Radiation from Russia's 1986 Chernobyl nuclear disaster has had a lasting negative impact on the region's trees, a study suggests.

While the worst effects in surrounding forests were recorded in the "first few years" after the accident, surviving trees were left vulnerable to environmental stress such as drought with young trees particularly affected, researchers said.

Their study is the first to look at the impact of radiation release on a large, landscape scale, they said.

"Our field results were consistent with previous findings that were based on much smaller sample sizes," study co-author Tim Mousseau from the University of South Carolina said.

"They are also consistent with the many reports of genetic impacts to these trees," he told BBC News.

Mousseau has been carrying out field studies since 1999 inside the 19-mile exclusion zone declared around the site of the 1986 disaster.

"Many of the trees show highly abnormal growth forms reflecting the effects of mutations and cell death resulting from radiation exposure," he said.

Mousseau and his fellow researchers say they hope to follow up their Chernobyl study with similar investigation of the Fukushima region in Japan, to measure the impact of the March 2011 nuclear accident there.