Assessing the Carbon Sequestration Potential of Roadsides and Roadside Revegetation

As described in the final report, the research team's estimate of roadside acreage available for CCS relied on the concept of the “road effect zone” (REZ), an area defined as 50 m from unpaved roads and 100 m from paved roads. Based on this definition, the team estimated that there are over 17 million acres within the REZ that are available for CCS. To estimate the potential carbon uptake within this area, the team relied on measurements of net carbon dioxide (CO2) exchange from a large sample of globally distributed eddy covariance towers arrayed according to functional vegetation types. Then, for each of four FLMA case studies across four distinct biomes, team members calculated the distribution of functional vegetation types within the REZ and estimated the total annual carbon flux. They then extrapolated these estimates nationally based on the total REZ area available for CCS. The team estimated that the eight FLMAs have the potential to collectively capture and store nearly 8 million metric tons of carbon each year. In reality, current carbon uptake is likely constrained within the REZ due to factors such as soil compaction, soil-nutrient limitations and pollution. The estimates of CCS, therefore, are intended to demonstrate the potential for carbon uptake given the prospects of future enhanced roadside vegetation and soil management.

The objective of this project is to develop a method to determine the carbon sequestration potential of roadsides and roadside revegetation. WTI estimated the amount of acreage available and the amount of carbon sequestration captured and stored along eight federal land management agencies’ roads.

Climate change has been attributed to increased concentration of carbon dioxide (CO2) in the atmosphere. The primary methods to reduce atmospheric CO2 are through the reduction of emissions, the capture and storage of CO2 to prevent its release into the atmosphere, and the absorption of atmospheric CO2 by vegetation and soil. Growing native revegetation along the roadsides and using vegetation disturbed during the construction of the road may present an opportunity to increase the absorption of CO2 through transportation projects. A variety of forest and agricultural practices have proven effective at increasing carbon sequestration (e.g., reforestation, no till cropping, changing grazing practices). However, the amount of carbon storage by vegetation and soils in U.S. highway right-of-ways (ROWs) is unknown, and the potential for increasing carbon storage in ROW vegetation and soils has not been articulated. Much of what is being learned in agriculture and forestry may be applicable to roadsides. Through this project, WTI will conduct a “carbon audit” for the Coordinated Technology Implementation Program (CTIP) of the Federal Lands Highway division of FHWA, which will include an evaluation of the carbon sequestration potential of roadsides and roadside revegetation, and identification of roadside management strategies that increase carbon storage or decrease CO2 emissions.