Mass timber in construction is often promoted as a climate-friendly alternative to steel and concrete, storing carbon in long-lasting wood products while harvested forests regrow. New research guided by Trent University and in partnership with the Canadian Forest Service sector of Natural Resources Canada is challenging that belief, revealing the climate benefits of timber may not be as straightforward as once thought.
A team of international researchers, including Dr. Andrew Tanentzap, Canada Research Chair in Climate Change and Northern Ecosystems at Trent University and Dr. Erik Emilson, a research scientist at the Canadian Forest Service and an adjunct faculty member at Trent, explored how logging changes the way carbon moves through forest soils and waters. The study, published in the Proceedings of the National Academy of Sciences, found logging makes carbon more reactive and more likely to be released back into the atmosphere, suggesting that global estimates of carbon storage from wood products may be overstated.
"By examining both the amount and type of carbon released after logging, we discovered that forest harvests increased total carbon loss by about 6.4 per cent of what was extracted as timber," explained Professor Tanentzap. "That number may sound modest, but when applied to the millions of hectares logged globally each year, it's a big correction to the calculations on environmental carbon. And this number says nothing about that carbon potentially being more likely to return to the atmosphere than had it stayed in forests."
The three-year experiment in northern Ontario forests near Sault Ste. Marie tracked carbon loss before and after selective logging. Two of the four forests studied were logged midway through the project. The researchers observed a temporary spike in dissolved carbon flowing into downstream waters, as well as lasting changes in the dissolved carbon's molecular make-up. Those changes made the carbon less stable, increasing the likelihood it would return to the atmosphere rather than remain stored in soils or water.
"We are realizing that loss of carbon to water is a really important and missing part of forest carbon accounting models," said Dr. Emilson, who conducts research with students and faculty in Trent's Environmental & Life Sciences graduate program.
The research is the first to measure how both the concentration and composition of carbon washed from soils responds to logging. The findings highlight the need to refine forest management practices to better preserve the climate benefits of wood harvesting.
"Results indicate that some logged forests may shift from being a carbon sink to carbon neutral, and, in some cases, a carbon source," says Dr. Erika Freeman, a former Ph.D. student co-supervised by Prof. Tanentzap and Dr. Emilson and a lead author of the study.
Learn about the Environmental & Life Sciences graduate program at Trent University and discover more research by Canada Research Chairs at Trent.
