If you cut down a forest to save a mountain, does it count as eco-friendly? That's the crux of the debate going on before the N.C. Utilities Commission that could shape the state's definition of renewable energy.

In the 2007 renewable energy measure, Senate Bill 3, the state mandates that 12.5 percent of the energy sold in 2012 come from renewable sources. Duke Energy is trying to meet that requirement by burning both wood scraps and whole trees cut into chips to generate power at two of the company's oldest coal-burning plants, Buck Steam in Rowan County and Lee Steam in South Carolina.

"Woody biomass plays an extremely important role in our plans to bring cost-effective renewable energy to our customers," says Duke Energy Carolinas spokesman Jason Walls. "We believe by establishing a market for wood to generate electricity, we can provide that proper level of incentives for people to replant and to continue to grow trees."

But some environmental groups are balking at the proposal. They argue that without standards to distinguish between certified sustainable forests and those that are merely clear-cut, it's uncertain that the trees will be replaced. Critics noting that SB 3 says nothing about using whole trees. It's also unclear if woody biomass is carbon-neutral.

Will McDow, a biomass energy specialist for the Environmental Defense Fund, says North Carolina needs a broader statewide biomass policy to ensure that materials aren't overused.

"There are a lot of questions about how much more wood can we demand from those lands before we undermine the social and economic benefits," McDow says. "There's a much bigger state policy that needs to be put into place before we think about opening up this definition."

The Southern Environmental Law Center is joining EDF to oppose Duke Energy's biomass plan. SELC Senior Attorney Gudrun Thompson agrees that large-scale biomass needs to be regulated and that the N.C. Department of Environment and Natural Resources can write and enforce rules governing sustainable harvesting.

"One thing that hasn't really been brought out in this case is the fact that when you talk about renewable energy resources, the fact that something is considered renewable doesn't necessarily mean that it's clean, and using it to the max is going to have environmental benefits," she says.

A report by the state Division of Air Quality shows that burning new wood sources can emit more carbon monoxide, nitrogen oxide, particulate matter and carbon dioxide than new coal.

And Massachusetts is reconsidering wood-burning power plants after a study found this type of biomass releases more greenhouse gases than coal, according to a June article in USA Today.

Nonetheless, the North Carolina Forestry Association supports wood energy.

"Why wouldn't we?" says the association's executive vice president, Bob Slocum. "It's simply another market for wood, and in our view one of the reasons we've got as much forest land and as much timber as we do is because it has economic value. Creating an additional market for wood encourages landowners to buy more."

MeadWestvaco Corp., a packaging supplier and office supplies manufacturer based in Richmond, Va., contends that whole trees fall outside of Senate Bill 3's renewable energy definition, and the company opposes Duke Energy's plan.

Dennis Hazel, a professor of forestry at N.C. State, isn't surprised by the company's stance. If Duke Energy is allowed to use large-scale woody biomass, it would drive up the price of wood fiber, MeadWestvaco's highest operating cost.

"If I worked for MeadWestvaco, I wouldn't want wood energy either," he admits. "I would have to pay more for my paper material."

Mills in North Carolina enjoy the lowest pulpwood prices in the nation, Hazel says, and woody biomass would create competition for wood thinnings, which are piling up too quickly as paper mills experience a decline in business.

Hazel, an extension specialist, says he's unsure about lawmakers' intentions when they crafted SB 3, but he supports burning whole trees for energy.

Woody biomass makes sense, he says, because about a third of the state's tree stands are overstocked and could be unhealthy if not harvested.

In the Southeast, loggers cut trees with large machines. The entire tree is dropped to the ground, minus a few limbs and branches that break off. The tops are removed and the trunks are delimbed. Machines often damage other trees as trunks and limbs are dragged in and out of the forest. What remains, Hazel says, is a forest floor littered with goodssticks, branches and chips, referred to as "logging residue"that currently lack a market. Hazel says the whole trees should count as residue, too.

"Whole trees are a part of normal logging debris. Those need to come out because they aren't going to make merchantable trees, and what ends up happening is if the next stand of trees is going to be planted, they need to bring in heavy equipment and move them out of the way," Hazel says, adding that the remaining trees are typically crooked and unwanted.

But McDow cautions that the new market could create unintended consequences if not properly managed.

"If those treetops all of a sudden have value to a landowner and get sold to an energy facility, then at the next rainfall, what happens to that soil?" he asks.

"Does it flow into the rivers? These are the kinds of questions that the state hasn't grappled with yet."

Bob Bennink, the utility commission's general counsel, expects a ruling to take at least another month. Commission staff is still filing the second volume of testimony from the July 14 hearing. Once that's complete, each party has 30 days to file briefs before the commission reconvenes and prepares a written decision.

UNC announced plans to replace coal with renewable energy by 2020, but it included language that says woody biomass, if used, must come from "certified 'sustainably managed' forests," as determined by third-party verification.

Third-party certifiers include the Forest Stewardship Council, which requires a fee from landowners to earn certification, the Sustainable Forestry Initiative, which only applies to industry-owned land, and the American Tree Farm System, which is free, but some groups don't recognize this certification.

While UNC policy includes language intended to prevent the university from supporting forestry practices that threaten the environment, Hazel questions if the campus can meet that standard.

"It's a fairly small percentage of our total land in North Carolina that's under one of those three programs," says Hazel, who gave a biomass presentation to the UNC Energy Task Force. "I have some concern if they can meet a fairly large need."

Hazel says a state regulatory agency could resolve the problem, or the state could adopt harvesting guidelines, following Minnesota's lead.

If Duke Energy is successful in its application for Buck and Lee, it could provide a new avenue for woody biomass to be sourced. If not, the energy generators will need to reassess other renewable sources.