Eco-Profile of Lumber Produced in the Western United States: Life Cycle Inventory of WWPA Western Lumber

by Scientific Certification Systems, Inc., August 1995. Published by Western Wood Products Association, Yeon Building, 522 SW Fifth Avenue, Portland, OR 97204-2122; 503/224-3930, 503/224-3934 (fax). Spiral bound, 28 pages (not including appendices), $125.

The closer one looks at anything in nature, the more there is to look at. This fact may explain why this life-cycle study of western lumber is both over a year late and much narrower in scope than originally intended. In their attempt to analyze lumber produced by members of the Western Wood Products Association (WWPA) through the strict lens of life-cycle analysis, Scientific Certifications Systems’ (SCS) staff were forced to narrow the scope of their work in several ways.

First, they abandoned the hazy and hard-to-quantify region of environmental impacts and focused strictly on inventories—the quantifiable inputs and outputs of the system. Second, they restricted themselves to the life-cycle stages of resource extraction and product manufacture—not including impacts on the forest ecosystem. Also excluded were inputs and outputs relating to the use and post-use stages of the lumber life cycle. The use stage—the time it is in service in a structure—is too dependent on just how it is used to be accurately predicted. And impacts relating to the ultimate recycling or disposal of the wood after use were not addressed for lack of good data on how much lumber is recycled and what is done with it. In terms of forest products, the study only looks at solid-sawn lumber, both kiln-dried and green.

Within this very narrow scope, SCS researchers appear to have done a remarkably careful study, resulting in data on the inputs and outputs of lumber manufacture with an unprecedented level of reliability. Their work is further substantiated by virtue of having been peer-reviewed by members of the International Standards Organization (ISO) Technical Committee 207 on environmental management.

In energy terms, the results of the study show that kiln-dried wood requires 10.67 megajoules per kilogram

(4,600 Btu/lb) of lumber (at zero-moisture content) for harvesting and processing. Green lumber requires 4.99 MJ/kg (2,150 Btu/lb).

These figures correspond to about 45 MJ (43,000 Btu) for a kiln-dried 2x4 stud of Coast Douglas Fir, and about 21 MJ (20,000 Btu) for the same stud green or air-dried. The difference between the two is primarily in hog fuel (and some natural gas) for the drying kilns. Because hog fuel (chipped wood waste) is a coproduct of the lumber manufacturing process, some would argue that it should not be measured on an equal basis with other fuels. Without the hog-fuel component, energy to make and transport green wood is slightly higher, due to its greater weight. As both the study’s authors and the WWPA rightly point out, these figures should not be used for comparison purposes unless the corresponding figures for the materials being compared use all the same assumptions.

Readers interested in a detailed look at the data should be aware that Appendix B, containing the LCI data tables, is not provided with the report, although summary tables are included. Also, note that Appendix A, which explains how to convert the data from

kilograms of bone-dry wood to actual studs and joists, contains an error. The inventory data should be multiplied by the bone-dry weight of the material, not the actual weight, including the moisture, as the examples indicate.

In not addressing forest ecosystem impacts, the study sidesteps the most important issues relating to wood use and the environment. Those who argue that wood use should be avoided or minimized invariably point to the destruction of old-growth and other forest ecosystems as the primary reason. Others, who believe that wood is a good choice environmentally, point out that working forests can also support wildlife, provide recreation opportunities, and sequester carbon from the atmosphere. Each of these perspectives has some validity, depending largely on the nature of the ecosystem in question and the forest management practices used.

To their credit, WWPA staff recognize this limitation. Bob Petow, executive director of marketing is quoted in the report’s press release as saying: “WWPA recognizes the importance our trade audiences and the general public place on issues not contained within this study’s system boundaries.” While it does not address these critical questions, this new report does provide valuable data on the energy and material inputs and outputs of lumber manufacture. More important, it sets a high standard for future life-cycle inventory studies, in this and other industries.