Nearly 30 years after the Chernobyl nuclear disaster in Ukraine, elk, deer, boar and wolves abound in the exclusion zone deserted by humans, researchers say in an international study.

The study, published Monday in the Current Biology journal, shows that there at least as many of these mammals inside the 1,600-square-mile (4,200-square-kilometer) perimeter around the nuclear plant that exploded in April 1986 than in uncontaminated nature reserves.

Researchers counted the animals by aerial observations of the large zone devastated by a fire and an explosion of one of the plant's nuclear reactors.

They found that there are seven times more wolves in the exclusion zone than in nearby parks.

"It's very likely that wildlife numbers at Chernobyl are much higher than they were before the accident," said Jim Smith of the University of Portsmouth in Britain.

"This doesn't mean radiation is good for wildlife, just that the effects of human habitation, including hunting, farming and forestry, are a lot worse."

Early studies after the nuclear disaster revealed major radiation effects on the exclusion zone, including a sharp decrease in the animal population.

The latest observations show nature's resilience and could provide insight on the long-term impact of the more recent 2011 Fukushima nuclear disaster in Japan.

The helicopter survey data found growing abundance of elk, roe deer and wild boar from 1 to 10 years after the accident.

A short-term reduction in the wild boar population was linked to a disease outbreak not related to radiation exposure.

These increases coincided with a drop in elk and wild boar populations in other parts of the former Soviet Union.

"These unique data showing a wide range of animals thriving within miles of a major nuclear accident illustrate the resilience of wildlife populations when freed from the pressures of human habitation," said study co-author Jim Beasley at the University of Georgia.