As the impacts of the climate crisis become more widespread, landscape architects are increasingly planning and designing landscapes with carbon in mind. At the ASLA 2021 Conference on Landscape Architecture in Nashville, landscape architects offered new approaches and tools for sequestering both operational and embodied greenhouse emissions in their projects and reaching a climate positive state faster.
According to Pamela Conrad, ASLA, founder of Climate Positive Design and principal at CMG Landscape Architecture in San Francisco, approximately 75 percent of all emissions are from the urban built environment, with 40 percent from buildings and 35 percent from transportation and landscapes.
To encourage landscape architects to sequester more carbon than they emit through their projects, Conrad founded Climate Positive Design two years ago. The original goal of the effort was to achieve one gigaton of carbon sequestration across all landscape architecture projects by 2050; now that goal has moved up to 2040.
“We need to keep warming to 1.5°C. We can only add 300 gigatons of additional carbon to the atmosphere and need to work within this remaining carbon budget. We need to reduce emissions by 65 percent by 2030 and hit zero by 2040.”
Over the past year, Conrad, along with ASLA, the International Federation of Landscape Architects (IFLA), and Architecture 2030 have encouraged design professionals and global policymakers to strive to achieve these targets. Conrad and ASLA partnered with IFLA to develop a Climate Action Commitment, which represents the voice of 70,000 landscape architecture professionals worldwide across 77 national member organizations of IFLA. All organizations also signed on to Architecture 2030’s 1.5°C COP26 Communiqué, which has the backing of more than one million planning and design professionals worldwide. “This represents a collective commitment,” Conrad said.
The importance of ramping up nature-based carbon sequestration is abundantly clear, but there hasn’t been enough progress. Today, “landscape architects are likely emitting more greenhouse gas emissions than they are sequestering,” Conrad said. “It’s time for radical change in the field of landscape architecture.”
Since its founding, the data in Climate Positive Design’s Pathfinder app has only improved. Thousands of projects have been logged in 85 percent of countries. The tool has helped landscape architects find ways to reduce space for carbon-intensive hardscapes and increase carbon-sequestering trees, shrubs, and grasses. This is critical because the data shows that 75 percent of carbon in landscape projects is embodied in materials like concrete and metal furnishings, while 25 percent is driven by operations, caused by fossil fuel-powered lawn movers and leaf blowers, and fossil fuel-based fertilizers.
According to her calculations, when completed, the projects already logged will result in 1.6 million new trees planted, which is equivalent to taking 800,000 cars off the road. “The tool has helped landscape architects increase planting by 18 percent.”
For Conrad, climate-smart design isn’t just about doing good for the planet; it’s also personal. Living in the San Francisco Bay Area, she has also experienced the impacts of climate change, like many millions across the world. “I have experienced flooding, devastating fires to the point that I couldn’t go outside, power outages, and, eventually, displacement.”
Chris Ng-Hardy, ASLA, a senior associate landscape architect with Sasaki, a multidisciplinary planning, landscape architecture, and architecture firm, said the contemporary study of ecology and conservation often feels like “we are documenting the end of the world.” But landscape architecture offers a way to shift that mindset. “Design is an optimistic act; it’s productive.”
Sasaki often works at the urban scale, focusing on large and long-range planning projects. They found early site planning decisions can dramatically impact future carbon emissions. “We realized we need to consider carbon from the beginning, before the project even starts.”
Ng-Hardy expects that in the near future developers will increasingly use the landscape portion of large urban projects to offset carbon from the development of buildings and infrastructure.
But in order to accomplish this, developers and designers need solid data on both embodied and operational emissions to guide early planning, and, unfortunately, there are major gaps. “Measuring embodied carbon is about 10-15 years behind the curve in terms of measuring operational carbon.”
To tackle these obstacles, a team at Sasaki used a year-long internal research grant to explore lifecycle assessments and environmental product declarations, developing the Carbon Conscience App in the process. The tool is meant to help with the preliminary planning decisions that determine a project’s long-range carbon footprint. “We are stepping up to help clients integrate this into their work.”
The assumptions underlying the carbon calculations in the tool were developed from a comprehensive academic and professional literature review covering buildings, infrastructure, and landscapes. Ng-Hardy said, for example, data shows that of dry biomass, “about half of the weight is carbon.” The tool could help policymakers get a sense of how much carbon is being sequestered naturally across the U.S.
The result of all of the research led to a few conclusions for landscape architects: “don’t destroy ecosystems; add wetlands, prairies, and forests; minimize hardscapes and concrete; and reduce the use of plastics and metals.” Ng-Hardy added that “not all metals are the same — recycled metals are better,” but it’s best to use wood materials wherever possible. And overall, “less is more — everything has impact.”
The conversation then turned to natural carbon sequestration in plants and soil communities. Deanna Lynn, Assoc. ASLA, landscape designer with Wild Land Workshop, a landscape architecture firm that focuses on “endemic landscapes for outdoor living, biodiversity, and water conservation,” said “soil carbon sequestration is hard to study.” But generally, the “more life there is in ecosystems, the more carbon is stored in soils.”
Beneath the surface, there is a complex web, made up of tree roots, organic matter, microbes, earthworms, mycorrhizal fungi, and insects. As described in the book The Hidden Life of Trees: What They Feel, How They Communicate―Discoveries from A Secret World by Peter Wohlleben, just one aspect of this underground world is incredibly fascinating: mycorrhizal fungi, which form a subterranean “world wood web,” enable trees to share carbon, nutrients, and information across their roots.
Soil ecology is complicated. For example, Lynn said “soil microbial communities are much more important than soil structures” in sequestering carbon. This speaks to the “chemical nature of the organic matter in soils.”
Soils are also “complex, adaptive systems.” When designing for carbon sequestration, it’s important to understand soils as “nested within larger and smaller systems” that change over time. The goal should be to support “self-organizing systems of soil life.”
She argued that when trying to understand the overall carbon sequestered in a landscape, it’s important not to just estimate the carbon in trees with a lot of biomass, like a sequoia, but to examine the whole tree, plant, and soil system. The diversity of plants, including their root range, type, and depth, are also meaningful.
Lynn has found that more carbon can be stored naturally in ecosystems and soils if species diversity is increased. Landscape architects can introduce more woody plants; warm season grasses; deciduous trees, which are denser; and nitrogen-fixing plants, which enable the productivity of the entire plant communities. Overall, native plants, which have deeper roots, are “more productive and resilient” and therefore will store more carbon over time.
In designing new forested landscapes, Lynn advised referring to a nearby ecosystem and mimicking their arrangements of trees and plants, along with planting an understory of plants that tolerate leaf litter. In all projects, leaf litter should be kept, along with tree logs, which help build carbon in the soil.
In the Q&A, the speakers noted that a “cultural shift” is needed to embrace the “messier” look of ecological design, which has greater carbon and biodiversity benefits. Ng-Hardy said that “the emissions from all the lawns in America are baffling. Lawns are the biggest cash crop in this country. But we need to encourage native plant gardens, a different aesthetic, as our new cultural norm and standard.” Then, landscape architects can increasingly reduce carbon and support biodiversity.