The Manomet Center analysis, however, concludes that there is only a small amount of such leftover wood, and that whole trees will have to be taken to fuel Massachusetts wood-burning power plants.

“The study is not representative on how we plan to operate,’’ he said.

Matt Wolfe of Madera Energy Inc., which is proposing a wood-burning power plant in Greenfield, said the study incorrectly assumes whole trees would be cut to fuel the power plants. Rather, he said, most wood for his plant would come from tree tops and branches left over from logging operations or from storm damage, land clearing for new development, or tree-trimming operations.

“This industry, which has been around for 30 years, takes forest byproducts and combusts them in a way that is carbon neutral,’’ said Bob Cleaves, president of the Biomass Power Association, a national industry group based in Maine.

Advocates of wood burning said that they had not had time to read the full study but that burning wood is renewable and has been viewed as such for years.

The study has important implications for policy as President Obama aims to lower US greenhouse gas emissions some 80 percent by 2050 to avoid the most serious consequences of man-made climate change. Wood is projected to be one of the fastest-growing sources of renewable energy in the next decade, but if the benefits take too long to appear, policy makers under urgent deadlines may choose not to embrace it.

What’s more, that increase in greenhouse gases can take a far longer time for forests to absorb than previously thought — a generation or more in many cases. If a wood-burning power plant replaces a coal-fired one, it can take about 20 years before any net benefits are realized. It can take more than 90 years if a wood-burning plant replaces a natural gas plant.

But the Manomet study shows that wood burning releases more heat-trapping carbon dioxide into the atmosphere per unit of energy than oil, coal, or natural gas.

Wood burning has been promoted as a “green’’ energy source because growing forests can absorb the same amount of greenhouse gases that are emitted from burning wood, essentially canceling out the pollutants.

“These findings have broad implications for clean energy and the environment in Massachusetts and beyond,’’ said Ian Bowles, state secretary of energy and environmental affairs.

The six-month study by the Manomet Center for Conservation Sciences in Plymouth comes amid controversy over the proposed construction of two large wood-burning power plants in Western Massachusetts.

Burning wood to generate electricity can be worse for global warming than burning coal, according to a Massachusetts-sponsored study released yesterday. That surprising conclusion immediately prompted state officials to reconsider substantial financial incentives provided to wood-burning plants.

The study indicates wood burning still may make sense in certain cases. For example, heating buildings with wood is more efficient than wood-burning power plants, and it can start helping the environment by reducing greenhouse gas emissions in as little as five years.

Wood-burning’s environmental benefits can vary significantly, depending on the type of wood or piece of tree being burned, what kind of fossil fuel it is replacing, what type of energy it is producing, and how people manage forests, according to Tom Walker, the study team leader. Many, but not all, types of wood burning create a “carbon debt’’ that growing forests gradually repay by reabsorbing gases before a “carbon dividend’’ begins.

Massachusetts has offered financial incentives for wood-burning power plants since 2002, considering them to be part of a portfolio of renewable power along with wind and solar. By 2020, state electricity suppliers will be required to get 15 percent of their energy from such green sources. Without the credits, wood burning is not competitive with more traditional forms of energy.

But when two large wood-burning (also called biomass) plants were proposed a few years later, in Russell and the one in Greenfield, a large and vocal group of residents opposed them, asserting they would be fueled by cutting trees on public and private lands across Massachusetts.

The controversy reached a crescendo last year, and in December, the state Department of Energy Resources suspended incentives for new wood-burning plants until the Manomet study could be completed. Now that it is, Bowles said his agency will publicly review the study this summer, and develop new rules in the fall. The suspension of credits for new plants will continue until then.

The study counters earlier estimates showing there is plenty of wood available for wood-burning power plants in the state, saying there would not be enough sustainably harvested wood to fuel even one large wood-burning plant. Walker said the study tried to look at what was “economically and socially available’’ from the forests, meaning in part what landowners would realistically sell.

Jana S. Chicoine, who has led the fight against the Russell plant, said she was pleased at the findings, calling the study a “policy earthquake. We always made the case this was not a NIMBY issue but a policy failure and now we have the state saying exactly the same thing,’’ she said.

John Hagan, president of the Manomet Center, said the report leaves policy makers with key questions.

“Do you want to wait 10, 20, 30 years just to get to the point [wood burning] is as good as coal? That is a real social question: Do we as a society want to make the climate worse before it gets better?’’

Beth Daley can be reached at bdaley@globe.com.

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