Narratives of Sequestration

Tall Timber

Narratives are central to how society attributes cultural and economic value to architecture. In the United States, there is a long history of seeing residential timber architecture as a type of vernacular practice.1 As early as 1867, the lightweight timber frame was the United States’ contribution to the world’s fair in Paris, where it was described as “decidedly American in its construction—plain, substantial, and convenient—representing thrift and comfort without display.”2 One of the Museum of Modern Art’s earliest architecture shows, The Wooden House in America of 1941, gave timber architecture a genealogy reaching back to the pioneer cabin. By the time of MoMA’s 1948 symposium What is Happening to Modern Architecture?, “redwood” had become a derogatory attribute, bandied about by East Coast critics such as Alfred Barr and Marcel Breuer to disparage the “redwood cottage” style developing on the West Coast.3 Despite this, an alternative form of architectural modernism, critical regionalism, garnered support in the Pacific Northwest as timber architecture became conflated with a particular, forested, cultural landscape.4 Interest in timber architecture has only accelerated in the last ten years. The 2021 US Pavilion at the Venice Architectural Biennale featured a triangular nominal dimension timber frame under the title “American Framing,” and in 2023, the Chicago Architecture Center hosted the exhibition Reframed: The Future of Cities in Wood.

What is new in much of the recent interest in timber architecture is that the focus is no longer on the lightweight frame, nor on situating timber as a vernacular construction type, but on tall, urban, buildings constructed from mass timber. Mass timber draws its name from the German Massivholz, which refers to heavy-framed timber buildings, whether constructed from solid, large timber (as was historically done in the US when there were adequate trees old enough) or produced by laminating smaller pieces together. In its contemporary form, mass timber usually connotes either mass plywood, which is thicker than standard plywood and laminated in alternating orientations such that it can replace concrete core and stair structures; cross-laminated timber (CLT), which also utilizes alternating orientation to increase sheer resistance and act as a slab; or glue-laminated (glulam) beams. It is only through these kinds of fabrication methods that timber can become tall, and it is tallness that shifts timber from a suburban to an urban construction material able to compete with steel and concrete.5

Lever designed NHERI mass timber tower in San Diego built for seismic testing (2023). Credit: Timberlab/FLOR Projects

Millions of dollars are being spent rebranding timber architecture as a sustainable, urban construction type. Every March, Portland becomes briefly synonymous with mass timber when it hosts the International Mass Timber Conference. While the conference is co-produced by the Forest Business Network and the Wood Products Council, there are other industry players invested in this shift. The Softwood Lumber Board (SLB) sponsored the Reframed exhibition, and also funded earlier exhibitions, such as Timber City, at the National Building Museum in Washington, DC.6 The SLB also funds research and development of structural assemblies, seismic resistance, and other products for tall timber buildings: the 2023 Mass Timber Competition “Building to Net-Zero Carbon” offered cash prizes totaling $2.2 million. These efforts are underpinned by the Memorandum of Understanding signed in 2015 between the SLB and the United States Department of Agriculture “to collaborate on market development, research, and technological advances toward expanded use of wood as a natural climate solution.”7

Industry boards are naturally motivated to increase lumber consumption, but there are a number of obstacles that need to be overcome. Firstly, fears for the fire and seismic inadequacy of tall timber buildings, which have little precedent, must be addressed. Indeed, the history of architecture is indebted to devastation wrought by urban fires and spread by timber buildings.8 This suspicion is not limited to the US: building codes in Germany only gradually began to adapt to large timber structures beginning in 2002.9 Research, testing, and development is needed to update construction codes to allow tall timber construction in urban settings. Secondly, from a logistics, planning, and construction perspective, tall timber buildings are more unknown, and thus construction bids for them often come in much higher as general contractors build in margins for error. Material chains and construction logistics are ossified infrastructures that do not easily adapt to change, favoring the production of what is already in place. Depending on the building type and code designation, some mass timber building can be cost neutral based on speed of construction, reduced site work, smaller foundations due to a lighter structure, and by eliminating finishes in favor of exposed structure. However, depending on the contractor, these efficiencies often do not get included in early conceptual estimates. As a result, the tall timber building and the architects who design them need to justify the extra costs. The tall timber building must therefore be situated within compelling cultural narratives that have contemporary valence.

A man being weighed on a set of scales, and a man with his head in a glass container; showing Lavoisier’s experiments with respiration. Drawing attributed to M.A.P. Lavoisier, ca. 1790. Source: Wellcome Collection.

Carbon Commodification

The narrative of the tall timber building has, in the last ten years, become firmly tied to carbon. The typical narrative is that that the more we build with timber (any timber), the more we make a climate-positive impact. This logic is built around the fact that trees participate significantly in the carbon cycle, or how carbon supports plant and animal life by constantly moving between earth, water, and air. Trees breathe in carbon dioxide from the air, store it in every part of the tree (though mostly in the trunk fibers), and breathe out oxygen into the atmosphere. While the group of French chemists Jean Baptiste André Dumas, Jean-Baptiste Boussingault and Antoine Laurent de Lavoisier first described the carbon cycle in the 1840s—quantifying how carbon supports plant and animal life by constantly binding with, and separating from, oxygen as it moved between earth, water, and air—that knowledge long remained a natural process that could inform mankind’s understanding of the world, but not its intervention in it.10 In other words, it was recognized as a cycle long before it became part of a circular “economy.” During the 1990s, however, significant research went into making the interactions of the carbon cycle productive.

The conversation around carbon changed from describing the natural world to designing environmentally-affirmative interventions at the United Nations conferences on the Environment and Development (first in Rio in 1992, then Berlin in 1995). The outcome of those meetings was the Kyoto Protocol, signed in 1997, which included mechanisms to cut greenhouse gas emissions in a cost-efficient manner, such as carbon offsetting.11 developed countries to offset emissions through energy or forest (afforestation and reforestation) projects that mitigate carbon dioxide (CO2) from the atmosphere and allows developing countries to voluntarily participate in efforts to reduce greenhouse gases in return for payments from developed countries.” Emily Boyd, “Governing the Clean Development Mechanism: Global Rhetoric Versus Local Realities in Carbon Sequestration Projects,” Environment and Planning A 41 (2009): 2380-2395.] From this moment on, it was accepted that trees were agents that might counteract the activities through which we otherwise pollute our planetary environment. This effectively separated carbon sequestration from all the other qualities and activities of trees and the ecosystems they are a part of. Calculating environmental damage in terms of carbon emission, perhaps unintentionally, made it possible to elide other types of environmental damage.

Carbon concerns entered the design disciplines most visibly through the “2030 Challenge” issued by American Institute of Architects (AIA) in 2006, which stated that “the urban built environment is responsible for 75% of annual global greenhouse gas emissions: buildings alone account for 39%. Eliminating these emissions is the key to addressing climate change and meeting Paris Climate Agreement targets.”12 The challenge provided guidelines for architects to make fossil fuel energy consumption more efficient, primarily in building operations. In 2006, hopes of reducing carbon dioxide emissions were not yet pinned on using less fossil fuel overall, nor on sequestering it, but on “energy efficiency” that could be achieved “through innovative sustainable design strategies and generating on-site renewable energy.”13

The AIA challenge was aspirational, but vague on implementation. However, efficient carbon use was about to give way to carbon sequestration as a socio-economic force. A panel held the following year at the annual conference of the American Association of Geographers titled “Theorizing the Carbon Economy” began to articulate the ramifications of making trees’ abilities to sequester carbon part of an economic network, in particular, of using trees to offset other environmental damages. The papers presented were published as a special issue of Environment and Planning A in 2009. The issue is one of the first clear articulations of what issues might arise when carbon stored in forests is commandeered into an economic network at the scale of the planet and what problems might result from carbon’s commodification.

The editors recognized the urgent need of mitigating climate change by way of using trees to sequester carbon, but identified several roadblocks to implementation. Of these, the most pressing challenges were to define what the aims of a carbon economy were, and that, whatever these aims were, the carbon economy should be established scientifically rather than through unregulated carbon speculation.14 There was no agreement, however, on what the carbon economy was, or how to map it and intervene into it. Emily Boyd, for instance, examined afforestation projects implemented by partnerships between European countries and private companies in Latin America, where significant problems on the ground muddied the abstract, pre-design carbon calculations reckoned in the West. Boyd also proposed that thinking the carbon “problem” at the global scale was itself a major risk to carbon’s rebranding as economic player.15

In 2010, the issue of carbon sequestration entered the architectural discipline by way of planning. That year, a special issue of the Journal of the American Planning Association, edited by Randall Crane and John Landis and titled “Planning for Climate Change: Assessing Progress and Challenges,” interrogated what the planning discipline might offer urban settlements in adapting to climate change in the face of insufficient national-level mitigation efforts. In the issue, Thomas L. Daniels evaluated how forest management strategies could contribute positively to climate concerns, neither as mitigation nor adaptation, but as offsets. He reflected on how carbon sequestration in forests might contribute to political discussions and economic calculations around carbon emission cap-and-trade models. In floating the idea that, instead of reducing carbon-based emissions, forests could counteract them, Daniels’s argument nonetheless highlighted the difficulties of calculating how carbon credit trading schemes could pay foresters to continue doing exactly what they were already doing.16 Around the same time, in positing a carbon cycle model to include forests, another study noted the problems with standardizing carbon accounting as it moved between forests and forest products: “how far down the product chain the model extends is yet to be determined, but for now it should at least consider the use of wood products that substitute for more carbon-intensive products.”17

Patrick Fleming, Simon Smith, and Michael Ramage’s 2012 article on mid- and high-rise timber building design argues for building with laminated timbers in a way that resembles how we discuss mass timber today: “[R]ising concerns of climate change and the carbon-dioxide emissions associated with construction encourage the use of wood as a viable alternative to steel and concrete, due to CO2 sequestration in trees.”18 But searching the Avery Index of Architectural periodicals, it is only from 2014 that articles about buildings begin to pair terms “carbon” and “sequestration,” which is coincidentally the same year that the Softwood Lumber Board began sponsoring the US Tall Wood Building Prize.19 In the ten years since, however, publications, news articles, and exhibitions have increasingly begun to situate the tall, mass timber building squarely in the carbon sequestration narrative.20

The pressure to quantify the value that building with timber might bring to our built environment binds the tall timber building to the carbon economy, to the abstraction of the carbon cycle, and to counting carbon. This happens in the form of models that calculate the carbon costs of the material chain from forest to frame and landfill in various ways. But it also happens through forest inventories, like Oregon’s Forest Resources Institute August 2022 Carbon in Oregon’s Managed Forests. On Earth Day 2022, United States President Joe Biden called for a carbon inventory of all forests on federal land in the United States. On Earth Day 2023, the Forest Service and the Bureau of Land Management announced that “more than 100 million acres of mature and old-growth trees are standing on federal lands—trees that play an outsized role in conserving wildlife, purifying our water, and stabilizing our climate.”21 In this way, buildings and forests have become subject to the same strategies of carbon accumulation. But inventorying existing carbon is a rough science at best, and there are parts of a forest that cannot be counted. The limits of the model is a significant design decisionthat impacts what, in the supply and product chain, is included and what gets left out. As a result, like in all timber narratives before it, there is at times a disconnect between what architecture says about timber and what industrial forestry is doing with trees.22

Visual investigation of the active transfer of accumulated carbon from a decaying nurse log into the next generation of forest life. Alexandra Kiss, Forest Nurse Figure-Ground Diptych (2023), 41”x33”, acrylic gouache on paper and digital collage. ©Alexandra Kiss

Beyond the Limits of the Model

In the forest along the Old Salmon River in Oregon, the prostrate nurse log indexes a protracted historical event. Aging, perhaps structurally weakened, she snapped in a winter windstorm around 1840.23 As she fell, she took down several smaller trees, flattened the undergrowth, and disturbed the soil. She shattered into smaller pieces, but most of her vast length settled into place as a horizontal, dying tree. She initially would have lain straight, the carbon in her fiber helping hold her prone above the depressions in the ground like a bridge. But, over time, she began to sag and deform. Because what remains of that forest has since been protected as the Mount Hood National Forest, she remains today, but it is hard to distinguish her from the surrounding growth and undergrowth. Decaying, she has become a catalyst for new life. New trees have sprouted from her trunk. In another hundred years, maybe all that will be noticeable of her is a squishy, mossy surface. Her ghost will be seen only in the straight line of trees that grew out of her.

In US silviculture terminology, the nurse log is a large piece of coarse wood on the forest floor that is referred to as fallen, debris, or dead. Nurse logs render the difference between plantation and forest visible. Nurse logs do not exist in industrial forestry, where the ground is raised by heavy machinery, where undergrowth is cleared to protect against the fire and disease that spread more easily in single-species plantations, and where insecticides are sprayed to prevent the growth of less economically-viable species. As debris, the nurse log represents for industrial forestry an economic inefficiency. But the common term, “nurse log,” contradicts this, highlighting the difference between dead, an adjective, and dying, a verb. As she slowly decomposes, the nurse log emits carbon as carbon dioxide not just into the atmosphere, but also into the soil, where it serves as sugar for other trees. As a mother, she nurses new forest life as she dies. The nurse log delays carbon release, which is important since the longer the carbon is stored, the better. Her carbon release also brings other environmental benefits. There are some species of smaller insects that only feed on certain dying tree species. The closer we look, the more the nurse log becomes a process, not a thing that can be counted. At the scale of leaves and lenticels, the boundary between the nurse log and the life she supports disappears, connected physically, chemically, and visually to her surroundings as one enormous organic composition.

Recognizing the friction between the nurse log as dead—as debris—and as dying—as process—brings to our attention the issues involved in converting the value of a tree into a quantity of carbon. Dead, unable to actively capture carbon dioxide, she represents a carbon loss. Beyond representing the antithesis of industrial forestry and holding no exchange value, dead, she also offers no value in architecture’s carbon narrative. Carbon counting tries to quantify the nurse log’s carbon, or give static form to her presence. Dying, however, she supports dynamic worlds that rub up against the simplicity of carbon equations. The benefits she offers to our air, our water, and our non-human partners on Earth are beyond carbon.

The simplified view present in many carbon models—as well as architectural and wood product accounting—that living, growing trees sequester carbon and dead, decomposing trees release carbon, doesn’t account for time. Certainly, when a tree stops living, the process of absorbing carbon halts, and carbon begins to be released as carbon dioxide. Whether it is cut down or falls, the logging or blowdown will cause carbon to be released into the air. But when a tree is transformed into lumber, we say the carbon is sequestered. This is never permanent, however; it is merely the delay of a natural process. A building’s lumber will only continue to store carbon until the day that lumber is inevitably replaced or the building demolished. When the lumber in the building ends up being burned for fuel at the end of its life, or placed in a landfill to decompose, all the carbon it stores will end up reuniting with oxygen to become carbon dioxide. Greenhouse gas emissions have simply been delayed.24

Delay, again, falls out of many carbon counting schemes. Carbon is constantly moving and wood is constantly breathing in or out, even as it dies. The nurse log highlights this. But most carbon substitution schemes assume carbon as fixed: as either in trees or in buildings. With wood, the only temporarily “fixed” moment is when it is preserved as construction timber for a relatively short period of time. What matters for climate change mitigation is the rate of carbon transfer between benefits and losses (inputs and outputs). To reduce atmospheric carbon, more trees need to be planted than are cut down to make buildings. If we consider wood alone, plant a million trees, and use those million new trees to build timber cities, by the time those buildings come down, we will have made approximately zero change to the quantity of carbon dioxide being emitted on our planet. And that does not account for the carbon dioxide used to process those trees into wood, to transport them to where they are going (which may be halfway around the planet if the supply chain proves cheaper), to assemble them, and to disassemble them—let alone the fact that it will take decades for any replanted trees to grow big enough to store enough carbon to replace those that were removed.25 And for many calculations to work, other buildings built from other materials must not be built: using wood as a substitution for other materials is part of the narrative, and thus requires performing the entire calculation for the other buildings that tall timber buildings will replace. Either way, an approach to building that assumes trees live, and timber buildings last, longer is a critical step in slowing down cycles of carbon transfer.

The nurse log is an indicator of what fits into a carbon ecology but not into a carbon economy. She holds sequestered carbon, but her value is delay, not accumulation. This is not to suggest that using carbon to measure the environmental impact of different forms of construction is irrelevant. The more that the building industry can shift from using finite resources and materials with high embodied energy, like concrete, aluminum, and steel, to renewable materials, like timber, earth, or fibers, the better. But this is not the only issue at stake. By marrying itself to the carbon narrative, tall timber buildings run the risk of eliding their other impacts. As compelling as it is for industry, talking and writing about timber buildings only as sequestered carbon risks making the claim that all timber buildings have a carbon positive impact (and are thus are a “climate solution”) by oversimplifying carbon counting; that all wood is good wood (and thus using it is beneficial for the planet’s ecosystems); and that our forest resources have the capacity to accommodate a scaling-up of timber-based construction in an environmentally-positive way.

Timber can have an important role to play in a more environmentally-positive future for the construction industry—if, that is, decelerating our construction habits and building less single-family houses is also a part of the future we value. But the narrative that building with timber is automatically environmentally positive because timber stores carbon dangerously simplifies the host of ethical choices that arise in material specification. By pinning the narrative of timber’s sustainability to carbon, architects risk transforming forests-as-ecosystems into forests-as-plantations. We risk encouraging the ecologically damaging practices involved in industrial forestry, such as the use of pesticides, the increased vulnerability of single-species plantations, the pollution of water sources, or the destruction of less economically valuable local species such as oak or hemlock in favor of the fast-growing money tree, the Douglas fir. Architectural discourse can impact construction culture, and therefore forest management, by designing more nuanced narratives for timber beyond carbon.26

(Left) ZGF Architects, Wooden roof installed in its final location at the airport. Credit: Port of Portland/ZGF Architects. (Right) Marked wood logs for transport from the Skokomish Tribe forest. Credit: Port of Portland/Hannah Letinich.

Good Wood

There are many foresters in Oregon who are trying to encourage healthy ecosystems instead of only growing a stand of 2x4s for dimensional framing. These include Indigenous forest owners, small family foresters, and variable retention foresters who practice selective cutting, and who consider the forest a gift that we have a responsibility towards rather than a resource to be owned. Even some larger private landowners are participating in slightly less intensive models of forestry than the industrial model through participation in habitat conservation plans and improved forest management (IFM) carbon projects. They see a place for the non-financially lucrative parts of a forest while keeping the system productive and economically viable. Together with a growing number of architects and historians, they are beginning to call what they produce “good wood,” for lack of a better terminology or parameters beyond Forest Stewardship Council (FSC) certification.

There are two main problems for architects and clients who try to use “good wood.” Firstly, how do we know what “good wood” is, and, secondly, how does it get to the construction site? The new Portland Airport expansion project, which includes a long-span mass timber roof designed by ZGF Architects and structural engineers KPFF, is an example of this struggle, and pioneers a new kind of responsible, regional, practice. It is the result of years of research articulating what good wood is and how to procure it. Working between different definitions and practices of sustainability and getting to know how foresters themselves aim to keep their forests healthy led ZGF to develop a custom wood sourcing criteria that focused on cultivating ecological forestry, supporting underrepresented landowners in the supply chain, and exploring what climate smart and resilient wood can be. The criteria was made up of multiple procurement and forestry-based pathways that aimed to reward foresters going beyond the legal minimum requirements, while also being more inclusive than market-based third-party certifications. The resulting Wood Procurement Performance Criteria requires wood to come (1) from within a 600-mile radius of the work site; (2) from multi-age forests that meaningfully include native species and harvest rotation; (3) from forests that employ variable-retention and encourage ecological complexity; (4) from forests that emphasize complexity in thinning, and, consequently, on modifying understory, midstory, and overstory conditions; (5) from forests where defective trees and structures (e.g., snags, logs, cavities, and brooms) are retained; and (6) where risks such as insect infestation, fungus, or fire, is minimized through species complexity. Additionally, the criteria required that no more than 375,000 gross board feet come from any one landowner. Parameters such as these also define what a “region” is in a productive and meaningful way.

Defining good wood is one thing, but how to get that wood from the forest into the building is another. Between the forest and the designer’s desk stands an opaque chain of custody, making it practically impossible to track wood. The logic that drives industrial forestry’s material chain in the Pacific Northwest originated in the lumber mill a century and a half ago. In the early nineteenth century, at the hands of merchant loggers, stands of Sitka spruce, Douglas fir, and western red cedar on the coastline north of San Francisco became ballast for ships trading logs within a sophisticated mercantile network between Japan, China, Hawai’i, Chile, and Australia.27 The lumber mill was born as a mercantile operation, not as a service provider, built merely to turn trees into transportable commodities.

Today, still centrally located in the timber material chain, the mill does not differentiate where the wood it turns into dimension lumber comes from. It procures logs from a particular forest through a timber sale, then sorts these logs into piles of similar quality. When the timber market justifies it, the mill turns these logs into graded, but placeless, commodities, most commonly 2x4 framing lumber.28 The mill, in this sense, becomes a speculative mediator between a forest cycle and the housing market. It would take little physical restructuring to keep wood from sustainable forests in a separate pile at a mill, or to run this wood through the milling machinery separately from other logs. But it would generate multiple inefficiencies and resistances in an ossified and intransigent infrastructure built upon the premise that the mill values efficiency over everything else, and that it is a merchant and not a service provider.

The shutdown of global trade that resulted from the Covid-19 pandemic revealed that many kinds of companies did not know where the component pieces of their products were made and what kinds of supply problems, political issues, labor conditions, or environmental impacts were built in to them.29 Material chain transparency, it turned out, was necessary for companies to manage complex supply chains, and is also now being demanded by consumers interested in making ethical choices. This change builds upon developments such as the Transparency in Supply Chains Act, enacted in 2010 by the California state legislature, which aimed at making visible the unethical labor conditions and human trafficking embedded in supply chains to make products cheaper.30

Construction materials are beginning to enter this conversation. There are tools that have come on the market in the last few years that attempt to track the timber material supply chain, like Preferred by Nature’s Timber Chain, which tracks where lumber is as it moves between the forest and the hardware store. In January 2023, IKEA published its own wood supply maps, documenting not just how much lumber comes from what parts of the globe, but also what species of tree are used, whether or not the forests are FSC certified, and any concerns such as illegal logging or environmental impact that they encounter in those exchanges.31 Likewise, LEED’s Timber Traceability Pilot Credits aim for transparency to guard against illegally logged wood.32

Material chain transparency sounds simple. But turning trees into CLT involves at minimum a forester, a logger, a log truck driver, a lumber mill, a buyer, a product manufacturer, a timber sales representative, a specifications writer, a contractor, a team of architects, and a client. The ramifications of transparency for the material chain are immense; it questions the very logic of the US lumber mill as it has operated for industrial forestry throughout history. In an attempt to help standardize the ask from the design industry for wood transparency, ZGF has been working with SERA architects, the Climate Smart Wood Group, and other specifications writers to develop a publicly available Wood Supply Chain Transparency Specification. The package will include template specification language, reporting forms, and implementation guidance to help advance transparency and disclosure in the wood supply chain all the way back to the landowner and log sources.33

Forest to frame map showing the forests of origin for PDX, lumber mills, and timber fabricators. Credit: Port of Portland

When the Portland Airport extension project began, however, none of this was in place. ZGF principal Jacob Dunn worked with Paul Vanderford and Ryan Temple at Sustainable Northwest Wood to help engage the supply chain, write a reasonable specification, and navigate this non-standard procurement process. This entailed working with mills to help identify compliant harvests, and in some cases advocating for bidding higher on certain lumber sales that met all of the project’s criteria. They also facilitated conversations between the project’s contractors (Hoffman/Skanska and Timberlab) and lumber mills to plan custom batch runs for segregated logs outside of normal production. Instead of residing on the typical claim of knowing their wood comes from a state or larger region like the Pacific Northwest, the Port of Portland produced a “Forest to Frame” map, whose graphic simplicity belies the incredible effort it took to make the material chain visible. With it, they can show exactly who their wood came from for the roughly 1,000,000 board feet of wood that utilized these transparent procurement approaches (approximately 40% of the overall 2.6 million board feet in the roof’s curved glulam beams and ceiling timbers).

As a result, the port can now tell the story of who and how the wood was harvested across the thirteen local landowners within the region, including small family forests, three different tribes, non-profits, or University forests practicing best in class forest restoration or ecological forestry. These stories span knowing why the hazard trees came down around the hiking trails for the Chimacum Community forest, how the natural resource revenue from single-tree restoration is helping the Skokomish tribe consolidate forest allotments to bring more of their forest under tribal management, how Hyla woods is pioneering forestry models for small foresters that balance both economy and ecology, and how the Nature Conservancy’s Cle Elum operation is revitalizing rural communities while reintroducing fire back to their forests to make them more resilient. The PDX project was special in terms of its aspirations and ability to devote resources to the sourcing effort. For now, all this work has to be repeated in every project by every architecture firm that wants to answer the question “where does your wood comes from?” But the efforts made by ZGF and the Port of Portland project team make it possible to imagine this process becoming regionally streamlined in the future, and to imagine a regional architecture that embraces the sustainability and equity of its supply chain.

Portland Airport’s wood procurement policies shift the scale of forestry from a national affair supported by opaque, long-distance material supply chains to a regional, circular economy where each part of the supply chain is a relationship rather than a transaction. It highlights that ecological responsibility might benefit from shrinking the scale of US forestry management.34 But if US forestry might benefit from a more regional approach to management, the picture of carbon accounting could do with some enlargement.35 The boundaries of carbon models need to be examined, and designed to encompass more than just forest products. If we cannot track where the wood came from, it is not easy to calculate the carbon used in the procuring it. Architects building with timber have a role to play in bringing about the cultural changes necessary for developing ecological forestry practices, but it all starts from collectively asking where our wood comes from, and what the environmental impact of that forest’s management plan are. Calculations are only as good as what we know, and beyond carbon, any positive impact regarding material choices must be related to what costs we allow to be externalized. As compelling as the carbon narrative is, we should consider accumulating not only carbon through architectural design, but also knowledge about the forests we use.