The forests of the world sequester carbon in vast quantities: an estimated 289 gigatonnes (Gt) in their biomass alone, according to the Food and Agriculture Organization (FAO) of the United Nations. About half of the dry weight of a tree is stored carbon, which is released when the wood rots or burns. • Substituting wood for other structural materials in construction locks in forest-sequestered carbon while avoiding the environmental scars of mining for metals and concrete constituents, and saving the energy and greenhouse-gas emissions of their manufacture.
Infographics by Tien-Min Liao
New wood technologies, such as cross-laminated timber, nail-lam, and improved glulams, enable buildings to use built-up wood elements from small trees in place of steel, concrete, and even aluminum curtain wall.
But how does increasing the use of wood in building reconcile with reducing the pressure on global forests? Key to understanding the challenge are two distinctions: the distinction between deforestation and wood removal pertains to forest quantity, and the distinction between natural forest and plantation pertains to forest quality.
Deforestation vs. wood removal
Deforestation "implies that forests are cleared and the land converted to another use, such as agriculture or infrastructure," according to the FAO. As forest area declines with deforestation, so does the carbon held in forests—at an estimated 0.5 Gt annually during the period from 2005 to 2010, which puts greenhouse-gas emissions from deforestation at about 15 to 17 percent of global totals, more than the entire transportation sector. Nor is carbon release the only impact of deforestation: biodiversity, hydrocycles, water and soil quality, and human rights and livelihoods all suffer.
Conscientious practitioners in the construction industry may be relieved to hear that wood use in construction is not one of deforestation's key drivers. (Note, however, that sourcing of tropical woods and temperate hardwoods warrants particular care.) Conversion to agriculture, notably palm oil, cattle, soy, and subsistence farming, accounts for about 80 percent of global deforestation, which occurs at its most alarming rates in South America, followed by Africa and many areas of South and Southeast Asia, according to the FAO's 2010 Global Forest Resources Assessment.
In North America, where 90 percent of wood taken from forests is cut for the timber itself—primarily for construction and, decreasingly, pulp and paper—forest area is holding steady. North American forests are now being managed so that they recover from cuts within a relatively short period, either through replanting (reforestation) or natural regeneration.
But there's a hitch. It's not enough that wood removal maintains the quantity of forest. Qualitative factors are critical to forest vitality.
Natural Forest vs. Plantation
A forest plantation, as defined by the FAO, is "a forest established by planting or/and seeding in the process of afforestation or reforestation. It consists of introduced species or, in some cases, indigenous species." Plantations and natural forests occupy a continuum from even-aged monocultures to variously aged mixed species native to a site, but the continuum is a wide one. No one would confuse an old-growth forest and a tree farm. Preventing the unsustainable conversion of natural forests into plantations is one of the primary functions of an effective forest-certification system.
"Certification systems are governing systems where standards, ideas, knowledge, power and debates coincide to produce some type of approach about what constitutes sustainable forest management," says Ben Cashore, director of Yale's Program on Forest Policy and Governance. About 30 percent of the world's forest is designated for production of wood and nonwood products, with a further 22 percent designated for multiple uses, which include wood production. About a fifth of this combined area—some 415 million hectares—is managed according to a certification system.
The forest-certification systems most relevant to the North American building industry include the American Tree Farm System (ATFS); the Sustainable Forest Management (SFM) system of the Canadian Standards Association (CSA); the Forest Stewardship Council (FSC); and the Sustainable Forestry Initiative (SFI). Together these account for more than 99 percent of wood used in U.S. construction, according to a 2008 report of the Yale Program on Forest Policy and Governance.
To date, the United States Green Building Council (USGBC) and the International Living Building Institute (ILBI) have endorsed only the FSC. To ensure that businesses or organizations with a vested interest in extraction cannot capture the policy process, the FSC has a three-chamber format: environmental, social, and economic, each with equal weight. FSC Canada has a fourth chamber, First Nations. The ATFS, CSA, SFI, and many other programs internationally operate under the rubric of the Programme for the Endorsement of Forest Certification (PEFC), initiated by industry and forest-owner associations.