Improving Wildflower Longevity in Roadside Seeding Areas

Re-vegetation efforts on bare roadsides of newly-constructed highways are primarily focused on the stabilization of soil to reduce rates of erosion. The Nebraska Department of Roads (NDOR) seeds the roadsides with a diverse mixture of grasses and wildflowers for site stabilization as well as to enhance the visual quality of roadsides. Although grasses dominate roadside plantings in terms of cover and density, wildflowers are largely responsible for the visual enhancement of recently-seeded roadsides. In addition to the visual component, wildflowers provide essential ecological functions on roadsides. Wildflowers improve water and nutrient cycling in the compacted roadside soils by increasing water infiltration and nutrient availability. Leguminous wildflower species increase nitrogen content of soil. The variability of wildflower leaf size, shape and orientation provides a more continuous soil cover than grass alone. The diversity of wildflower growth habits and life cycles also allows for a greater range of stand establishment and persistence when compared to sites seeded to only grasses. Federal guidance states that wildflowers are to be used in roadside seeding mixtures. Wildflowers compose about 10% of the total seeds in the seeding mixtures used by NDOR. Wildflower seeds are relatively expensive; therefore, despite the low percentage of wildflowers in the seeding mixtures, they represent 30% of the total cost of seed. Staff of NDOR report that wildflower density of most roadside seeding projects is acceptable in the first 2 or 3 years after seeding, but that wildflower density and cover decline in the following years. A recent study completed by the University of Nebraska-Lincoln in collaboration with NDOR has shown that wildflowers compose less than 10% of the botanical composition of highway roadsides 10 years following seeding. The study showed that the mature seeded stands along Nebraska highways are clearly dominated by seeded native grasses and invasive grasses, with only a few species of seeded wildflowers appearing occasionally. The common native grasses (e.g., Panicum virgatum) used in the NDOR seeding mixtures germinate and establish more readily than most native, perennial wildflowers included in the seeding mixtures. These grasses have higher germination rates, are well-adapted to a diversity of soil conditions, and grow rapidly following germination; therefore, they are able to out-compete most wildflowers when they are seeded in the same area. In some cases, however, wildflower presence in recently seeded, mixed stands can be enhanced by increasing the density or availability of wildflower seeds and/or spatially segregating the grass and wildflower seeds at seeding. The density or availability of seeds can be increased by using higher seeding rates or by establishing other sources of propagules or seeds, such as wildflower islands. Wildflower islands refer to small blocks within the area to be established that are seeded to wildflowers only. These localized areas seeded to wildflowers have the potential to remain as a dense stand of wildflowers and provide a source of seeds and propagules for wildflowers in the overall stand. When seeding new sites, the separation of grass and wildflower seed into separate rows has been shown to improve wildflower establishment by reducing the competition for resources between seedlings. Research in grassland ecology has shown that wildflower diversity declines over time because the grasses are more competitive when natural disturbances are removed from the ecosystem. In grassland systems, common natural disturbances are burning and the trampling and defoliation associated with grazing. The significance of disturbance is made evident by the relatively high plant diversity of grasslands periodically exposed to disturbances. Disturbances (e.g., grazing and/or burning) tend to favor wildflowers because they suppress grasses, thus opening areas and providing wildflowers greater access to water, nutrients and light interception. Burning or grazing roadsides in Nebraska is not realistic; however, mowing can be used as a reasonable substitute for grazing. The trampling effect and the patchiness of defoliation associated with grazing are difficult to replicate with mowing but the timing and intensity of defoliation can be manipulated with mowing. Research has shown that mowing or grazing at specific times and heights during the year can greatly impact plant communities by reducing the competition between grasses and wildflowers. The purpose of the proposed research is to test different strategies for establishing and maintaining wildflowers in roadside stands. In the first study, the interacting effects of the following seeding practices on the establishment of wildflowers in seeded mixtures of grasses and wildflowers will be determined: (1) increasing seeding rates of wildflowers, (2) segregating wildflower seeds from grass seeds in alternating rows when drilling the seed mixture, and (3) developing wildflower islands at the time of seeding. A second study will be conducted on recently established roadsides (4 to 6 years old) with fair to good wildflower composition. The objective of the study is to determine wildflower persistence in roadside stands in response to (1) interseeding of wildflowers, (2) timing of mowing, and (3) height of mowing.


    • English


    • Status: Active
    • Contract Numbers:

      SPR-P1(13) M329

    • Sponsor Organizations:

      Federal Highway Administration

      1200 New Jersey Avenue, SE
      Washington, DC  United States  20590

      Nebraska Department of Roads

      1500 Highway 2
      Lincoln, NE  United States  68502
    • Project Managers:

      Thompson, Art

      Soper, Nick

      Wienhold, Carol

      Poe, Ron

    • Performing Organizations:

      University of Nebraska, Lincoln

      527 Nebraska Hall
      Lincoln, NE  United States  68588-0529
    • Principal Investigators:

      Wienhold, Carol

      Soper, Jonathan

      Schacht, Walter

    • Start Date: 20120401
    • Expected Completion Date: 20170331
    • Actual Completion Date: 20161231
    • Source Data: RiP Project 31814

    Subject/Index Terms

    Filing Info

    • Accession Number: 01560329
    • Record Type: Research project
    • Source Agency: Nebraska Department of Roads
    • Contract Numbers: SPR-P1(13) M329
    • Files: RiP, STATEDOT
    • Created Date: Apr 11 2015 1:01AM