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Fall 2001

Greener Roadsides

Greener Roadsides archive

The Problem with Invasive Plant Species

The many conflicts and constraints for highway rights-of-way

Or should I have said problems? Here is my top ten list of problems each State Department of Transportation is faced with, when dealing with invasive plant species.

  1. No single definition embraced - For Federal dollars purposes, all agencies have agreed to the following definition: "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health" ..It is the best definition we have at this time. Although some native plants can act invasively, they are not considered invasive species. That does not mean we give a free pass to the use of all native plants. There are some that are toxic to animals and humans, as well as troublesome to agriculture. Choose plants carefully.

  2. State policy differences - Because some DOTs give the control of invasive plants a higher priority than their neighbors, conflicts will arise. State DOTs do complain about one another's lack of weed control, and/or planting of noxious weeds. State DOTs need to talk to one another; share their experiences; and consider border partnerships.

  3. Lack of funding - Key to the rapid spread of invasive plants is the lack of funding at every level, in every agency. Many State legislatures, Congress, and federal agencies are exploring ways of making funds available across the country. Beyond prevention and control, some of this funding needs to be directed towards public awareness and research efforts.

  4. Needed training - Eradicating a new invader avoids years of maintenance efforts needed to control a large, well-established population. Trained crews can identify and stop threats like yellow star thistle in its tracks. Arm them with the tools they need to fight this biological wildfire.

  5. Other agencies - Although 16 federal agencies signed a Memorandum of Understanding (MOU) in 1994 to encourage communication and cooperation, the reality in the field is not always consistent with the MOU. Our roadways cross those agencies' lands. Increased partnerships will be mutually beneficial.

  6. Public awareness - State DOTs are under various levels of public pressure over this issue. States like Tennessee are well organized under the Tennessee Pest Plant Council. More and more States are establishing such Councils. DOTs need to become members to learn the public and agency concerns. The public is likely to be surprised by many DOT efforts already in place.

  7. In the name of safety, maintenance methods can actually increase invasive plants. Most States bare-ground the areas around guardrail, inviting invasions. Frequent and low mowings stress grasses and allow weed invasion. If methods like blading expose soils, revegetate with natives quickly.

  8. One weed list - Complicating DOT and other agency cooperation is the absence of a list of key invasive plant species. Recognizing that different weed species require different control tactics, how can we pull together, if our efforts are not aimed at the same plants? Controlling your State's noxious weed list is only part of the answer. Focusing on already established invasives ignores new threats.

  9. Erosion control/water quality - Another constraint that DOTs face is law that requires quick establishment of vegetative cover to stop erosion and protect water quality. In our history of accomplishing quick cover, we have often chosen aggressive introduced grasses and legumes to do the job. They overdid the job! Careful selection of erosion control and wildflower mixes is important.

  10. Construction practices - Soil disturbances caused by construction, create new populations of weeds. Here are some best management practices (BMPs):
    1. Minimize soil disturbances to avoid future costly weed control,
    2. Inspect and wash equipment before moving to another site,
    3. Provide a construction pay item for cleaning, and other on-the-site work, and
    4. Avoid importing soils or mulches that contain weed seed.
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Questions and feedback should be directed to Marlys Osterhues (marlys.osterhues@dot.gov, 202-366-2052).

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