Carbon Postitive Landscape

Landscape architecture strategies can play a key role in helping projects reach their carbon goals.

On the edges of the park surrounding the new multigenerational recreation center in development in Tracy, California, clusters of trees and plants will serve as “carbon gardens.” The carefully designed habitat will sequester an estimated 54.8 tons of CO2 annually, in addition to providing quiet zones and walking trails within the park.

“It’s the density and varied palette of tree types, shrub layers and ground cover planting that will work together to sequester the most carbon,” says Rocio Gertler, LPA Design Director of Landscape Architecture.

Feature Carbon Positive Landscape Cityof Tracy

As LPA’s integrated teams work toward zero-carbon projects, landscape architects are a vital part of the design equation. What’s around the buildings can play a restorative role, creating healthier environments that are a positive, proactive element in removing carbon emissions from projects.

“We’re in a unique position to actually reverse some of the impacts of the built environment,” LPA landscape architect Andrew Wickham says.

Working in an integrated design process, the landscape team can incorporate carbon strategies into the project’s core design and budget. A carbon-neutral landscape can add value by creating healthier spaces that attract tenants and address larger sustainability targets.

“As a multidisciplinary firm, we’re trying to think of ways to move beyond simply doing what’s required by the state or by the county,” says LPA Director of Landscape Architecture Rich Bienvenu. “Designing within the natural environment, we need to overlay the science and collaborate with ecologists who can help inform our design decisions.”

As landscape architects analyze projects, several strategies are available to help clients get more from their investment.

Feature Carbon Positive Landscape Photo 1
All plants help in carbon sequestration. Larger shrubs are particularly great at it, and can help create privacy or screen unwanted views.

Choose Sequestering Plants

Plants do the work of consuming carbon. Recent research has helped identify the best carbon-hungry species. In commercial landscapes, large deciduous tree like maples, oaks andLondon plane trees are all good choices for a carbon-sequestering garden.

Water requirements, maintenance and local regulations all play roles in the plant choice, but carbon-sequestration capabilities can help tip the scales. And the results are measurable. In the new West Hollywood Aquatic and Recreation Center, 96 trees newly planted in the park will sequester approximately 21,453 pounds per year or 858,104 pounds of carbon over a 40-year period.

Use Native Plants

A common-sense approach that hasn’t always been routine practice is to grow plants native to an area. They don’t require much additional water or fertilizer to flourish, and maintenance will be kept to a minimum — all carbon-positive results. “We try to use native plants where appropriate as much as possible because they’re already adapted to the climate and support local insects and animals,” Wickham says.

Feature Carbon Positive Landscape Stomwater Mgmt Ecosystem Service
The planting at Tracy’s El Pescadero Park and Multigenerational Recreation Facility is designed to look beautiful while also providing a multitude of benefits, such as slowing down, capturing and cleaning stormwater runoff, supporting healthy wildlife and sequestering carbon.

Tiny Forests

Research illustrates the value of a larger mélange of planting; a handful of sculptural plants on lawns is a condition that exists almost nowhere in nature. Diverse landscapes resembling those that develop naturally are far healthier, and they can be used as screens or quiet areas.

LPA has drawn increasingly on Japanese botanist Akira Miyawaki’s work on “tiny forests,” dense planting schemes in which plants can grow up to 10 times faster than when spread out. The carbon sequestration and air quality benefits are dramatically higher than more-dispersed schemes. “When you combine carbon-thirsty plant species in a slightly denser planting style, the sum will sequester three or more times more carbon than a traditional landscape,” Wickham says.

Rewilding

Restoring the innate and self-sustaining character of nature helps develop a diversity of carbon-active plant life. “Rewilding” is unpredictable, but a variety of naturally growing species improves the chances of plants succeeding, and growing and shedding organic matter throughout the year, resulting in carbon sequestration and improved soil health, which can contribute to soil’s ability to absorb and hold more carbon.

Preservation

Preserving natural features on site is often the most sensible and cost-effective carbon-mitigation strategy. An existing tree is often better than a replacement, which may take decades to grow. It also doesn’t cost anything and will be easier to maintain. Early engagement allows landscape architects to identify these opportunities in the initial planning process, another benefit of the integrated design process.

Feature Carbon Positive Landscape El Pescadero Park
The landscape design for El Pescadero Park in Tracy, California, uses layers of trees, shrubs and ground cover in varying densities to sequester carbon.

Avoid Expanding Lawns

Turf grass and lawns are best used when they serve specific functions, not simply serving as green carpet. Programming needs should drive design decisions, but the design process can search for alternative solutions that may achieve many of the site goals.

“For example, establishing meadows or planting species that are less maintenance-intensive and not requiring the application of a bunch of chemicals would be far more beneficial,” Bienvenu says.

Paving Diets

Reducing paved areas can dramatically reduce the carbon impact of outdoor spaces. Circulation patterns should be carefully analyzed to determine the number of people that will use the path and the necessary width. The ability to reduce the width from 10 feet to 8 feet can make a difference in cost and carbon.

When incorporating hardscapes, it’s helpful to shade them as much as possible or use high-albedo materials to increase solar reflectivity and reduce the heat island effect.

Feature Carbon Positive Landscape Cityof Tracy Resiliency Ecology
To create a variety of experiences and assist with way-finding, El Pescadero Park was organized into a series of “rooms,” each with a unique planting style and character. Bold colors and forms in the planting help announce arrival and entry, while native meadows create a natural-feeling escape from the city.

Material Choices

The nature of paving or hardscape utilized is also centrally important. Decomposed granite, gravel or mulch are considerably more environmentally friendly than concrete.In some cases, paths can consist of multiple layers, with porous outer layers lining concrete central paths.

The sourcing of materials, including furnishings and other elements, also should be part of the evaluation of carbon costs. “Understanding local material availability when designing is key,” Gertler says. “There is no need of bringing materials produced far away, as transporting materials causes a lot of carbon emissions.”

Knock-on Effects

A carbon-positive approach can produce benefits beyond sustainability. Plantings that don’t require irrigation save resources and infrastructure. Stormwater retention, an essential part of any design, can be entwined with larger design elements. For Palomar College in San Diego County, the water treatment system was expanded to include an amphitheater that plays multiple roles on campus and puts people at the center of the sustainable feature.

For schools and civic projects, the carbon strategy can serve as a teaching opportunity, educating the community about the function and impact of the choices made in the design process. Signage and respite spots help engage and connect people with the project and its sustainable goals.

We’re in a unique position to actually reverse some of the impacts of the built environment.” — Andrew Wickham, PLA, LPA Landscape Architect

Feature Carbon Positive Landscape Photo 2
Landscapes are more than just aesthetics–they reduce water use, mitigate localized flooding and restore ecosystems.

Producing Results

Every project deserves a close examination of the ability of landscape to reduce the carbon footprint. Most landscape strategies are going to be more successful when integrated into the larger design process.

“I don’t think most of that would be possible if we were all operating in silos,” Wickham says. “It’s hard to produce results when the architect just brings the schematic design to a landscape architect and says, ‘shrub it up.’”

Landscape, more than most disciplines, requires a long-term approach. The design will shift and evolve as plants grow and nature has its effect.

“It’s not like a building where once it’s built, you’re done,” Gertler says. “Landscape is something that’s just starting when you’ve finished.”


Sidebar: Measuring Carbon in Landscapes

The Climate Positive Design Pathfinder tool is one of the useful tools available to help designers measure carbon in the exterior built environment. A range of project elements are entered into the app, which calculates the number of years until the landscape will begin to sequester more carbon than is embodied in that project’s construction.

Feature Carbon Positive Landscape Sidebar 1

For example, for the design of Britton Middle School, under construction in Morgan Hill, California, a shift to low-carbon materials changed the building’s timeline to carbon neutrality from 40 years to 24 years.

“Perfection is often difficult, but improvement usually isn’t,” says LPA’s Andrew Wickham.

Feature Carbon Positive Landscape Sidebar 2