Plants and living landscapes are a crucial part of carbon draw-down solutions for overall climate positive design.  Soil is one of the largest carbon sinks in the world, storing more than the atmosphere and living plants combined. Plants can store carbon in their above ground and root biomass for hundreds of years in large mature trees, growing forests, and grasslands. Using plants and managing healthy soil to draw down carbon while being considerate of not disturbing soil when possible is a huge benefit that landscape architects will make toward positive climate change solutions in landscape projects.

Oregon’s Climate Action Plan calls for increasing natural sinks within the State’s natural and working lands. In 2021, the commission adopted a Natural and Working Lands Proposal that set goals for carbon capture and storage on Oregon's natural and working lands. Read the 2023 Report that addresses opportunities for carbon sequestration measures within different landscape types.

Carbon Drawdown with Soil

Soil is the largest carbon sink on land because it contains billions of living fauna, bacteria, and fungi interacting with plants and minerals belowground. A teaspoon of soil contains 10,000-50,000 different species of organisms and miles of fungal filaments. These living microorganisms use carbon from the atmosphere to create microbial biomass.  When the soil is undisturbed that biomass is sequestered indefinitely in the soil.

Carbon Drawdown with Plant Biomass

Plant biomass is a more commonly known part of the carbon cycle.  Plants draw CO2 from the atmosphere and also use that carbon for their plant biomass, their leaves, woody structures, and roots.  When designing vegetation on landscape projects, create large dense planting beds with the criteria of carbon sequestration potential in mind.

Biomass

Choose slow to medium growing, long lived trees, and use ‘right plant right place’ principles to locate trees where they can grow to their fullest maturity.  Long lived trees with dense wood store the most carbon for hundreds of years. Rice University created a list of 17 ‘Super Trees’ local to Houston to sequester carbon. Common urban trees and PNW natives could be use for a Oregon list of ‘Super Trees’ (see Super trees’ may help save Houston … and beyond).

Root Systems

Choose perennials, grasses and, where possible, trees with deep, extensive root systems, such as our PNW native bunchgrasses, that store high amounts of carbon within their filament root biomass and contribute to a healthy microbial community.  Grasslands are becoming an increasingly important carbon sink as more forests are being developed and are now prone to large wildfires (see In Wildfire-Prone California, Grasslands a Less Vulnerable Carbon Offset Than Forests).

Forestry Practice

Increasing the length of time between harvest can significantly increase both profit and carbon sequestration within PNW forests.  (Read Yes, Long Rotations Can Yield Real Climate Gains for Cascadia )

Carbon Drawdown with Installation and Management

Avoid Soil Disturbance

• The key to storing carbon draw-down in the soil is managing landscapes to produce a healthy ecosystem for plants and their relative microorganisms, and not disturbing the soil, which releases carbon back into the atmosphere.

• At the planning stage, locate where large mature trees and soil can be left undisturbed, and if disturbance must occur where possible only disturb it once, then plant densely.

Organic Amendments

• Amending soil with compost and biochar activates the microbial productivity and relationships with newly established plants, which will jump start the carbon storage productivity in the soil and through healthy plant biomass. 

• Using organic amendments such as compost and biochar is more successful at carbon sequestration than chemical fertilizers. For more information see Soil and Biochar.

Responsible Sourcing

• Use recycled compost from yard debris over engineered or excavated soils such as peatmoss. Check our Sunderland Yard to purchase compost and gravel.

Use On-Site Carbon

• Amend soils with organic matter and create a healthy microbial ecosystem, use the existing plant biomass as a long term landscape management strategy.  The carbon captured with your landscape projects trees, shrubs, and perennials can be left on site and sequester carbon by slowly decaying into organic matter while feeding the microbial networks the soil. 

• Recent studies show that in places where people have left their leaves to decompose, the soil holds up to 32% more carbon on average.  If you are worried the leaves will not decompose quickly enough, ask your landscape contractor if they will provide leaf shredding and application to replace yearly mulch application. 

• Large, hard to burn woody pieces such as logs and branches should be considerate for fire-wise landscapes. Learn more in Fire in the Landscape.