Comparison of Native Grasses to Traditional Plantings for Roadside Stabilization
Invasive Species/Vegetation Management
Research Idea Scope
Stabilization of roadsides after construction is critical to protecting water quality, public safety and the longevity of the project. Unfortunately, current erosion control seed mixes include invasive exotic species. The standard planting mix is comprised of Sericea lespedeza (Lespedeza cuneata), Bermuda grass (Cynodon dactylon), Tall fescue (Festuca arundinacea), and Bahiagrass (Paspalum notatum). These species establish quickly and hold soil well but are also four of the top ten invasive species in the Southeastern United States. Using them for soil stabilization has allowed them to spread beyond roadsides and into many pristine habitats such as state parks and national forests. It also contributes to the high cost of invasive species control and eradication.
The Georgia Department of Natural Resources (DNR) and the Georgia Department of Transportation (DOT) have teamed up to investigate alternatives. An earlier partnership between Georgia Power and the DNR used native warm season grasses to stabilize soil in power-line construction areas and found that one species in particular, switchgrass (Panicum virgatum), established more quickly, held soil more effectively, and tolerated drought better than the traditional mix of exotics species. Furthermore, it was easy to establish through most of the year and cost less than the traditional mix. Photos of these field trials are available for review.
After these trials, the DNR adopted switchgrass plantings for most erosion control projects, including wetland restorations, logging decks, soil stabilization after logging steep slopes, and around new buildings. Georgia Power has also continued using native grasses on several sites.
One obstacle to a wider adoption of this new technology is the widespread acceptance of the exotic species plantings, particularly among contractors. The traditional mix is well known and tested. The current methods were established in an era long before invasive exotic species were recognized as a threat and are rarely questioned today.
We propose to plant the traditional mix side by side with switchgrass in areas of high visibility. Educational signage detailing the planting methods and costs would be erected and the area used as a training site for new contractors. It is our hope that with greater exposure these new techniques will gain in popularity, eventually replacing the use of exotic species.
Urgency and Payoff
This research will develop an alternative to our current invasive exotic species seed mix that can lower the cost of construction and improve roadside slope stability. Based on earlier trials, switchgrass established more quickly, grew faster and had deeper roots and larger root masses than the exotic mix. Replacing our exotic invasive plant species with a native alternative will help to stop the practice of introducing invasive species into the environment. This will support the on-going and costly fight to control the spread of these invasive species. Planting a native species will also improve the ecological health of roadside corridors.
In addition, this practice will improve the aesthetics of our roadsides, as many people prefer the look of native grasses over exotic species. Many native species have been widely planted in the Midwest along interstates and roadsides as prairie restoration areas. The replacement of exotic species by native species for soil stabilization will reduce the ecological impact of construction, improve water quality, reduce the costs to taxpayers, and improve the aesthetics of our roadsides.
Jaime Collazo, Georgia Department of Transportation