Less than a mile from what is left of Chernobyl's ill-fated fourth reactor, a pair of elks is grazing nonchalantly on land irradiated by the world's worst nuclear accident. In nearby Pripyat, an eerie husk of a town where 50,000 people used to live before they were forced to flee on a terrifying afternoon in 1986, a Soviet urban landscape is rapidly giving way to wild European woodland.
Radiation levels remain far too high for human habitation but the abandoned town is filled with birdsong and the gurgling of streams forged by melting snow. Nobody thought it possible at the time but 20 years after the reactor exploded on 26 April 1986, during an ill-conceived "routine" Soviet experiment, Chernobyl's radiation-soaked "dead zone" is not looking so dead after all.
The zone - an area with a radius of 18 miles in modern-day Ukraine - lives on in the popular imagination as a post-apocalyptic wasteland irreparably poisoned with strontium and caesium that would make a perfect setting for the next Mad Max movie. It is a corner of Europe associated with death and alarming yet nebulous stories of genetic mutation, a post-nuclear badland that shows what happens when mankind gets atomic energy wrong.
The reality, at least on the surface, is starkly different from the mythology, however. The almost complete absence of human activity in large swaths of the zone during the past two decades has given the area's flora and fauna a chance to first recover and then - against all the odds - to flourish. It is a paradox that has disturbed opponents of nuclear power who point to the appalling, still unknown, human cost of the tragedy and the terrifying invisible pollution that looks likely to blight the area for centuries.
That something remotely good could come of something so obviously awful does not fit with orthodox thinking about nuclear power and its all too apparent risks. The picture is further complicated by the fact that the true human cost of the tragedy and the damage wreaked on people's health by the radioactive cloud emitted after the explosion may never be fully known.
Estimates of human fatalities, both direct and indirect, vary wildly, from 41 in the immediate aftermath to tens of thousands in the years that followed. It is estimated that five million people were exposed to radiation in Ukraine, Belarus and Russia and that the radiation fallout - equivalent to 400 Hiroshimas - triggered an epidemic of thyroid cancer that has yet to abate.
Doctors claim convincingly that cancer rates are far higher than they were before 1986 and that thousands of Ukrainians and people in neighbouring Belarus (worse affected than Ukraine because of the wind direction at the time) may have died prematurely as a result.
In the dead zone's so-called Red Forest, a pine forest that took the brunt of the radioactive explosion, radiation levels today can be as high as one roentgen, more than 50,000 times normal background levels.
Elsewhere, however, levels are much lower - to the point where large animals such as elks, wild horses and wild boars appear to be enjoying normal life spans. It is an unlikely scenario that has begotten another improbable development - the arrival of a trickle of intrepid eco-tourists who come to marvel at an area that some, controversially, claim is one of Europe's most promising wildlife havens.
Astonishingly, most of the animals, with the exception of the herds of wild Przewalski's horses brought in to gnaw on radioactive grass to guard against forest fires, appear to have returned to the zone of their own accord. The most recent count by the authorities showed that the zone (including a larger contaminated area in neighbouring Belarus) is home to 66 different species of mammals, including 7,000 wild boar, 600 wolves, 3,000 deer, 1,500 beavers, 1,200 foxes, 15 lynx and several thousand elks.
The area was also estimated to be home to 280 species of birds, many of them rare and endangered. Breeding birds include the rare green crane, black stork, white-tailed sea eagle and fish hawk. Wild dogs are also in evidence, though they are prime targets for wolves, a detail that prompted the American thriller writer Martin Cruz Smith to call his latest novel, which is partly set in the zone, Wolves Eat Dogs.
The only animal that appears not to have made a comeback is the bear. But ecologists say the return of large predators such as wolves is a sure sign that things are moving in the right direction.
Sergey Franchuk, a guide and local expert who has been associated with the area since 1982, says he believes the radiation has purified the soil in an inexplicable way. "We think that the land has been cleansed," he says, pointing up a long, straight road flanked with pine forests that later give way to silver birch forests straight from the pages of Boris Pasternak's Dr Zhivago.
"Nature is flourishing here, even more so than it was before the accident. When Viktor Yushchenko [the Ukrainian President] came here last year, he even suggested turning the area into a nature reserve. That gives you an idea of what is happening here." What Sergey doesn't mention is that Mr Yushchenko simultaneously floated the idea of turning the exclusion zone into a dump for foreign nuclear waste.
Anywhere else, such a plan would have ecologists up in arms but here some nature-lovers - who seem to regard radiation much in the same way as keen gardeners in the West regard manure - think it is nothing to fret about. "(If it happened) it would not take up a huge amount of territory," says Mary Mycio, author of Wormwood Forest, a book that describes itself as a natural history of Chernobyl.
Ms Mycio, an American foreign correspondent in the area, and a biologist, was one of the first people to begin cataloguing nature's unlikely comeback in Chernobyl and has made 24 different trips to the dead zone.
"On the surface," she says, "radiation is very good for wildlife because it forces people to leave the contaminated area. They removed 135,000 people from an area twice the size of Luxembourg. The people there now carry out very localised activities and in vast regions of the zone there are no people. It is a radioactive wilderness and it is thriving."
Hunting and fishing in the dead zone is prohibited for obvious reasons and according to Mr Franchuk there are only 337 squatters - people who obstinately refused to be resettled - living in the zone. The vast majority of these settlers are elderly and though many of them talk about radiation as if it were about as harmful as rain, none of them lives in the heart of the dead zone, a six-mile exclusion area that even they dare not inhabit.
A small army of about 6,500 nuclear workers comes in and out of the zone on temporary assignments to try to patch up the cracked sarcophagus that covers the stricken reactor, but none of them is a permanent resident. Their impact on the environment is so minimal that even the cooling ponds of the power station are said to teem with fish.
Ms Mycio argues that something good has come out of something bad. "The sight of wild horses here is moving. I saw a wolf in broad daylight once, and the bird-watching is excellent." She admits, however, that some scientists question what is happening to flora and fauna at a cellular and genetic level.
The few studies that have been done have exposed minor genetic changes in small animals and birds such as mice and barn swallows, including depressed fertility. But Ms Mycio argues that animals are adapting to living with radiation and are even building up a resistance to it. She insists there is no serious evidence of animals mutating in the zone.
"Nature's law is the survival of the fittest. In the wild, mutants die. And if they do survive, they are like the partly albino swallows that appeared in the early years after the disaster. They were not considered attractive and found it hard to mate, so their mutations didn't pass on to future generations."
Sergey Franchuk, a self-confessed optimist, is among the many who believe that animals sense whether the land they live on is poisoned or not. He sees their return to Chernobyl as evidence that the eco-system is rapidly cleansing itself, a state of affairs he believes could see people moving back to parts of the zone within 15 years.
Others think that it will be centuries and warn that if humans do return to the zone in significant numbers, the area's unique flora and fauna will be put at risk.
In the aftermath of the accident, many trees and plants were killed outright by radiation and it seemed as if nothing would grow again in their place. But the abandoned settlements of Chernobyl appear to have become the site of an unlikely renaissance.
The town of Pripyat, just two miles from reactor number four, is a case in point. Before the accident it was a model Soviet town populated by power-station workers, its shiny concrete tower blocks, crowned by giant steel Soviet emblems, symbolic of a bright atomic future. Its creches, shops, and apartments were regarded as the best the USSR could offer. Now its central Lenin Square is a shadow of its former self.
Trees encroach on its public spaces, steps are carpeted in grass and moss. As the winter snow melts, the paving stones become a shallow river bed, as water runs into a drainage system that has long since ceased to be serviced. And as the concrete cracks, nature advances. In one of the eerie children's play areas, the only sound is cheerful birdsong. Branches spread across what used to be an enclosure for bumper cars, a giant Ferris wheel stands idle, and trees and weeds press in on every side. In another 20 years it may be hard to discern the town's features at all.
In the village of Illintsi, Maria Shaparenko, 82, one of the stubborn resettlers, claims Chernobyl was always a beautiful area and that nothing has really changed. "It's very nice here in summer, everything blooms. In fact nothing is wrong here, it's just that people have been scared off by the radiation." Outside in her yard a cockerel crows, and for a minute, it seems like Chernobyl really is like anywhere else.
But a few doors away, Roman Yushchenko, an old man riddled with cancer, is turning black beside a chamber pot of his own blood-red urine.
Chernobyl may have turned into a sanctuary for flora and fauna. For human beings it remains less welcoming.
Scientists divided over radiation and regeneration
When top predators such as wolves and eagles return to a damaged habitat, it is a sure sign that the ecosystem is once again healthy and vibrant. For several years, ecologists have reported many sightings of rare species within the Chernobyl exclusion zone which are hardly ever seen in other parts of Europe.
Robert Baker, a biologist at Texas Tech University who has made more than a dozen scientific excursions into the zone, said the diversity of wildlife around the stricken plant was what might be expected in a nature park dedicated to conservation.
"The benefit of excluding humans from this highly contaminated ecosystem appears to outweigh significantly any negative cost associated with Chernobyl radiation," Dr Baker said.
In a comprehensive assessment of the damage caused by the Chernobyl accident, the British ecologists Jim Smith and Nick Beresford point out that radiation levels considered potentially dangerous to humans have little if any effect on wildlife.
"Nearly 20 years after the accident there is some (often contradictory) evidence of continuing radiation damage to organisms, but this appears to be relatively minor (although poorly understood)," they say in their book, Chernobyl - Catastrophe and Consequences.
"Radiation is considered to be a risk to humans when there is a small, but significant, probability of cancer induction in later life. Though cancer induction in animals is possible, a small additional cancer risk does not affect wild populations as a whole. Animals in the wild are less prone to cancer than human populations. They are most likely to be killed by natural predators or starvation before they reach an age at which cancer risk increases," they say.
Not all scientists accept this assessment. Anders Moller and Timothy Mousseau studied swallows in the exclusion zone and found they carry a significantly higher level of "germline" mutations in their sperm and eggs compared to swallows elsewhere.
"Our work indicates that the worst is yet to come in the human population. The consequences for generations down the line could be greater than we've seen so far," said Dr Mousseau, a biology professor at the University of South Carolina.
Steve Connor, Science EditorReuse content