Carbon Release an Issue in Woody Biomass Use for Energy Production

February 9, 2012 10:17 AM

The following story was written by a University of Missouri student as part of the 2011 Sonja Hillgren/Farm Journal Ag Journalism Field Reporting Institute. Learn more.

By Emily Garnett
Deep inside Pioneer Forest, which sprawls across 154,000 acres in central and southeastern Missouri, the roar of a chainsaw could be heard.
The roar stopped abruptly and in the brief silence that followed, Jay Duncan, co-owner of J&G Logging, hoisted his orange Stihl chainsaw and made a hasty dash away from the tree. With a prolonged cracking sound and an enormous crash, the branches, limbs and sizeable trunk of a mature scarlet oak hit the ground.
What Duncan heard was the death of a tree. What he couldn’t hear was the beginning of the slow, silent release of carbon into the atmosphere as the tree began its decaying process. If the dead scarlet oak is used as "woody biomass," a wood product burned for energy production, the carbon release will be even swifter.
Thanks to a study known as the "Manomet Report," the sound of trees releasing carbon into the atmosphere now rings loudly in the ears of many scientists and foresters. Even though the study’s conclusions could limit the size and impact of an imminent woody biomass industry, many foresters and environmentalists fear for the health and survival of Missourian forests.
The U.S. Department of Agriculture has long promoted using trees to produce energy, in the place of fossil fuels such as coal and natural gas. Fossil fuel supplies are replenished over millennia, but trees can be regrown within 30 years.
Because of this fast growth, the logic went, trees can rapidly reabsorb the carbon they release into the atmosphere when they’re burned, thus making wood a carbon-neutral source of energy.
"Up until very recently in the United States, woody biomass has gotten a free pass," said Peter Becker, a forest ecologist and research coordinator with the Eastern Ozarks Forestry Council.
But in June 2010, the Manomet Center for Conservation Sciences, a non-profit environmental research organization based in Massachusetts, released a study that refuted the long-standing belief that burning wood for energy is a carbon-neutral event.
"Forest biomass generally emits more greenhouse gases than fossil fuels per unit of energy produced," creating an initial "carbon debt" when wood products are first burned, the report concluded.
Tree regrowth will eventually remove this carbon from the atmosphere, but it can take up to 40 years before the full debt is repaid. So, only decades after the initial burning does biomass "begin yielding carbon dividends in the form of atmospheric greenhouse gas levels that are lower than would have occurred from the use of fossil fuels," the study concluded.
"When I read the report my mouth dropped open, literally," Becker said. "It has serious, serious implications."
In part due to the issues raised in the Manomet Report, the U.S. Environmental Protection Agency has revised a report proposal that will examine how a variety of energy sources, including wood, release greenhouse gases into the atmosphere.

The changes could limit how much wood is accessible for biomass facilities such as wood-generated power plants, said Kenneth Skog, a forest economist with the U.S. Forest Products Laboratory in Madison, Wis.
The EPA proposal suggests assigning points to various methods of harvesting wood, which would measure each method’s potential to reduce carbon in the atmosphere.
The points, called "biogenic accounting factors," would range from 0 to 1. A score of 1 would mean none of the carbon released by that method is immediately absorbed by new growth and a score of 0 would mean all of the carbon released is quickly absorbed by new growth.
Certain methods, such as logging whole trees specifically for wood fuel, will most likely score higher, since the Manomet Report has shown that the carbon emissions from this method will stay in the atmosphere for decades before new growth can catch up and re-absorb them.
But other methods, such as using the tree branches and tree tops from logging efforts that are already underway or using mill by-products already available, will have a lower score. These methods do not take any additional trees off the land, and the resulting by-products need a market, Skog said.
More than anything else then, Becker maintains, the conclusions of the Manomet Report have reinforced the need for careful forestry management in Missouri.

 The Report itself noted that the environmental impact of the woody biomass industry will ultimately "depend on future forest management actions."

This is a sensitive issue in the state of Missouri, which has no logging regulations.  

"Loggers with a chainsaw are the ones managing timber in Missouri," said Scott Brundage, a certified Missouri forester and tree farmer.
The "chip mill fiasco" of the 1990s demonstrated the threat new markets for wood pose to Missouri woodlands, Brundage said. Two high-capacity chip mills moved into the state in 1997, and many woodlot owners allowed loggers to clear cut their properties for a quick profit.

But a different problem faces Missouri forests today. The state’s woodlands produce nearly three times as much wood as loggers cut, and forests are becoming overcrowded with undesirable and invasive tree species, Brundage said.
"Missouri leads the nation in "cull" trees — worthless trees," he said.
In light of this, Brundage believes the biomass industry could benefit Missouri forests.
"Biomass fuel could be the greatest management tool to come along," he said, "Now we have a market for low-quality, low-value wood."
But Brundage worries that without logging regulations, the new market for wood could devastate forests across the state.
Skog also promotes restrained logging practices—from a carbon emissions standpoint. The practice of clear cutting releases large amounts of carbon dioxide into the atmosphere. Without any standing trees to start re-accumulating the carbon, several decades must pass before tree saplings can grow large enough to repay the initial debt, much less remove additional carbon from the atmosphere, Skog said.
Thus, the preferred management plan involves a gradual, selective removal of trees from forests, practices enforced by Pioneer Forest, where Jay Duncan spends his days logging.
Here, foresters Jason Green and Brandon Kuhn evaluate individual stands of trees, an acre or two at a time, marking the unhealthy or undesirable species and mature trees ready for logging, keeping in mind spacing and the natural life cycles of the forest.
Once J&G Logging cuts the selected trees in a stand, no logger will touch that area again for 20 years. This minimally invasive technique of logging, called "single-tree selection," is praised by many foresters and scientists, including Rose Marie Muzika, chair of the MU Forestry Department.
"As ecologists, we often try to imagine how the natural processes take place," she said. "This kind of single-tree mortality, which this harvest method imitates, is a very common natural process in all forests."
The Pioneer foresters are unsure how compatible a woody biomass industry is with forestry practices such as single-tree selection. Green and Terry Cunningham, Pioneer’s forest manager, have voiced concerns about the volume of wood such an industry would require, the lack of logging regulations, and the presence of markets that already use most of the wood industry’s by-products available in Missouri.

But Becker thinks woody biomass and sustainable forest management go hand in hand, especially in light of the Manomet Report. He argues that the wood used in the biomass industry should come from the thinnings and debris left over from selective forest clearings such as those Pioneer foresters oversee.

"We’ve just turned things on their head by saying, do forest management first and cut the trees necessary and the byproduct could be biomass for energy," he said.
Only using the leftover wood from selective forest clearings may limit the size and scope of the biomass industry, Becker conceded.
"Biomass is do-able," he maintains, "just not on the scale industry is fantasizing about."

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