Improving Wood Products Could Be a Key to Reducing Greenhouse Gas Emissions

Harnessing the ability of wood products to store carbon even after harvest could have a significant effect on greenhouse gas emissions and change commonly accepted forestry practices, a new study from NC State researchers suggests.

The new study published in the journal Carbon Balance and Management uses carbon storage modeling to link the carbon stored in wood products with the specific forest system from which the products originated. Wood products and the forests they come from store different amounts of carbon, and being able to compare the two more specifically would help forest managers better understand these tradeoffs and plan for better carbon storage.

By tracing carbon in southern loblolly pine plantations from planting to harvest, the study also identified specific wood products that are important to improving carbon storage and reducing greenhouse gas emissions. Chief among them were corrugated carboard boxes.

“Corrugated cardboard boxes are one of the most important products made from loblolly pine,” said Sarah Puls, NC State graduate assistant and corresponding author of the study. “If we can extend the effective lifetime of products like these boxes, it could have a significant impact on the carbon storage associated with southern loblolly pine plantations.”

According to the Environmental Protection Agency, these boxes make up 11.4% of all municipal solid waste and account for more than a quarter of all carbon in harvested loblolly and shortleaf pine timber. The study found that improving the lifespan of these boxes and lowering emissions from their production and decay would lead to significant carbon gains from loblolly plantations. Although these boxes already have estimated recycling rates between 91 and 96 percent, increased recycling could still have a significant impact on carbon storage, the researchers say.

The study also found that smaller sawtimber logs and engineered materials like oriented strand board – a type of board made by pressing together small wooden chips – might also be good at storing carbon since they can be grown quickly but still go into long-lasting products like houses.

“Wood is a great material to use in our lives – it’s renewable, it’s very flexible in terms of what we can do with it, and it takes a relatively low amount of fossil fuels to produce,” Puls said. “If we can find ways to keep producing wood while also improving carbon storage – that would be fantastic.”

The study also found that short rotations – harvesting and replanting trees more quickly – could potentially outperform slower long rotations in carbon storage when a forest is highly productive. This finding applied specifically to pulp harvests, which produce the types of wood used in creating corrugated carboard boxes.

Most other research in the field has found that sawtimber harvests outperform pulp in carbon storage. Sawtimber refers to trees which produce the types of straight, thick logs used in construction and furniture. Puls said that even one instance of short rotation pulp harvests outperforming sawtimber was noteworthy.

“Almost everything in the existing body of research says the opposite, that a long rotation strategy is the best for carbon storage,” Puls said. “This implies that we should maybe look at plantations on a more case-by-case basis, and adjust our rotations based on specific site productivity.”

Puls said that the study may help to direct future research around sustainable forestry.

“The bottom line is that we need to take climate action now. This study offers the opportunity for further research, with some specific pointers and suggestions for where we could focus,” she said. “It’s exciting that people are starting to understand that we need to do a better job modeling this, because we need to find ways to better use our forest resources in order to reduce emissions.”

The study was co-authored by Rachel Cook, Justin Baker and Andrew Trlica of NC State University and James Rakestraw of International Paper.

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Note to editors: The abstract of the paper follows.

Modeling wood product carbon flows in southern us pine plantations: implications for carbon storages

Authors: Sarah Puls, Rachel Cook, Justin Baker and Andrew Trlica, NC State University; James Rakestraw, International Paper.

Published Feb. 21 in Carbon Balance and Management

DOI: 10.1186/s13021-024-00254-4

Abstract: Wood products continue to store carbon sequestered in forests after harvest and therefore play an important role in the total carbon storage associated with the forest sector. Trade-offs between carbon sequestration/storage in wood product pools and managed forest systems exist, and in order for forest sector carbon modeling to be meaningful, it must link wood product carbon with the specific forest system from which the products originate and have the ability to incorporate in situ and ex situ carbon synchronously over time. This study uses elements of a life cycle assessment approach, tracing carbon from US southern pine timber harvests to emission, to create a decision support tool that practitioners can use to inform policy design around land- and bioproduct-based mitigation strategies. We estimate that wood products from annual loblolly and shortleaf pine timber harvests across the southern US store 29.7 MtC in the year they enter the market, and 11.4 MtC remain stored after 120 years. We estimate fossil fuel emissions from the procurement, transportation, and manufacturing of these wood products to be 43.3 MtCO 2 e year -1 . We found that composite logs, used to manufacture oriented strand board (OSB), were the most efficient log type for storing carbon, storing around 1.8 times as much carbon as saw logs per tonne of log over 120 years. Results from our analysis suggest that adjusting rotation length based on individual site productivity, reducing methane emissions from landfills, and extending the storage of carbon in key products, such as corrugated boxes, through longer lifespans, higher recycling rates, and less landfill decomposition could result in significant carbon gains. Our results also highlight the benefits of high site productivity to store more carbon in both in situ and ex situ pools and suggest that shorter rotations could be used to optimize carbon storage on sites when productivity is high.