The American Hardwood Advantage: Carbon-neutral Materials for Today's Zero Tolerance Goals

American hardwoods help offset global warming and benefit the built environment by reducing carbon dioxide emissions.
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Sponsored by The Hardwood Council

It is worth making a distinction between the two major forms of carbon dioxide. Anthropogenic carbon dioxide is derived from fossil fuels use. Conversely, biogenic carbon dioxide is carbon dioxide generated from biomass. Unlike fossil fuel, this latter form of carbon dioxide is considered impact neutral. In other words, carbon dioxide gas emitted in wood combustion and processing is off-set by the carbon dioxide gas taken up by trees as they grow. Through the process of photosynthesis, carbon dioxide and water are taken from the atmosphere and soil for woody tissue production. During the process, oxygen is released back to the atmosphere. Further, woody biomass used for internal fuel requirements during the manufacturing process can be considered advantageous.

Selective Harvesting and Natural Regeneration
Many people are surprised to learn that the U.S. hardwood industry actually "plants" very few trees, but rather relies on the natural regeneration of its native forests. The mature (and hence, larger) trees are harvested as they give off less oxygen and take in less carbon dioxide. By removing the older trees, more sunlight hits the forest floor, which stimulates growth of the younger trees that absorb carbon dioxide at a much higher rate than mature trees. The competition among the young trees creates a vibrant and diverse eco-system capable of sustaining plant and animal life far in excess of anything possible in a mono-culture environment, such as a plantation. In addition, the natural forests of North America thrive without any need for artificial pesticides, fertilizer or even irrigation systems, making American Hardwoods one of the world's truly "organic," as well as sustainable, materials.

There are some issues in determining the carbon neutrality of hardwood, however. Trees in some areas don't absorb as much carbon as trees in others. For instance, the trees in New York City's Central Park absorb more carbon than, say, trees in a carbon-offset forest. Further, carbon sequestration rates vary by tree species, age, soil type, regional climate, topography and management practice. In the United States, fairly well-established values for carbon sequestration rates are available for most tree species. Soil carbon sequestration rates vary by soil type and cropping practice, and are less well documented, but information and research in this area is growing rapidly.

Despite the variations in carbon absorption rates, wood as a material has clear advantages over non-renewable or chemically intensive alternatives. To recap, wood is a renewable resource with the added benefit of storing carbon in its service life. During the process of tree growth, trees sequester carbon and release oxygen, a unique process that relegates biomass-derived carbon dioxide to a carbon-neutral substance. At the end of its service, depending on application, hardwood may be re-used or burned for fuel.

That said, extolling the carbon neutrality of wood only makes sense when the wood has been grown and harvested according to sustainable forestry practices. As hardwoods are selectively harvested, the bio-diversity and integrity of the forest are preserved, and the forest is kept in the best condition to continue to remove greenhouse gases. Sustainable forestry practices ensure that the carbon-absorbing properties of the forest are preserved.

Sustainability of American Hardwoods

Global climate change and tropical deforestation have accelerated public concerns regarding the environmental footprints associated with using wood. In the general public, and even among the design and building communities, there is some confusion about the role wood products play in minimizing impacts on the environment, with some equating cutting trees with inevitable and permanent forest destruction.
However, in a 2008 report, the United States Department of Agriculture Forest Service verified that the average annual net growth for hardwoods is greater than average annual removals. In fact, the average growth to removal ratio is 1.66, which means that for every cubic foot of hardwood removed from the standing inventory, 1.66 cubic feet is added. Statistics show that the number of trees in existence today far exceeds those in the 1950s, with the Forest Service stating that there were 98 percent more trees in 2002 than 1953. While it may take 40 to 50 years for new trees to mature, wood from those trees won't be needed for another 50 to 100 years.

American hardwoods are most prevalent in the eastern half of the United States. In this section of the country, hardwood forests cover about 279 million acres, the equivalent of hardwood trees covering every square inch of New York, Pennsylvania, Ohio, Illinois, Indiana, West Virginia, Virginia, North Carolina, South Carolina and Georgia. This resource, which needs only sunlight, soil and rain water to flourish, is neither scarce nor finite.

Hardwood Research: Carbon Neutrality and Environmental Impacts

Over the years, a number of studies have been done on the environmental impacts of hardwoods. In 2007-2008, the National Wood Flooring Association Industry Research Foundation conducted a life cycle analysis of wood flooring in conjunction with the Consortium for Research on Renewable Materials (CORRIM), in Madison, Wisconsin. The study evaluated solid hardwood flooring compared to other flooring alternatives, such as vinyl, linoleum and carpet, with regard to air emissions, energy use, water use, and product service life, finding solid hardwood flooring to be desirable from an environmental impact standpoint, a conclusion that is consistent with previous studies in Europe.

 

That wood flooring has the least environmental impact of all other flooring options studied stems from several factors:

  • Comparatively benign air emissions. Wood flooring was shown to have no emissions for methane, nitrogen oxide and other particulates, and minimal emissions for carbon dioxide.
  • Comparatively less water consumption. Solid hardwood flooring and generic vinyl composition tile use substantially less water than other alternatives, with water use for production of hardwood flooring confined on-site to boilers for facility heating.
  • Comparatively less total primary energy use. Of the five floor coverings considered, solid hardwood flooring uses the least amount of primary energy in manufacturing.
  • Long service life and desirable end-of-life scenarios. Hardwood flooring may be re-cycled or combusted as wood fuel representing an advantage to the environment over other disposal scenarios.
  • Renewable nature of the raw wood input.
  • Carbon neutral benefits associated with wood as a material.

In summary, from an environmental standpoint, hardwood produced in a sustainable manner is an extraordinarily friendly material. According to the American Hardwood Export Council, over its full life cycle, wood releases 24 to 47 percent less air pollution than other flooring products, 8 to 23 percent less solid waste and requires 26 to 57 percent less energy to manufacture. Alternatives discharge as much as 4 times more water pollution and emit 34 to 81percent more greenhouse gas. Wood products originate from a renewable resource - a unique characteristic that gives wood an advantage.

The CORRIM study chronicles solid strip hardwood flooring production from the production of rough kiln dry hardwood lumber at a typical sawmill, through its delivery to the flooring mill, to the point at which it leaves the facility as solid hardwood flooring.

While concluding that wood flooring is relatively environmentally benign across many of its physical attributes, the study did point out a few areas where improvement would be beneficial. Bringing the needed hardwood lumber to final dry moisture content of between 6 and 9 percent was found to be the biggest environmental impact due to volatile organic compounds created and thermal and electrical energy requirements to operate the kilns. Biogenic carbon dioxide resulting from the inventory was much greater than fossil derived carbon dioxide - a plus as biomass carbon dioxide is regarded in many scientific circles to be environmentally neutral.

 

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Originally published in Architectural Record
Originally published in November 2008

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