Photo © W.S. Klem
What can wood EPDs tell us
Earlier this year, the American Wood Council (AWC) and Canadian Wood Council (CWC) published updated cradle-to-gate EPDs for six of the major North American wood products (softwood lumber, plywood, oriented strand board [OSB], laminated veneer lumber [LVL], I-joists, and glue-laminated [glulam] timber).
Wood EPDs are underpinned by the biogenic carbon cycle—in product storage, energy for manufacturing, as well as impacts in the forest. A cycle, by its very nature, is not linear and not well suited for LCA. The complexity of the biogenic cycle warrants detailed explanation.
Difference between biogenic and fossil carbon
As trees grow, they clean the air by absorbing CO2 from the atmosphere. Trees release the oxygen and incorporate the carbon into their twigs, stems, roots, leaves or needles, and surrounding soil. As trees mature and then die, they start to decay and slowly release the stored carbon back into the atmosphere.
This is a closed loop cycling through natural processes of growth and decay. It is also a closed loop cycle when forests are harvested for use in products or energy. The biogenic carbon cycle fundamentally differs from the open/one-way flow of fossil carbon to the atmosphere.
Photo © Chad Davies, Marshall Andrews, and SmithGroup
How would an increase in demand for wood products impact forests?
Many builders and architects are concerned with the impact of increased demand for wood products on forests. Through both empirical evidence as well as economic models, the authors have found demand for wood products results in more forest land, not less. Markets provide economic justification for sustainable forests and good forestry practices.
Responsibly managing forests in a way that balances harvesting and replanting can maintain a large pool of sequestered carbon over the long term. It also provides a sustainable source of wood products that continue to store carbon and offset the use of fossil fuels, hereby reducing atmospheric GHGs.
In terms of resource availability, the U.S. Forest Service’s Forest Inventory Analysis program tracks the volume and health of forests. In 2018, U.S. forests and harvested wood products were a net sink on the order of 663 million metric tons CO2e, which offsets about 10 percent of the nation’s GHG emissions.
The amount of forest area has remained constant since about 1900, and U.S. forests have been net sequesters since the 1950. During this same period, harvests have remained stable or in some cases have increased, such as in the southern parts of the country.
Wood supports a sustainable future
While no one material is the best choice for every application, LCA studies have consistently shown wood has a favorable environmental profile compared with functionally equivalent products. As with any building project, different materials have their own unique trade-offs and benefits based on a project’s design objectives. By understanding the terminology and by using the right tools, the architect’s material assessment—and resulting client communications—can tell a compelling story of a building’s reduced carbon footprint.
Edie Sonne Hall is founder of Three Trees Consulting, where she provides technical expertise to projects involving forest carbon accounting, ecosystem services, green building, life-cycle assessment (LCA), and sustainable forest certification. She serves as facilitator of the North American Wood Products LCA Coordination group, which is made up of wood product LCA experts, representing academia, government agencies, industry associations, and consultants in the U.S. and Canada.
