LONDON—Elk, roe deer, wild boars, and other wildlife are thriving in a radiation-contaminated preserve largely off limits to people near the Chernobyl nuclear power plant in Ukraine, researchers have found. In a study published today, scientists report “no evidence of a negative influence of radiation on mammal abundance” in the Chernobyl exclusion zone straddling the Belarus-Ukraine border. Much of the 4200-square-kilometer zone was evacuated after the nuclear plant’s unit 4 reactor exploded in 1986, sending a radioactive plume over Europe.

“When humans are removed, nature flourishes, even in the aftermath of the world's worst nuclear accident,” says co-author Jim Smith, an environmental scientist at the University of Portsmouthin the United Kingdom. But some scientists argue that the study glosses over findings showing that the radioactive contamination has damaged individual animals.

The work relies on data collected several years ago in Belarus. Between 2008 and 2010, Belarusian scientists counted animal snow tracks in the Polesie State Radioecological Reserve—the Belarus sector of the exclusion zone. They had also tallied animal numbers by helicopter in the 10 years after the disaster. Analyzing the data, Smith and his colleagues found no correlation between contamination levels and animal track counts, they report today in Current Biology.

In fact, they found that mammal populations in the exclusion zone rose after the accident—apart from a dip in boar numbers between 1993 and 1994—suggesting that hunting, forestry, and agriculture had suppressed wildlife numbers before 1986.

“We're not saying radiation is good for animals, but we're saying human habitation is worse,” Smith told reporters at a press briefing here on Friday. Co-author Tom Hinton, from the Institute of Environmental Radioactivity at Fukushima University in Japan, acknowledges that the study did not probe how the radioactive contamination has affected individuals. “Without doubt,” he says, animals near Chernobyl and the Fukushima power plant in Japan—where three reactors melted down after the March 2011 earthquake and tsunami—suffered genetic damage. “The million-dollar question is: 'What is the significance of this?' We don't really know,” Hinton said at the press briefing.

Ron Chesser, a biologist at Texas Tech University in Lubbock, says the paper concurs with his own work, which found that small mammals were abundant and diverse around Chernobyl in the 1990s. “Their data are much more complete and exhaustive than ours,” he writes in an email. “They are to be commended on a Herculean effort to finally put this debate to rest.”

But some experts insist the debate is not over. Anders Møller, an ecologist at University of Paris-Sud in Orsay, France, says he has found “strong effects” of radiation on animals at Chernobyl, such as a smaller brain size in birds. And working in the Ukraine side of the exclusion zone in 2009, Møller found that the abundance of mammals decreased as radiation levels increased. Møller also questions the reliability of the Belarusian data. “Quite a lot of my colleagues there were put in home confinement for several years because they published negative results,” he says. “I'd have been at ease with these findings if [they] could be independently verified.”

Smith says he is “fully confident” in the integrity of the findings. “I've worked closely with scientists from Belarus for over 20 years and my experience is that they have just as much (if not more) integrity as Western scientists,” he told Science in an email.