A new report that questions the environmental-friendliness of burning forest wood is sending ripples through Maine, a state that's trying to grow its biomass industry. The report from the Manomet Center for Conservation Sciences claims that burning wood for electricity releases more heat-trapping carbon dioxide than fossil fuels.

"Using wood per unit of electricity emits more C02 into the atmosphere than than coal or oil -- you actually create a carbon debt," says John Hagan, Manomet's president.

He agrees with the industry that biomass is renewable, unlike coal or oil. And that carbon emissions from biomass get cancelled out by the CO2 absorbed by trees before they are turned into wood for burning. But he says it can take a long time for that cycle to happen.

"There's a greenhouse gas debt before there's a dividend. And so the question becomes, how long does it take to pay off the debt before you start to appreciate the the climate benefits of using wood?" Hagan says. "So if it's a large electricity plant, like a 50-megawatt electricity plant, the debt period could be 20 or 30 years before you start to appreciate a carbon benefit."

Hagan says this holds implications for regulators who have timelines to reduce carbon emissions. But a representative of Maine's biomass industry says much of the study, which was commissioned by the state of Massachusetts, doesn't apply to Maine companies, and is giving the entire industry a black eye.

"Harvesting forests is not what the biomass industry does -- it's certainly not what the nine biomass plants do in Maine," says Bob Cleaves, who heads the national Biomass Power Association, based in Maine. He says that virtually all of the biomass in Maine comes from wastewood, such as tree tops and branches left over from logging or landclearing.

While Manomet researchers say that biomass taken from clear-cutting for a development is not an example of sustainable harvesting, Cleaves says it is better than the alternative.

"The land would not have been cleared for the purpose of producing energy," Cleaves says. "And that's an important point because the presence of the biomass industry does not cause land clearing to occur. The presence of the biomass industry, essentially, takes by-products that would have otherwise been landfilled or discarded or decayed."

Hagan of Manomet acknowledges that Maine has a more established forest industry than other states, and that more of the biomass may be coming from logging debris. But he says that Maine would have to account for where all the biomass is coming from to get the full picture of carbon emissions.

Whether biomass is carbon-neutral or not came up during a U.S. Senate vote Thursday on whether to limit the Environmental Protection Agency's power to enforce rules on carbon emissions.

Maine's two Republican senators voted for the measure. Senator Susan Collins said the EPA should not subject biomass, which has been historically treated as "carbon-neutral," to the same permitting rules as those for fossil fuels.

"We have two extreme views being taken within one week, one by our senators and the biomass industry, and the other by this study for Massachusetts officials, and neither gets it exactly right," says Maine Environmental Commissioner David Littel.

"What our view is, together with the Maine Forest Service, is if biomass is sustainably managed and sustainably harvested, it is a essentially carbon-neutral," he says. "If it comes from a development of a retail shopping mall that wood is obviously not going to grow back, the forest won't grow back, therefore carbon dioxide will end up in the atmosphere, essentially permanently."

Littell says that the Manomet report will be an important contribution to the scientific literature for policymakers. The report had more positive things to say about burning biomass for heat. It says heating is a more efficient use of biomass than power generation, and would recover the carbon debt faster, in as little as five years.