Some of the most distinguished scientists in the US have written to UK energy secretary Ed Davey, urging him to abandon the government's "misguided" subsidies for companies burning wood pellets to generate electricity, such as the Drax plant in Yorkshire.
The biologist, Dr E.O. Wilson and Professor Daniel Kammen, an energy adviser to the US State Department, are among 60 signatories to a letter seen by the FT. It warns that UK energy policies are stimulating an "explosive growth" in wood pellet mills that will not reduce carbon emissions and which threatens important native forests.
This is a fresh complication for Drax, which is likely to receive around £200m of subsidies this year for converting part of its coal power plant to burn wood pellets imported from the US instead.
The so-called biomass subsidies will help the UK meet EU targets requiring the bloc to get 20 per cent of its energy from renewable sources by 2020.
One of the biggest coal power plants in Europe, Drax will need at least 7m tonnes of wood pellets a year once it has converted three of its six boilers to wood. It is still considering plans to convert a fourth, meaning its annual pellet demand could exceed 9m tonnes and its annual subsidies could reach £940m, according to London energy analyst Roland Vetter.
"Demand for wood pellets in the UK and Europe is fuelled by misguided energy policies, which incorrectly assume that burning wood will lower carbon emissions and help address climate change," says the letter to Mr Davey, written by Dr William Schlesinger of New York's Cary Institute of Ecosystem Studies.
"These policies appear to subscribe to the wood pellet and power industry claim that burning wood is a carbon neutral process because new trees will eventually absorb and store the carbon that was released when wood is burnt."
Drax does not claim its wood-to-power conversion is entirely carbon neutral, but argues overall emissions are lower because its fuel comes from sustainably managed forests, where new trees absorb carbon faster than older ones.
I think the EU conceived these policies in good faith, but they didn't think about what would happen outside the borders of the EU
The company says its pellets mainly come from wood waste such as sawdust, offcuts or forest thinnings, rather than large healthy trees that absorb the carbon dioxide emissions which are warming the atmosphere to potentially risky levels.
"We are naturally at the low value end of the spectrum and that means it's typically residues," said Drax spokeswoman Melanie Wedgbury.
Wood pellet exports from southern US states where Drax is getting most of its fuel have more than tripled in the last three years, according to Wood Resources International, a Seattle-based research consultancy.
"The expansion, which is entirely driven by demand for biomass in Europe, has increased pellet exports from 800,000 tons in 2011 to 2.9m tons in 2013," WRI said in a statement. The UK is the biggest importer.
But the scientists behind the letter to Mr Davey say forests are being threatened as a result of what they say are flawed assumptions about the environmental benefits of burning wood instead of fossil fuels such as coal.
"I think the EU conceived these policies in good faith," Dr Schlesinger told the FT. "But they didn't think about what would happen outside the borders of the EU".
Drax is building two of its own pellet plants, in Louisiana and Mississippi, to assure the environmental integrity of its supplies.
Using offtakes from forests such as thinnings can make other trees grow more, which is beneficial, said one of the letter's signatories, Daniel Kammen, professor of energy at the University of California, Berkeley.
"The problem, though, is the economic drivers," he said, explaining demand for wood pellets can lead to greater harvesting of standing forests. "The science and the business are in conflict here."
The scientists' letter to Mr Davey says nearly 90 per cent of southeastern US forests are privately owned and there are few regulatory safeguards to ensure harvested trees are replaced by sustainably managed new forests.
In addition, mounting European demand for pellets means some exporters are now eyeing wood from important native forests, it says, and there is growing evidence that trees are the main source of the wood pellets exported to the UK from the southern US, rather than wood waste.
European environmental groups are also anxious to see a change in the UK's policies. "The scientific evidence on this is stacking up and scientists are frustrated no one is listening to them," said Kenneth Richter of Friends of the Earth in London.
The energy department said the UK government was committed to using bioenergy wisely and had recently strengthened standards.
"We are also gathering evidence for our next bioenergy strategy and will review and tighten greenhouse gas standards that will apply to new biomass generation from April 2019," a spokeswoman said.