Among their many ecosystem services, it is common knowledge that tress are essential to for the air we breath. (I could not help but reminisce of this classic Arbor Day Foundation PSA from my youth.)
Trees sequester stormwater, purify air, reduce the urban heat island effect, promote biodiversity, and offer physiological benefits to people. All of these benefits come with direct and indirect economic benefits.
Trees are also a tremendous carbon sink and may contribute significantly to reducing the lifecycle carbon intensity of any site development. Better yet, we have the tools to quantify the carbon sequestration potential of trees.
i-Tree Planting Calculator
Among several other calculators and methodologies to assess the carbon sequestration of trees, i-Tree is a free, state-of-the-art, peer-reviewed software suite from the USDA Forest Service that provides a variety of urban and rural forestry analysis and benefits assessment tools. By specifying the number of trees, tree species, size of trees at planting, condition of the trees, and number of years in the project's lifetime, the i-Tree Planting Calculator will assess the potential cumulative lifecycle carbon dioxide sequestered.
A Case Study
Quantifying the carbon dioxide sequestered by trees within a site development may serve a project team's embodied carbon intensity figures by offsetting the emission expended to physically construct the built components. Consider the example below. This site development will establish over 200 new trees, which are anticipated to sequester 1,651,548 pounds (749,130 kilograms) of carbon dioxide over the 60-year lifecycle of the development's 53,400 square foot (4,961 square meters) office building. The embodied carbon intensity of the building's structure and enclosure is anticipated to be approximately 1,100 lbs CO2e/ft2 (about 500 kg CO2e/m2).
If we divide the carbon sequestration of the project's trees by the area of the building, we will see that the trees may sequester over 30 lbs CO2/ft2 (151 kg CO/m2) - which is about 30 percent of the embodied carbon intensity of the building. To be fair, if we start looking beyond the building footprint, then we need to incorporate the embodied carbon from the site hardscape as well. Nevertheless, the order of magnitude of the carbon sequestration of tress is considerable.
Figure: Site plan highlighting the trees accounted for regarding on-site carbon dioxide sequestration. The i-Tree Planting Calculator can be used to quantify the potential cumulative lifecycle carbon dioxide sequestered by the various trees and shrubs on a project site. Browning Day recently applied this tool on an office building development in Fort Wayne, Ind., in pursuit of a LEED v4.1 pilot credit. Source: Browning Day. Special thanks to Brett Schlachter and Alireza Shayesteh for helping produce the figures for this project example.
Table: Cumulative carbon dioxide sequestered by on-site trees. The i-Tree Planting Calculator can be used to quantify the potential cumulative lifecycle carbon dioxide sequestered by the various trees and shrubs on a project site. Browning Day recently applied this tool on an office building and site development in Fort Wayne, Indiana, in pursuit of a LEED v4.1 pilot credit. Source: Browning Day. Special thanks to Brett Schlachter and Alireza Shayesteh for helping produce the figures for this project example.
There is a LEED Pilot Credit for This
The LEED v4.1 pilot credit SSpc158: Onsite Carbon Sequestration Through Plantings aims to increase the awareness and understanding of a site’s carbon impact by prompting teams to assess and increase the carbon sequestration capacity of trees and shrubs onsite.
The pilot credit calls for using the i-Tree Planting Calculator to assess the amount of CO2 sequestered by all trees and shrubs on the baseline site compared to the proposed site.
After completing the assessment, the pilot credit requires the team to compare the proposed site’s sequestered carbon to the baseline condition to demonstrate a minimum 10 percent improvement in carbon sequestered. (USGBC is open to alternative strategies to help achieve the intent of this pilot credit).
Quantifying the Impact of Trees at the City Scale
The carbon sequestration potential of trees and other vegetation has implications regarding municipal greenhouse gas reductions efforts as well.
Consider the New York City Street Tree Map. Developed by the New York City Department of Parks & Recreation with the help of various strategic partners, over 690,000 trees have been identified and mapped through an online public visualization tool. In aggregate, the trees mapped by NYC Parks may sequester nearly 1.2 billion tons of carbon dioxide every year. To put this figure into perspective, it equates to the greenhouse gas emissions of over 230 million gasoline-powered passenger vehicles being driven for a year.
As site development teams and municipalities pursue aggressive greenhouse gas reduction targets, the carbon sequestration of trees and other vegetation can and should be a critical component of any comprehensive strategy.
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