Dartmouth College Professor Andrew Friedland believes that soil disturbance during logging leads to deep carbon being released. He is joined here in the research by students Chelsea Vario (center) and Taylor Hornig. Photo by Eli Burakian/Dartmouth College.
Most New Englanders would agree that one way to reduce our environmental impact is to reduce our use of fossil fuels. And most would also agree that switching to wood is a step in the right direction, especially since it is a local resource that provides local jobs. But Dartmouth College Professor Andrew Friedland warns that, while wood is a better choice than fossil fuels, it may not be as environmentally sound as once thought.
“All energy choices are bad when it comes to the environment,” he said, “and even wood has some problems.”
According to Friedland, the calculations used to quantify the carbon dioxide released when trees are burned for fuel neglect to account for the carbon released from deep in the soil as a result of the logging process. It has long been believed that carbon in the mineral soil two feet or more beneath the surface remains stored there after logging, but Friedland’s recent research says that may not be true.
“It seems like the disturbance at the surface changes conditions deeper in the mineral soil, causing carbon that had been content to sit there to end up in the atmosphere,” he said. “So when we say we’re going to use wood, there may be additional carbon dioxide resulting from our use of wood that we’re currently not accounting for.”
In a research paper published in the journal Global Change Biology: BioEnergy, Friedland studied sites at the U.S. Forest Service’s Bartlett Experimental Forest in New Hampshire that had been logged at various times over the last 75 years. By comparing the physical and chemical properties of the soil at these sites to uncut sites, he found evidence of reduced carbon in the deep mineral soils where logging had occurred. Friedland concluded that this is because carbon was released due to logging.
“We’re not exactly sure how it works,” he admits, “but something is taking place at the surface – maybe decomposition of organic matter – that is allowing the downward transport of greater quantities of nutrients or microorganisms that is stimulating bacterial growth and microbial activity down below, which releases the stored carbon.”
While it’s easy to imagine how industrial-scale logging might disturb the deep mineral soils, Friedland says that his results came from sites that used “relatively gentle logging practices on level terrain with all attempts being made to take care and log responsibly.”
Based on his calculations of carbon released from mineral soils, Friedland says that logging and burning wood for fuel releases 5 to 10 percent more carbon dioxide than previously estimated. And he believes the slow release of carbon after logging probably continues for about 50 years.
“It’s a phenomenon that could last for a while, so when we’re doing things to try to improve the situation with carbon dioxide in the atmosphere in the future, we have to be cognizant of the unintended consequences of our actions,” he said. “Biomass is not a zero-emission fuel source.” But it’s still far better than fossil fuels.