Big trees, tall buildings: How forests can help solve global warming through carbon storage

Editor’s Note: In a three-part series starting today, Treesource will explore the potential roles of forests and wood products in addressing the global climate crisis. 

Part 1: How can we use more wood, a renewable, biodegradable carbon sink, while also storing more carbon in forests across the U.S. and the world? 

Part 2: A detailed look at the policy choices that governments, businesses and individuals must make. 

Part 3: A look ahead to 2050. What could a more sustainable society look like, if forests and wood products were utilized in new ways?

In 2018, the Intergovernmental Panel on Climate Change issued a warning that one United Nations official called “a deafening, piercing smoke alarm going off in the kitchen.” For the world to avoid ecological and social catastrophe, the scientists said, humans must quickly and radically transform the systems that provide energy –- by ceasing to burn fossil fuels. Greenhouse gas emissions, they said, must drop by half no later than 2030, and to zero by 2050.

Three years later, in August 2021, the IPCC returned with what the UN’s secretary general labeled “a code red for humanity.” The wildfires, droughts, hurricanes and brutal cold snaps of recent years were evidence that so much carbon dioxide is already cooking the atmosphere that further calamities are inevitable.

And yet, the significant curtailment so urgently needed has not happened. Instead, greenhouse gas emissions actually increased between 2018 and 2021, the IPCC said.

Action is needed.

Now.

On many fronts.

In addition to phasing out fossil carbon, one of the remedies consistently mentioned by the IPCC – and gaining heightened attention in recent years – is “natural carbon storage.” The capture and storage of carbon through natural processes in the soil, wetlands, forests and wood products –- followed by its monetization –- began more than 20 years ago. Now, with corporate and organizational pledges of “net-zero” emissions growing by the week, groups are scrambling for ways to accomplish those goals. Natural carbon storage is part of the answer, said Jad Daley, CEO of American Forests, the oldest forest conservation organization in the U.S.

Daley explained: “Imagine we have this ‘magical device’ that can suck carbon dioxide out of the air and give us back oxygen, while storing the carbon in a form that provides wildlife habitat, a water filtration and storage system, a renewable, biodegradable building and packaging material. … Oh, we don’t have to imagine it, we already have trees in forests.” In fact, Daley believes the world is entering a heyday of intensive forest rejuvenation and increased wood-products use in response to global warming. Both, he said, are possible.

The science of forest growth provides evidence of the potential to produce more wood and to store more carbon by instituting longer growing periods between timber harvests, and by using different practices to grow and store more carbon in the forest. At the same time, researchers believe cities and nations could emit less carbon by using wood as a building material rather than concrete, steel, brick, aluminum or other energy/carbon-intensive products.

The challenge, of course, is how to grow more trees and use more wood simultaneously, said Barry Ulrich, director of The Nature Conservancy’s American Forest Carbon Initiative. “Nothing we are doing is designed to cut out the [wood products] industry; it is not about stopping harvesting. It is about doing it (capturing more carbon and more wood) sustainably. … The transition to doing both is the challenge.”

Antony Wood, CEO of the Tall Building and Urban Habitat Council, was a keynote speaker at the International Mass Timber Conference in spring 2021, during which he presented his vision of cities as carbon sinks. A metropolis stores carbon when wood is used for the built environment, he said, rather than the concrete and steel favored for more than a century. But greater utilization of wood products necessarily means increased timber cutting and milling.

In 2017, The Nature Conservancy led an international team of scientists to determine how much natural carbon storage is attainable and what actions would have the greatest positive impact.

In 2018, a second paper assessed the carbon storage potential of U.S. forests. The report’s conclusion: It would be ecologically possible to increase the use of forests for carbon storage while also boosting timber harvests for the construction of “carbon sink” cities.

“We can absolutely do both while making our forests more resilient to the changing climatic conditions,” said Daley at American Forests. “But we have to recognize that techniques for forests in Vermont and in Arizona will be very different, so the policy framework to accomplish these goals needs to be planned and implemented locally.”

Wood products were not addressed directly in The Nature Conservancy paper, but harvesting to meet the needs of people for construction materials, furniture, packaging, paper, energy was acknowledged as necessary. Said TNC’s Ulrich: “The potential benefits of using wood, like cross-laminated timber and other forms of mass timber, for creating wood-based mid- and high-rise structures in cities worldwide are substantial.”

Joe Fargione, lead TNC author of the U.S.-focused paper, modeled a variety of techniques to show the magnitude of potential benefits. Forests in the U.S. have captured and stored 12% to 15% of domestic fossil-carbon emissions for more than 50 years. How much more could be stored, Fargione asked, if the nation launched a full-scale effort? The answer: another 20%.

The combination of existing and potential natural carbon storage projects could capture one-third of the United States’ greenhouse gas emissions problem, according to the TNC report. The remaining two-thirds must come from reducing fossil-fuel emissions or via technological carbon capture and storage. Direct air capture is one example, but is phenomenally expensive at present.

Forests provide the greatest natural carbon storage potential, through planting new trees, growing existing stands longer between harvests and improved forest management practices. Said Fargione: “Certainly, there is opportunity to do targeted thinning to protect forests that are the most out of whack from a fire-regime standpoint or where watersheds or old-growth forests are threatened.” TNC advocates “thinning and burning in combination to accomplish restoration of the forest,” or so-called “carbon defense,” he said.

To address the entire country and its diverse forest ecosystems, a number of simplifying assumptions were necessary for the TNC-led analysis. For example, the team assumed that all “natural forest management” lands would see a harvesting hiatus for 25 years. At the end of that period, the resulting larger-diameter trees would have stored more carbon – but also would provide more wood. In addition, the rotation age of intensively managed forests (primarily in the Southeast and Pacific Northwest) would be extended.

Fargione acknowledged that the condition of the land in various regions would dictate the actual management actions. The “devil is in the details,” he said. There is no one-size-fits-all approach, but it is difficult to model all the different possible forest treatments in one nationwide study.

Christine Cadigan manages the Family Forest Carbon Program for the American Forest Foundation (AFF). The program is a joint project of AFF and TNC, targeting the smaller forest landowners who represent about 38% of all forest land nationwide and who offer a major opportunity for more carbon capture. However, these small forest lands also represent about half the log supply for domestic sawmills. Thus, the Family Forest Carbon Program, which is intended to wrestle with the devil in the local details – the sweet spot where a landowner can provide logs, store more carbon, create wildlife habitat and protect water quality. Meeting such divergent goals takes a lot of work and solid partners in research: at TNC, universities, the U.S. Forest Service, practitioners and landowners. “As we develop the practices, we always keep those conservation goals in mind,” Cadigan said. “We won’t adopt practices that have a carbon benefit but don’t also meet those other conservation goals.”

As scientists and program managers dive into the details, they are finding opportunities to accomplish a combination of goals – but again, the methods vary by forest ecosystem and region. In Eastern hardwood forests, for example, landowners must create openings in the forest.

In the 1990s, New Jersey Audubon and others found that neotropical birds were declining in number in the northern forests where they migrate to breed.

One of the major culprits: lack of foraging habitat.

One of the answers: more harvesting to improve avian habitat, while also providing logs for regional manufacturers.

Where do carbon offsets figure into the picture? For two decades, carbon offset programs have focused on large ownerships because of the expensive verification and measurement requirements borne by landowners. The contracts often required a 100-year term, more than the owners of small tracts are willing to consider. The Family Forest Carbon Program takes a different approach, focusing on carbon increase over time rather than on a forest’s existing carbon. Therefore, they pay landowners to implement practices that will increase the amount of carbon stored over a shorter period, say 10 to 20 years.

Ullrich stressed: “Carbon offset sales require an intensive vetting process, during which corporations can show they are first reducing their operational emissions.”

Forest management is also modified. Practices tested in central Appalachia include a prohibition on “high-grading,” a practice that allows bigger trees and more valuable species to be harvested and the rest to be left behind. Cadigan said high-grading can result in a shift away from oak, hickory, walnut and cherry trees, which provide valuable lumber and excellent food for wildlife. By working with landowners to modify harvests to retain some of those larger trees and provide seeds for a new forest, these species will continue to grow and store carbon –- and, in time, provide valuable logs.

The financial part of the bargain involves carbon offsets –- paying forest owners upfront for some of the carbon they will store and paying for more carbon later. The landowner can still sell some of the trees and thereby create desired habitat, while the modified harvest method produces more carbon and manufacturers get logs. This approach, along with Fargione’s example of “defensive carbon management” to reduce wildfire severity and insect risk, are just two of many practices where the multiple goals of carbon storage, healthy forests, wildlife habitat, wood production and watershed protection can be synergistic.

How carbon offset markets are structured and the potential for unintended consequences cause some forest owners and wood manufacturers to be cautious. One of those is Paul McKenzie, the vice president and general manager for F.H. Stoltze Land and Lumber, a 109-year-old company in northwest Montana. Stoltze has almost 40,000 acres in timber management, as well as a sawmill that is fed from its own land and a collection of small private, state and federal lands.

McKenzie worries that paying a landowner to leave the forest untouched for 10, 20, or 30-plus years has significant risks. He explained: “The national forests in Montana have become a carbon source rather than a sink because of mismanagement over the past 30 years. Bark beetle epidemics and severe wildfires have killed extensive areas. … Not only that, but the mills would go away unless there is another source of logs.”

What is needed, McKenzie said, is more markets for the smaller trees that need to be thinned from overcrowded Western forests – and which could be used to store carbon in wood products for longer periods. Stoltze has embarked on one such effort.

McKenzie stressed: “We can’t look at carbon and forests with tunnel vision. Forests provide habitat for wildlife, serve as water storage and filtration systems (some of Stoltze’s lands are under a conservation easement to protect the city of Whitefish’s water supply), provide a sustainable supply of renewable, biodegradable products and store carbon in the trees and the products.” The design of any carbon market should strive to avoid unintended consequences, he said.

McKenzie would like to tie the carbon revenue stream to actions that make the forest healthier – more resilient and more resistant to disturbances. And he said he likes the concept behind the pilot project in Pennsylvania by the American Forest Foundation, which is expanding to the Upper Midwest and Northeast, where payments are tied to better forest management practices that produce more carbon. That link can lead to better overall forest management to meet landowner objectives and carbon objectives, McKenzie said. “History has shown us when we focus too narrowly, we get in trouble,” he added.

Katie Fernholz, president of Dovetail Inc., a consulting forestry firm and think tank based in Minnesota, provides a more optimistic outlook. Can the U.S. grow and store more carbon while also harvesting more timber? “Yes!” she said,” if we do it carefully, using our scientific knowledge. We must tailor the methods and practices to the forest ecosystem, land ownership goals and robust policy that avoids the unintended consequences.”

Coming next: In Part 2 of this three-part series, Treesource will explore the ways to carefully use forests as carbon sinks while expanding timber harvests and the use of wood in built environments. What policies and investments can and should be made to create incentives for natural carbon storage?