NORWAY: September 11, 2008


OSLO - Old forests from Alaska to Russia soak up vast amount of greenhouse gases as they age and are wrongly overlooked as a weapon in a UN-led fight against global warming, a study said on Wednesday.


"New growth continues in forests that are centuries old," an international team of scientists wrote in the journal Nature of old forests outside the tropics that make up 15 percent of the world's total tree-covered area.

Plants soak up heat-trapping carbon from the air as they grow and release it when they die. Until now, most scientists have reckoned that mature forests have a neutral impact on the climate, with any new trees merely replacing others that die.

The report, by scientists in Belgium, the United States, Germany, Switzerland, France and Britain, estimated that old-growth forests outside the tropics absorbed a net 1.3 billion tonnes of carbon a year with ever denser vegetation.

That is almost as much as the total annual industrial greenhouse gas emissions by the 27-nation European Union.

"Until now there was a belief that ecosystems -- like weeds, bacteria in a pond or forests -- reach carbon neutrality when they age," lead author Sebastiaan Luyssaert of the University of Antwerp told Reuters.

"We find no support for that idea," he said. The scientists urged greater protection for temperate forests and northern pine forests such as in Siberia, Canada, the Nordic region or Canada.

The forests studied, from 15 to 800 years old, kept on growing thicker roots and branches while carbon-rich leaves and other debris built up in the soil. And new vegetation quickly replaced fallen trees that could take decades to rot.


REDWOOD LIMIT

Still, forests could not go on absorbing more carbon for ever. Forests along the Pacific coast of the United States, where giant redwoods flourish, seemed at the limit with between 500 and 700 tonnes of carbon per hectare (2.5 acres), they said.

And the scientists said there was too little data to know if tropical forests, less affected by seasonal swings and other factors, also kept accumulating carbon as they aged.

Deforestation, often burning of forests to clear land for farming, accounts for 20 percent of greenhouse gas emissions from human sources, according to UN data. Warming can stoke droughts, heatwaves, more powerful storms and rising seas.

Climate negotiators from 190 nations, meant to agree a new UN pact to fight global warming by the end of 2009, are debating ways to pay developing nations to slow deforestation from Brazil to Indonesia.

The Nature study urged wider protection for other forests and said that: "carbon-accounting rules for forests should give credit for leaving old-growth forest intact."

"The focus on deforestation has been limited to the tropics," Luyssaert said. "We kind of forgot about the forests in places like Siberia, Canada and Alaska. Hopefully we can draw attention to them."

-- For Reuters latest environment blogs click on: http://blogs.reuters.com/environment/ -- (Editing by Matthew Jones)


Story by Alister Doyle, Environment Correspondent


REUTERS NEWS SERVICE