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Slope Restoration on Urban Freeways
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2021-08-11
[PDF-2.09 MB]
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Edition:Final Report
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Abstract:Diverse plantings along freeway roadsides can be beneficial to surrounding areas in many ways, such as improved driver safety, increased biodiversity, and improved aesthetics. Unfortunately, establishing these plantings can be difficult for a variety of reasons. To improve the success of future plantings, the authors investigated the impacts of site preparation and plant selection on the success of roadside plantings. The objective of the study was to evaluate the effect of site preparation (tillage and addition of compost) on establishment of roadside plantings and to identify suitable plants for roadside plantings. The authors conducted a large-scale field study at two locations (Warren, MI and Roseville, MI) along I-696 near Detroit, MI. They installed 16 selections of shrubs and perennials into sites with four different site preparation treatments. In a separate trial on the site, they evaluated 16 additional selections of shrubs and perennials to identify additional plants suitable for roadside plantings. In the site preparation experiment, compost application had positive effects on plant growth and plant coverage (% ground cover) in 2019 and 2020, irrespective of tillage. Soil surface tillage had no effect on overall plant coverage, plant growth and plant survival for most species. Evaluation of plant moisture stress and plant nutrition suggests that the addition of compost improved plant growth and establishment through improved soil nutrient content rather than improved moisture availability. Overall, the compost only site preparation treatment was the most successful in improving plant establishment and aesthetics. Plants grown in plots with 4 in compost as a top-dress, followed by 3 in of mulch grew as well or better than plants in other treatments. This site preparation method is consistent with current MDOT standards. These results emphasize the need for contractors to adhere to standards during plant installation. Based on the results of this project, site preparation and plant selection guidelines were updated and incorporated in a new Plant Selection Manual for the state of Michigan.
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