 14,000 years ago, the researchers found. However, the bone records showed that large grazing mammals were still roaming the landscape at that time.

“The results support the idea that at the end of the last ice age a major shift to warmer and wetter conditions transformed the landscape in a way that was highly unfavorable to the animals, including mammoths,” says study lead author Dr. Ali Monteath.

The fate of large mammals like woolly mammoths was therefore sealed by climate change rather than overhunting, the findings suggest.

“While humans may have compounded population declines, our results suggest climate-driven vegetation change was the primary reason the mammals disappeared,” Prof. Edwards adds.

Greenhouse gases will still enter the atmosphere

Bringing back big mammals is therefore unlikely to halt the spread of shrubs and prevent carbon from being released from Arctic permafrost. As soil thaws, microorganisms convert dead plants and other organic material into greenhouse gases like methane, nitrous oxide, and carbon dioxide.

“Rewilding experiments at the scale of local paddocks, as has been done for example at Pleistocene Park (NE Siberia), show that megaherbivores can alter their environment, drive changes in vegetation and even cool soil temperature, but these animal densities are much higher than we would expect for Pleistocene ecosystems. Our study shows that the effect of megafauna grazing is small at sub-continental scales even with the presence of mammoths, and climate, once again, is the main driver of these systems,” says co-author Professor Duane Froese at the University of Alberta.

History suggests high latitude ecosystems like the Arctic may be particularly vulnerable to the effects of climate change.

​​“The hypothesis that reintroducing megafauna will prevent or slow warming-driven permafrost thaw and vegetation change in the Arctic has been bolstered by the idea that Pleistocene megafauna were instrumental in maintaining ice age ecosystems. In contrast to this prediction, our results show that high-latitude ecosystems responded sensitively to past warming events, even though megafauna were abundant on the landscape. These results lend support to the hypothesis that reintroducing megafauna today will do little to desensitize high latitude ecosystems to human driven warming,” explains study co-author Dr. Benjamin Gaglioti of the University of Alaska-Fairbanks.

The findings are published in the journal PNAS.

South West News Service writer Tom Campbell contributed to this report.

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