Absorption in the Landscape

By Tim Kerner, AIA 

Atmospheric carbon has swelled and ebbed over geological time. Photosynthesis, respiration, decomposition and emissions all play a role in the earth’s fluctuating carbon cycle. Over the past two hundred years, humans have made great efforts to destabilize this system. We extracted carbon from the ground that took millions of years to accumulate and combusted it into the atmosphere, we stripped away forests and wetlands that are essential carbon absorbers, and we created settlement patterns and lifestyles that depend on vast expenditures of fossil fuels.  

Now we need to think differently. In addition to reducing the carbon emissions associated with building construction and operation, architects need to look beyond their structures and consider the carbon absorption possibilities of the surroundings. Our landscapes offer an array of opportunities to make the places we live, work, and learn essential allies in the fight to reduce atmospheric carbon and mitigate climate change. Ecosystem biodiversity and connectivity are at the root of this strategy. 

Civilization emits more carbon dioxide each year than can be absorbed by all the plants and oceans of the world. Levels of atmospheric carbon are now 40 percent higher than at the start of the industrial revolution.1 And despite international agreements, human generated emissions continue to rise. Over the past 40 years, annual global greenhouse gas emissions have increased by 67 percent.2 We are now witnessing the ecological impacts of excessive atmospheric carbon and geological records tell us that our planet’s life forms will take a devastating hit.3  

Ecologically minded architects are attempting to reduce the carbon emitted by the building industry. Construction processes, product manufacturing and transportation, building operations, and demolition account for nearly 40 percent of the carbon dioxide released into the atmosphere by human activity.4 As building material specifiers, architects have an obligation to mitigate the environmental impacts of construction activities. This necessity will only increase as the structures we build over the next 40 years will double the world’s current building stock.5 

On the other side of the carbon equation is absorption and sequestration. One of the benefits of trees is that they pull carbon out of the air as they grow and, when used in construction, their wood keeps that carbon captured within (at least until the building is demolished). Other carbon absorption possibilities lie within our planted landscapes. The design of vegetation, landforms, and water features are opportunities for nature-based carbon absorption. How might designers facilitate this process?  

Landscape architect José Almiñana, principal of Andropogon, has been thinking about the relationship between carbon and the landscape for some time. His first answer to this question is Biodiversity. “We must avoid monoculture planting and design the most complex and diverse systems,” he explains. “The more complex the community, the greater the capacity to absorb carbon.” Hundreds of scientific studies confirm this idea: More diverse plant assemblages support higher biomass production and increased carbon sequestration.6  

As an example of a constructed, biodiverse landscape, Almiñana points to the Center for Sustainable Landscapes (CSL) on the campus of Phipps Conservatory and Botanical Gardens in Pittsburgh [site plan, below]. Andropogon worked with the conservatory to transform a steeply sloped brownfield that had suffered decades of environmental devastation into a sustainable landscape that captures and reuses all water on site. 

Phipps conducted multiple cross-discipline charrettes which included Andropogon, Design Alliance Architects, engineers, energy consultants, academics, and Phipps staff members. This collaboration facilitated the integration of landscape, building and infrastructural systems, including a large solar array, fourteen geothermal wells, underground reservoirs, and a wastewater treatment process consisting of settling tanks, constructed wetlands, sand, UV filters, and pumps that bring the water back up the hill for use in the restrooms.  

The planting plan includes over 150 varieties of trees and shrubs native to the Western Allegheny Plateau, all sourced from within 250 miles of the project. Designed communities of plants grow along the sloped site from the wildflower meadow on the roof to the lagoon below. As visitors descend through the changing topography, they experience the diverse plant systems of woodlands, lowland slopes, and wetlands. 

According to Richard Piacentini, president of Phipps Conservatory, “CSL serves to increase awareness of the interconnection between people, nature, and the built environment, and to promote sustainable systems thinking… Visitors can learn about the beauty and benefits of native plant communities, green infrastructure and its role in improving local water quality, while also seeing the wildlife, both terrestrial and aquatic.7” 

The varied landscape serves as a habitat for a vast range of butterflies and moths, and the  
lagoon is home to an aquatic ecosystem consisting of cattails, rushes, crayfish, perch, largemouth bass, and turtles. To diminish construction-related carbon emissions, landscaping materials were chosen for their reduced embodied carbon, including pavers cut from recycled concrete, locally sourced oak decking, and repurposed cobblestones.  

A decade after opening, the project has matured into a landscape that feels natural but is, in fact, a series of integrated ecological and constructed systems. CSL is a working environment that includes biodiverse habitats, a net-zero building, and serves as an active carbon sink. The success of the professional collaboration can be measured by the seamlessness of each discipline’s efforts. 

Connectivity is another concept relevant to the design of nature-based carbon absorption, according to Tavis Dockwiller, founder of Viridian Landscape Studio. Dockwiller objects to treating landscapes like “potted plants.” Vegetation needs to interconnect across a site and reach beyond its boundaries to compound the many benefits of plants, including carbon absorption. “Designers should focus on the big picture, rather than individual parts, and avoid fractured landscapes,” she says. “Our intent is to design working ecosystems which include the ground plane, shrub plane and tree canopy.” 

Viridian’s work at Fairleigh Dickinson University in Hackensack, N.J., is a case study in the benefits of designing with connectivity. The campus was built on drained wetlands and lies on two sides of the Hackensack River, which was degraded by decades of industrialization. University buildings were constructed without an apparent relationship to each other or their surroundings. The campus lacked a perceivable identity and any form of engagement with the environment. There was no sense of collective culture as few students were compelled to linger at the school. 

The University hired Viridian to help transform its metro campus into a sustainable and ecological landscape [site plan below]. Viridian’s master plan brought stewardship of the river into the university’s academic mission. Their design work began with a pollinator-attracting green roof and continued with a planting plan for the full campus. Native plants were utilized to increase natural beauty, create identity, affirm boundaries, and reduce maintenance. Soils, vegetation, and stormwater management were all designed in a coordinated manner. Over time, the multiple landscape projects successfully tied the campus together and contributed to the creation of what the school now considers an “eco-campus.”  

The largest and most impactful project at FDU is the Spirit Footbridge, which connects the two sides of campus across the river. The bridge utilizes tiered, hanging planters along its shifting sides to green its pathway. Native plants were selected for their suitability to the waterfront microclimate and their ability to contribute to the restoration of the riverine ecosystem by attracting insects and birds. They include creek sedge and other ground covers, colorful shrubs such as bush honeysuckle, and small trees.  

The bridge supports increased pedestrian activity and expands the riverfront ecosystem. Across the campus, native plants fill the spaces between the formerly disconnected buildings to establish a vibrant sense of place. People now engage with the campus and the river in new ways.  

“Viridian’s landscape is celebrated by students, faculty, and staff,” says Heidi Fichtenbaum, senior project manager for the university. “It knits the campus together in ways that encourage academic research and community engagement.” The vegetated connectivity promoted by the campus plan contributes to school-wide social interaction and increased carbon absorption. 

A third landscape concept described by both Almiñana and Dockwiller is the importance of planning for change over time. Ecoregional plant communities evolve and mature, and expectations at project delivery need to account for growth. It takes at least three years of dedicated maintenance for new landscapes to reach establishment and budgeting is necessary to support this effort. Additionally, designers need to plan for disassembly to allow future maintenance and modifications without generating the heavy emissions required by demolition and reconstruction.  

Rob Kuper, professor of landscape architecture at Tyler School of Art and Architecture, agrees with the principles demonstrated by these case studies but offers a less sanguine view on the carbon absorption potentials of new landscapes: “We can’t plant our way out of the environmental crisis. Plants simply cannot sequester carbon at a sufficient rate to counter our emissions,” he explains. 

Instead, Kuper focuses his attention on the emissions side of landscape construction. Diesel powered earthwork is a huge generator of CO2. If a new landscape project takes a hundred years to absorb the emissions required to build it, then the project is contributing to the problem, not solving it. He also studies the embodied carbon in landscape materials: “We should use less concrete, which has an enormous carbon footprint, and use more natural materials such as wood, stone and earth.”  

Air travel is a serious concern for Kuper. If a landscape architect takes a round-trip flight between Philadelphia and Los Angeles to visit a project site, they are responsible for the emission of nearly 3,000 pounds of carbon.8 In comparison, a sugar maple can sequester about 53 pounds of carbon per year. It would require the absorption efforts of 56 newly planted, 3-inch caliper maple trees to offset one trip to the west coast (disregarding the emissions required to bring the trees from the nursery). How can a design process be considered sustainable if carbon offsets are required before construction even begins? 

“The most important thing we can do to help with absorption rates,” says Kuper, “is to stop deforestation and allow secondary forests to expand.” Generally, we need to build less and reuse more, which in landscape architecture, translates into ecosystem restoration. In architecture, it underscores the importance of historic preservation and adaptive reuse.  

The logic of the carbon cycle tells us that in most cases, it is better to restore landscapes and buildings than to demolish them. When an existing building is re-used, a replacement building is not built, and the associated carbon emissions are not released. Additionally, the carbon sequestered in existing building materials remains in place rather than being emitted into the atmosphere through combustion or decomposition.  

Too often, new buildings are designed without sufficient regard for their surroundings, and landscape design is left as a disconnected afterthought. The projects at Phipps and FDU demonstrate a different paradigm — one that prioritizes integration of structures and landscape. Design concepts such as habitat connectivity and biodiversity expansion are embodied within these verdant landscapes, contributing to natural beauty, serving social needs, and absorbing atmospheric carbon. 

We have arrived at the current climate crisis by disregarding the consequences of our actions. Our patterns of settlement, manners of occupation, and methods of design and construction all require reevaluation and transformation to avert the worst consequences of climate change. As the built environment inevitably expands, building professionals must amplify the societal and climatic benefits of their efforts with multidisciplinary collaboration that addresses both the emissions and absorption sides of the carbon cycle. 

Tim Kerner, AIA is principal of Terra Studio, adjunct professor of architecture at Temple University, and co-chair of the Context Editorial Board.  

CITATIONS 

1. Holli Riebeek, “The Carbon Cycle,” NASA Earth Observatory, (2011) https://earthobservatory.nasa.gov/features/CarbonCycle 

2. Vaclav Smil, “Beyond Magical Thinking: Time to Get Real on Climate Change,” Yale Environment 360, (2022). https://e360.yale.edu/features/beyond-magical-thinking-time-to-get-real-about-climate-change 

3. Caroline Lear, et al. “Geological Society of London Scientific Statement: What the Geological Record Tells Us About Our Present and Future Climate.” Journal of the Geological Society, (2021) https://www.lyellcollection.org/doi/full/10.1144/jgs2020-239#:~:text=The%20geological%20record%20shows%20changes,concentrations%20of%20atmospheric%20CO2. 

4. Mathew Adams, et al. World Green Building Council, “Bringing Embodied Carbon Upfront.” (2019). https://worldgbc.org/advancing-net-zero/embodied-carbon/ 

5. AIA Blueprint for Better, “Architecture’s Carbon Problem,” https://blueprintforbetter.org/articles/architectures-carbon-problem/ 

6. Isabell Weiskopf, et al. “Biodiversity Loss Reduces Global Terrestrial Carbon Storage.” Nature Communications 15, (2024). https://doi.org/10.1038/s41467-024-47872-7 

7. Richard V. Piacentini, “Center for Sustainable Landscape Achieves Leed Platinum,” The Field, (2019) https://thefield.asla.org/2019/04/30/center-for-sustainable-landscapes-sites- 
platinum-certification/ 

8. https://co2.myclimate.org/en/flight_calculators/new 

PHOTOS:

CARBON EXCHANGE View from the roof of CSL with carbon absorbers in the foreground and carbon emitters in the background  

Photo: Paul G. Wiegman 

SITE PLAN Phipps Conservatory and the Center for Sustainable Landscapes in Pittsburgh  

Diagram: courtesy of Andropogon 

TIERED ECOSYSTEMS A descending landscape of biodiversity at Phipps Conservatory 

Photo: Paul G. Wiegman 

SITE PLAN Fairleigh Dickinson University in Hackensack 

Diagram: Viridian Landscape Studio 

NATURAL BRIDGE A new span at Fairleigh Dickinson University encourages pedestrian activity and connects the community to the river  

Photo: Sahar Coston-Hardy 

GREEN CONNECTORS Innovative landscape design creates an interconnected ecocampus 

Photo: Viridian Landscape Studio