US scientists plan to reintroduce wildlife missing for 13,000 years 

The Bolson tortoise's release will be the first step in a re-wilding project.

Later this year, several giant Bolson tortoises will be taken from a facility in Arizona to the 63,000ha Ladder Ranch in New Mexico. If the tortoise adapts to its new home it will be the first step in a controversial "re-wilding" project to create a vast "ecological history park" filled with creatures from the Late Pleistocene era on the Great Plains of North America.

The tortoise, extinct in the United States for 8000 years, lives in Mexico's Chihuahua Desert. The plan has turned the world of conservation biology upside down and if successful it could have profound implications for global conservation.

In 1805, when explorers Meriwether Lewis and William Clark made their epic journey through the American West, the prairies teemed with large animals, from buffalo that trampled their campsite, to elk, wolves, mountain lions and grizzly bears.

Yet fossil records show this was merely the rump of a much greater megafauna (large vertebrates) population, which included lions, mammoths, mastodons, cheetahs, horses and camels that had vanished many millennia before humans arrived.

But what if these animals, still found elsewhere with the exception of the proboscidians (elephant), returned to the Americas?

Several scientists, writing in Nature, have proposed just that. Instead of using 1492, when Columbus arrived, as a restoration benchmark, Re-wilding North America advocated pushing the clock back 13,000 years to create "an alternative vision of 21st-century conservation biology".

Its authors say that the gradual release of large vertebrates, as proxies for Pleistocene species, into the US southwest and the Great Plains, would revitalise threatened ecosystems and boost depressed economies. Given threats to megafauna elsewhere, its supporters believe "re-wilding of American sites carries global conservation implications".

Echoes of the Pleistocene, which ended 10,000 years ago, still linger in the US. Pronghorn antelopes can run up to 112km/h, far faster than predators. "Almost everything about pronghorn biology screams cheetah," says Josh Donlan, an evolutionary biologist who co-authored the Nature paper.

"That's the result of cheetahs preying on American grasslands for 4 million years." In a re-wilded range cheetahs will chase, kill and eat pronghorns. "That's what being a cheetah is all about. People would probably pay money to see it."

The public reaction to this bold idea was immediate and not always complimentary. "Re-wilding the plains is a bit too wild," cautioned the Kansas City Star, musing about the quality of fence needed to separate people from, say, lions and elephants, the last of the proboscidians.

As for the economic benefits that re-wilding might bestow on the Great Plains - increasingly depopulated and littered by ghost towns - the Chicago Tribune recalled a 1989 Buffalo Commons proposal by academics Frank and Deborah Popper. The Poppers felt bison herds would resuscitate the Prairies as a tourist-friendly US Serengeti. This provoked an outcry from inhabitants more used to "taming" nature.

The decade-old Yellowstone wolf restoration project, which has created a wild wolf population numbering some 900, still needs federal protection from vengeful locals.

Responses to the Nature idea echoed the outcry against the wolves and the Poppers. "I received more than 1000 emails," says Donlan. "more than half hated the idea."

Time may be on Donlan's side. Raising buffalo is a growth industry out West, and thousands roam ranches and Indian land.

Scientists were also divided. Some feared re-wilding North America would drain money - and animals - from African projects. Others blasted the plan as junk science.

"Essentially, you'd be running it like a zoo," Eric Dinerstein, the World Wildlife Fund's top scientist told National Geographic. "Why not just encourage Disney to run a theme park?"

"It is clear this idea rattled the cage of the scientific community and stirred the public," says Donlan. He envisages a softly, softly campaign of extensive research guided by the fossil record.

It is unsure, for example, how Pleistocene proxies would handle America's climate extremes. Mitochondria DNA shows that the American "cheetah", Miracinonyx trumani, evolved separately from its African namesake. Reintroduced species from captive stock would be released on fenced private land long before lions or elephants.

Given Washington's anti-environmental tone, initial support will come from sources such as the Turner Endangered Species Fund, which is funding the Bolson tortoise project, re-wilding's pilot scheme.

"If this works everyone will catch the Bolson tortoise bug and there will be restoration sites all over the Southwest," says Mike Phillips, executive director at the species fund, which is being bankrolled by media tycoon and conservationist Ted Turner.

Meddling in nature is inherently risky, but re-wilding is arguably no more so than the ecological consequences of wiping out Pleistocene megafauna. Evidence suggests top-down predators maintain the diversity of ecosystems and wildlife.

Wolves were reintroduced to Yellowstone to cull ungulates (hoofed mammals) and preserve species further down the food chain.

To critics who accuse re-wilders of playing God, Donlan admits, "there's a clear potential for unforeseen consequences".

He says disease is a worry but, in a process expected to last a century, he isn't too concerned about hybridisation or invasive species.

"It's hard to imagine a runaway population of giant tortoises, let alone a runaway population of lions."

A more detailed proposal will appear this year. Re-wilders want to explore how megafauna shaped eco-systems and promoted species diversity. "We want to restore what we know were important ecological processes in America," says Donlan.

Wolves now roam the French Alps. In Scotland, a businessman wants to stock his estate with wolves, bears, bison and lynx. And in the Pacific there is talk of releasing flightless rails.

"Could rails play a similar ecological role in New Zealand ecosystems to that played by moas 500 years ago?" asks Donlan.

Russian scientist Sergey Zimov has been exploring re-wilding on his 160sq/km Pleistocene Park project at Yakutia in Siberia since 1989. Reindeer, moose, musk oxen and horses are recreating "the ancient mammoth ecosystem". Zimov also wants bison and Siberian tigers.

Changing tundra to steppe may also stall the huge discharge of carbon from melting permafrost that threatens to accelerate global warming.

"It's a shoestring operation," says Terry Chaplin, professor of ecology at the University of Alaska. "There's no major funding. Zimov goes at his own pace. He's currently putting in new fence posts."

Zimov's project raises an issue that divides scientists: were the great Pleistocene extinctions caused by warming weather or by humans? Zimov plumps for the latter, noting that die-offs in America (70 per cent of large animals) and Australia (23 animal species) coincided with the advent of hunters, who used spears and arrows.

This view is shared by Paul Martin, doyen of re-wilders, in Twilight of the Mammoth.

Martin says stealth re-wilding has already begun, as peccaries (New World pigs) spread across the southwest; mustangs elsewhere.

"It's an unplanned resurrection, which nobody is complaining about, and which resurrects fauna that was native here before the extinction 13,000 years ago."

Ultimately, re-wilding offers a back-to-the-future, proactive vision. Traditional conservation, says Donlan, only slows relentless biodiversity loss by "managing extinction". Pristine habitats have vanished.

In a doom-and-gloom world, with nature in retreat and climate change advancing, Pleistocene parks offer hope for endangered species.

Big ideas are needed urgently to counter the planet's sixth mass extinction, the biggest species holocaust since the Pleistocene.

"As a species we're probably largely responsible for this event," says Chaplin. "Do we sit back and try to slow extinction? Or do we try to restore some of the diversity that has been lost?"