Date of Award
Master of Science (MS)
Plant and Soil Science
Roads alter the ecological landscape and affect the function and composition of nearby soil chemistry and plant communities in an area of impact termed the “edge-effect zone”. While the 6.3 million kilometers of roads in the US cover only about 1% of the land, the edge effect zone around these roads has been estimated to occupy nearly 20% of the total land area in the US (Forman 2000). The objective of this study was to examine the spatial extent of transported materials and impacts on forest soil and vegetative communities immediately surrounding roadways based on road types classified as “Highway,” “Two-Lane Paved,” and “Gravel.” This research was located within two watersheds in the state of Vermont, in areas where a substantial area of forest existed adjacent the roadway. Using GIS mapping, transects were constructed at right angles to the road, and samples were gathered at the Shoulder, Ditch, Backslope, 10m from the edge of the forest, and 50m from road center during the summer of May 2009 to August 2009. Soil samples were analyzed for a suite of nutrients and physical characteristics, as well as heavy metals. The forest composition and percent area coverage by species of herbaceous flora and woody shrubs were also recorded. The main effects from roads were dependent on the extent of clearing and topography modification required for a roadway. The spatial extent of these modifications was correlated positively with road use intensity. Highways have the greatest ecological impact and gravel roads the least impact. The cleared area defines how much sunlight is available to plant communities and the distance that road pollutants will travel. Some heavy metals (such as Pb, Cd, Ni and Zn) were correlated positively with road use intensity. Gravel roads have higher calcium content in nearby soil when compared to other road types. This is most likely due to mobilized dust from the road base. Proximity to all road types had neutralizing effects on the soil pH relative to the acidic native forest soil. Changes in microtopography next to the road have marked effects on the composition of plant communities through maintenance and direction of water flow. Ditch areas support wetland plants, and have greater soil moisture and sulfur content, while plant communities closer to the road are characteristic of drier upland zones. The area past the edge of the forest does not appear to be affected chemically or physically by any of the road types, possibly due to the dense vegetation that develops outside of the right-of-way. To reduce the ecological footprint of future road development, road corridors should be narrowed, traffic consolidated to mass transit systems such as busses or railroad, and buffer zones of vegetation next to the right-ofway should be encouraged to contain the spread of pollutants.
Asmussen, David, "The Spatial Effects of Road Use Intensity on Forest Plant Communities and Soil Chemistry" (2011). Graduate College Dissertations and Theses. 12.