As just one of their critical ecosystem services, trees play a crucial role in sequestering carbon dioxide (CO2) from the atmosphere. Through photosynthesis, trees absorb CO2 and produce oxygen and energy in the form of sugar (glucose). The carbon from CO2 is stored in various parts of the tree, including the trunk, branches, leaves, and roots—this is referred to as biogenic carbon.
Carbon sequestration by trees helps to mitigate atmospheric carbon dioxide, a greenhouse gas (GHG). Forests and other tree-rich ecosystems serve as "carbon sinks" by absorbing more carbon than they release, which could potentially help offset the carbon emissions from human activities such as using fossil fuel-based energy resources for building construction and operation.
Not all trees sequester carbon at the same rate
It is important to note that trees will vary in their ability to sequester carbon based on factors including the tree species, age, size, health, and the overall condition of the ecosystem.
Armed with knowledge about the degree to which certain species of trees can absorb carbon compared to other, building and site design teams may leverage such information to develop site designs that are optimized for carbon sequestration while still being appropriate and suitable species for their location. Moreover, project teams should be mindful of the rate at which various species of trees sequester carbon over their lifetime compared to the years after initial establishment (see figure below).
Figure: The initial annual carbon sequestration potential of ten tree species (planted at 2-inch caliper) compared to their potential over sixty years. Figure by Daniel Overbey.
Carbon sequestration adds up
There are a variety of tools and resources available to help building and site project teams calculate the carbon sequestration potential of trees. Once assessed, the carbon sequestration potential of trees can be leveraged to offset some degree of the embodied carbon of the site's hardscape and/or on-site building structures. The American Institute of Landscape Architects (ASLA) is championing the carbon sequestering potential of trees as part of their Climate Action Plan as on-site vegetation may play a significant role in low- and no-carbon building and site solutions.