Understanding the utility and limitations of Life Cycle Assessment (LCA) and Environmental Product Declarations (EPDs) for wood products is fundamental.

LCA is a method for quantifying the environmental impacts of a product or an entire building project throughout its life cycle. During the procurement process, EPDs are increasingly used to gather data on a specific material or product.

EPDs are independently-verified LCAs that report on a range of environmental impacts, including global warming potential, acidification, eutrophication, and others. In particular, when LCA studies are conducted for individual companies and the results are reported in product-specific or supply-chain specific EPDs, it is possible to compare the carbon footprint of competing products of the same type. This allows purchasers to select the product that has the smallest footprint and feed that information into Whole Building LCAs in pursuit of reducing a building’s overall embodied carbon.

Why then doesn’t CSWG’s guidance include LCAs and EPDs as a procurement option for CSW?

The answer is that while EPDs can be used to compare emissions associated with manufacturing and transporting a product, EPDs do not report on “climate smartness” of wood products, or any other building material, in part because most forestry activities and land management operations are not included in these models.

Additionally, climate smart forestry is about more than carbon accounting.

CSF also aims to increase the health and resilience of forests, and includes techniques that address climate mitigation, adaptation and equity. While EPDs are a robust tool for understanding some facets of environmental impact, they do not measure broader ecological metrics such as biodiversity, ecological health, or environmental justice. Current LCA methods used in the forest sector do not directly account for changes in forest carbon stocks resulting from specific forest management activities that occur across managed landscapes over time.

As a result, contemporary EPDs for wood products do not reflect or acknowledge carbon gains or losses that are actually occurring in specific managed forests. Instead, nearly all North American wood EPDsadopt the “biogenic carbon neutrality assumption” which assumes carbon gains from forest regrowth in a managed area are exactly equal to the amount of carbon stored in forest soils, logging slash (branches, leaves and needles), and roots that will be emitted through decay or be burned post-harvest as well as the amount of carbon removed from the forest in the form of harvested logs.[1] This assumption is often invoked so that emissions of “biogenic carbon” that occur during the processing of logs into finished products can be conservatively ignored.[2]

According to current LCA Standards, any manufacturer or supplier can use the carbon neutrality assumption if the wood comes from a “sustainably managed forest,” a phrase which is generally understood to mean “forest with stable or increasing carbon stocks.”

Most wood EPDs invoke the carbon neutrality assumption due to carbon stock estimates at a national scale (e.g. the overall forest stock across the entire US is generally agreed to be stable or increasing, including both actively managed, and unmanaged or non-commercial forestland). [3]

However, this assumption, particularly when applied at regional and continental scales, obscures the critical underlying reality that no forest is exactly carbon neutral regardless of whether it is deemed to be “sustainably” managed. The shortcomings of this assumption and the scale at which it has been widely applied offered the primary motivation for the CSWG to address Forest Carbon Stock  accounting approaches.[4] Because the “biogenic carbon neutrality” assumption treats all “sustainably managed forests” as carbon neutral, it eliminates any ability to differentiate timber suppliers or timber supply areas based on observable differences in carbon stocks that accrue on landscapes being managed differently over time.

Considering many forest owners are intentionally increasing carbon stocks as a CSF strategy while others may have flat or decreasing carbon stocks in their forests over time, estimating the carbon stock change of a specific woodshed and allocating this value to a wood product coming off of that landscape is a promising approach to quantifying the carbon implications of a wood product.

This approach, currently in development, attempts to correct for the fact that this benefit (or burden) is currently ignored in product-specific EPDs given local and regional data suitable for this purpose are publicly available.

Through the lens of LCA, wood products from forests that represent a wide variety of management practices and starting conditions are treated the same – the only differences captured are in emissions resulting from a given company’s use of energy and fossil fuels in timber harvest and downstream manufacturing and transportation. Yet, the carbon benefit of CSF can easily outweigh all other factors combined. In other words, current LCAs and EPDs for wood provide no advantage for companies that practice or source wood from CSF, and thus they have limited relevance in CSWG’s procurement guidance.

LCAs and product-specific EPDs for materials other than wood promote internal competition among companies within the industry in question to reduce their net emissions. However, the assumption of forest carbon neutrality blunts this effect in the forest products industry.

Research on improving LCA methodology to address this blind spot is underway, and CSWG guidance will change when science-based methods for factoring forest carbon stock changes into LCAs and translating those changes into EPDs for wood products are developed.

[1] Of a living tree’s total biomass, about 40-55% (hardwoods) and 50-55% (softwoods) is contained in the “merchantable” portion that would ultimately enter a sawmill. The remainder of the tree’s biomass is contained in its fine roots, stump, branches, bark, and top of the tree, which are generally left on-site to decay or are burned following timber harvests. These ratios are drawn from: Jenkins, J. et al. (2004). “Comprehensive Database of Diameter-Based Biomass Regressions for North American Tree Species.” NE-GTR-319. U.S. Department of Agriculture, Forest Service, Northeastern Research Station: Newtown Square, PA: 45pp. https://doi.org/10.2737/NE-GTR-319 and Cairns, M. et al. (1997). “Root Biomass Allocation in the World’s Upland Forests.” Oecologia 111(1): 1-11. https://doi.org/10.1007/s004420050201

[2] The process of converting logs into finished products retains a fraction of the carbon in the log, with half or more of the carbon in logs commonly transformed into waste or by-products (e.g., chips or sawdust) which have short lifespans and are often combusted for heat and/or energy during manufacturing. For example, the “recovery ratio” for producing softwood lumber from logs in the Pacific Northwest was estimated at 0.505 m3 lumber per m3 of logs: Milota, Mike. (2015). “CORRIM REPORT: Module B Life Cycle Assessment for the Production of Pacific Northwest Softwood Lumber.” CORRIM: Seattle, WA. 73pp. https://corrim.org/wp-content/uploads/Module-B-PNW-Lumber.pdf.

[3] Placeholder to add some additional citations.

[4] The approach to accounting for the “upstream” carbon impact for biomass products such as wood is described in: Johnson, Eric. (2009) “Goodbye to Carbon Neutral: Getting Biomass Footprints Right.” Environmental Impact Assessment Review: 29(3): 165–68. https://doi.org/10.1016/j.eiar.2008.11.002