WASHINGTON: Global warming is helping trees to grow at a faster rate now than they have done in the past 200 years due to higher temperatures and more carbon dioxide into the atmosphere, American researchers have claimed.

After studying the growth of 55 forests in the eastern United States for over 20 years, the scientists from the Smithsonian Environmental Research Center in Maryland found that the recent tree growth "greatly exceeded the expected growth".

They suggested that global warming is helping trees to grow faster as it brings higher temperatures, longer growing seasons and more carbon dioxide into the atmosphere.

In one forest, studied by the researchers, an extra 1.8 tonnes of timber per acre is appearing each year. "The trees, in Maryland, are sprouting up more quickly than at any time in the past 225 years," the scientists said.

Lead researcher Geoffrey Parker said: "We made a list of reasons why these forests could be growing faster and then ruled half of them out".

"The best explanation was a response to climate change, he was quotes as saying by the journal Proceedings of the National Academy of Sciences.

In the past 22 years, carbon dioxide levels where the study was conducted had risen 12 per cent, the average temperature had increased by nearly three tenths of a degree, and the growing season had lengthened by 7.8 days.