By Rachel Lindsay, Head of Site Design + Worker-Owner, Regenerative Design Group
Ecological landscape design has always recognized soil as a valuable natural resource to be conserved and protected. And yet, as a conscientious landscape designer, lifelong avid gardener, and former farmworker, it has been humbling to realize the full—mostly invisible—impact that working the soil has, despite my best intentions.
Every shovelful of soil lifted up and turned over mixes up a finely tuned structural system of micro-organisms and nutrients, and introduces oxygen into the lower layers, initiating or speeding up the decomposition of Soil Organic Carbon (SOC) and releasing carbon dioxide into the atmosphere. While soil is relatively malleable, and so easily moved and sculpted compared to other landscape elements, the life and chemical composition of healthy soil can take decades to centuries to return to its pre-disturbance state. After a few seasons, seed and transplants are established and the disturbance may be no longer obvious, but underneath the surface the soil takes a lot longer to heal.
Two 2.5-acre sites: Site A showing business as usual, Site B showing ‘Soil-smart’ practices. Looking solely at soil disturbance and the designed revegetation, Site A has a 30-year carbon loss of 290 metric tons, or the emissions equivalent of 2.7 million driving miles. Site B has a 30 year carbon loss of 121 metric tons, or the emissions equivalent of 1.1 million driving miles. If no development had occurred on either site, these 2.5 acres would each have an estimated 30 year carbon gain of 56 metric tons, equivalent to the emissions offset of 500,000 miles. Source: RDG
Limiting soil disturbance to what is minimally necessary is an obvious first step in reducing the conversion of SOC into carbon dioxide, but some soil disturbance is necessary for the establishment of habitat (ours, primarily). As directors of that disturbance, landscape architects, designers, gardeners, and landscapers have a profound influence over soil health and the role it plays in the global carbon cycle. Soil science research shows us many ways that soil management and specification during a landscape design and installation can help create optimal conditions for soils to return to their maximum health and carbon storage capacity after the physical work is completed.
Soil is one of the earth’s largest carbon reservoirs, and soil disturbance is a major contributor to greenhouse gas emissions all over the world. And yet, no other element of the built environment has the potential to provide ongoing carbon sequestration after the completion of an installation. Including healthy soil management practices as part of the overall effort to decarbonize the building sector could prevent unnecessary carbon from being released into the atmosphere and increase long-term carbon sequestration and storage capacity in existing and new construction. Limiting soil disturbance and maximizing SOC sequestration potential is the only way a development site can truly become carbon neutral or a carbon sink. The protection and restoration of healthy, high-functioning soils onsite is an underutilized approach for developers who want to reduce the carbon footprint of the building sector and bring greater coherence to our ability to live and thrive in both urban and rural environments.
Carbon Accounting in the Landscape
In many environmental monitoring and evaluation applications, ‘carbon footprint’ has become synonymous with ‘environmental impact’. In Regenerative Design Group’s research for the Massachusetts Healthy Soils Action Plan (authorized by the Baker administration in February 2023), we found this to be also true for soil: soils with higher levels of Soil Organic Carbon (SOC) offer greater environmental services all around. They have higher fertility and support healthier plants. Higher levels of SOC improve soil water-holding capacity and filtration, reduce vulnerability to erosion, and mitigate climate change by binding carbon into the soil for long-term storage. In short, if we set ourselves the goal of increasing the amount of SOC in the soils we work with, we can accomplish a broad range of ecological goals along the way.
Carbon accounting in the built environment was spearheaded by architects and is rapidly becoming integrated into standard landscape design evaluation and criteria. Yet, soil remains missing from almost all Life Cycle Assessment tools and incentives, despite the available data on the role of soil in the carbon cycle. Pathfinder and Carbon Conscience are two online tools for landscape architects, designers, and planners that integrate the embodied carbon of both landscape material manufacturing and transportation with an estimate of the carbon impact of the designed landscape (and site disturbance).
These tools are only able to approximate the impact that planting or disturbing a particular soil might have, but they are extremely valuable in helping to quantify the invisible impact that different approaches to a project might have. They also help us internalize soil health and management into our workflow. Soil assessment and management, through all stages of construction and maintenance, needs to take center stage for our work to result in healthy, climate-resilient, biodiverse landscapes.
The soils and landcovers on every site are unique. Soil texture, parent material, climate, historical land use, and vegetation greatly impact aspects of soil formation, nutrient availability, and biological activity. Soil health is determined by a soil’s capacity to operate as a dynamic, living system that maintains essential environmental and ecological functions. For this reason, a ‘healthy’ soil found in one geographic area can be composed of completely different “ingredients” than a ‘healthy soil’ found in another area. No single tool or app is going to be able to take the unique qualities of a site and spit out a perfect recipe for soil restoration.
Putting Soil to Work
Protecting and promoting healthy living soil systems is what unlocks the massive carbon storage potential of soil; the digestive processes of microorganisms and roots transform carbon dioxide into Soil Organic Carbon. Soil that is stripped, compacted, and chemically dependent cannot support a healthy microbiome. Without soil organisms, plants are unable to obtain the nutrients they need to thrive; they become nutritionally deficient, more susceptible to pathogens, and more reliant on chemical pesticides and fertilizers. These vulnerabilities can negatively affect the health of humans and ecosystems, as well as create a time and resource sink for landscape management. Water becomes a problem to be ‘managed’ rather than a resource, and increasingly destructive natural forces more easily damage costly landscapes.
The design and management decisions we make when building directly impact the health and vitality of the soil. When we better understand soil, we can use the construction process to intervene and produce the best possible soil function outcomes for stormwater management, climate resilience, wetland protection, and carbon capture. When soil is protected, rehabilitated, and managed with practices that support healthy soil biology, it results in greater productivity, carbon sequestration, and resilience to ecological disturbance.
What Builds Soil Health?
- Limited Disturbance
- Permanent Vegetative Cover
- Diverse Soil Food Web
- Remineralization + Nutrient Management
- Protection from Compaction, Contamination, + Conversion
The living biology in the soil—the soil microbiome—makes nutrients available for plants, holds moisture, and creates a system able to effectively build and store carbon. See infographic here for more.
Best Management Practices
The growth trends in the Massachusetts Healthy Soils Action Plan (HSAP) predict that over 360,000 additional acres of soil in Massachusetts may be impacted by development over the next 35 years. That means 360,000 acres of soil will likely have some portion of stored carbon released back into the atmosphere. The difference we can make in how this development is conducted is significant. Shifts in design and management practices, such as planting 25% of existing open lawn with trees,and increasing our soil specifications and management to reach a minimum of 3% organic matter in the top 8” of lawns, could sequester an additional ~180,000 tons of carbon dioxide equivalent per year—comparable to the electricity consumption of over 37,000 average U.S. homes for one year.
Last year we brought a group of design, planning, and construction professionals together to compile the Healthy Soils Guide for Site Design + Construction. We hope that this collection of best management practices helps everyone involved in a project work together to maximize the carbon sequestration and storage potential of soils in development projects. Whether these are in highly impacted, urbanized areas or greenfield development, there are actions we can take to reduce the release of CO2, speed the return of carbon to the soil, and keep it there over the long term.
Through conversations with practitioners, contractors, and scientists, we developed a set of strategies to approach soil management on landscape and development projects. These strategies can also be considered as varying levels of intervention, from low cost/low intervention (protect) to high cost/high intervention (recreate). Whether a project is a large planning project that can incorporate metrics and carbon accounting protocols or a small DIY renovation in your own backyard, applying these strategies to the process will result in lower carbon dioxide emissions and restore healthier soils more quickly:
- Protect sensitive and valuable areas from impact
- Rehabilitate soils for better ecological function
- Relocate soils that will be disturbed by construction using best management practices
- Recreate soils using offsite mixes and amendments to add to, alter, or replace removed or compromised soils.
While these may seem straightforward, there are a myriad of ways that these may play out within a project. For example, protecting an area might be accomplished by reducing the size or weight of the machinery allowed on site, installing 9” of woodchips wherever vehicles will need access, or using physical barriers like boulders to constrain an area of disturbance. Compost is generally the go-to amendment for soil rehabilitation, but a nitrogen-fixing cover crop might be a better choice in some situations. Whether your role is contracting, installing, or maintaining landscapes, applying these strategies can help reduce the unnecessary loss of valuable Soil Organic Carbon, and improve the health of the soils we impact.
Applying Best Management Practices for healthy soils at a new build included limiting the zone of disturbance as tightly as possible, preserving mature trees as close as 13 feet from the foundation.
See www.masshealthysoils.org to access online and PDF versions of the Healthy Soils Guides, a library of Healthy Soil Resources, and submit comments or feedback for future revisions.
As Head of Site Design at Regenerative Design Group, Rachel Lindsay works principally with organizations and homeowners to create productive, resilient landscapes. She draws from her experiences in organic farming, Latin-American sustainable development, and art to facilitate a design process that prioritizes cultural sensitivity and environmental integrity. Rachel approaches projects of all scales through a soil, carbon, and water conservation lens, working to reduce the environmental impact of design installation while meeting client’s goals and aesthetic preferences. A worker owner at RDG, Rachel was a member of the steering committee that led the ownership transition process and has been the Treasurer of the Board of Directors since its establishment in 2022. Rachel holds an MS in Ecological Design from The Conway School, a BA in Anthropology from Wesleyan University, and is a certified Pollinator Steward with the Pollinator Partnership. When she isn’t working, she may be found in her garden, cooking with the latest harvest, or outside with her husband and young kids.