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.

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Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management

Boreal mixedwood forest stands are comprised of a mixture of small canopy patches of varying dominance by conifer (mostly white spruce (Picea glauca (Moench) Voss)) and broadleaf (mostly trembling aspen (Populus tremuloides Michx.) trees. The purpose of this work was to extend our understanding of the patterns and causes of variation in understory vascular plant communities in unmanaged, mature boreal mixedwood forests. First, I assessed variation in understory community composition in relation to canopy patch type (conifer, mixed conifer-broadleaf, broadleaf, gaps) within mixedwood stands. The mosaic of canopy patches leads to different micro-habitat conditions for understory species, allowing for communities that include both early and late successional species and contributing to greater understory diversity. This study suggests that the mosaic of small canopy patches within mixed forest stands resembles a microcosm of the boreal mixedwood landscape, across which understory community composition varies with canopy composition at the stand scale. Second, I investigated the hierarchical organization of understory diversity in relation to the heterogeneous mosaic of canopy patch types through additive partitioning of diversity. The largest proportion of species richness was due to turnover among patches within patch type while individual patches had higher evenness. The mosaic of canopy patch types within mixedwood forests likely plays a crucial role in maintaining the hierarchical levels at which understory diversity is maximized. Third, I examined interactions among understory plant species by investigating the effect of shrub removal on biomass, composition and diversity of herbs using a 3-yr removal study in a natural understory community. There is asymmetric competition for light between erect shrub and herb species but herb response to erect shrub removal was species-specific. Plant interactions play an important role in structuring boreal understory communities. Finally, I explored the relative influence of space, environmental variables, and their joint effects, on understory composition and richness. The environmental variation caused by small canopy patches and biotic processes, such as species interactions, converge at the fine scale to create a spatially patchy structure in understory communities in boreal mixedwood forests. Modifications in the natural mixture of small canopy patches could disrupt the spatial and environmental structures that shape understory composition and diversity patterns. / Forest Biology & Management