Ecological Restoration on Roadsides: Examining Ecological and Organizational Feasibility

Abstract

Highways and their vegetated easements are associated with several ecological and environmental problems. Ecological restoration on roadsides holds potential to ameliorate some of these by providing erosion control, improving landscape connectivity, and providing habitat for insects and other wildlife. However, due to both ecological and organizational constraints, roadsides are a challenging environment to restore. In particular, criteria for selecting appropriate sites and species for restoration are needed. In order to help meet this need, we transplanted seedlings of nine grassland species onto plots on eight highway interchanges surrounding Ann Arbor, Michigan. We tested the hypothesis that generalist species would outperform specialist species. We quantified two estimates of ‘niche breadth’ for each species, using the plants’ coefficients of conservatism and the number of U.S. counties in which each species is known to occur. We measured seedling survival, height, and biomass during the first growing season, as well as survival one year after transplant. We also quantified several ecological variables at each site in order to determine which of these predicted plant survival on interchanges. Neither index of niche breadth was a useful predictor of survival; though survival varied by species and by interchange. Plants were more likely to survive in sandier soils than those rich in silt or clay, with high bulk density, and high pH and conductivity. Temperature and humidity were near-significant predictors of survival, with survival positively associated with higher average humidity and lower average temperatures. Michigan has the potential to institute a restoration-oriented roadside vegetation management program. Policy related to roadside vegetation management, at both the federal level and in Michigan, has gradually become more ecologically-focused, though much of this has iii yet to be realized in practice. Using efforts in Iowa as a model, this study concludes by providing specific logistical considerations for transportation department officials in Michigan related to roadside re-vegetation using native plants.