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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Public Roads - March/April 2000

Beware of Invasive Species

The following is adapted from several Department of Transportation sources, primarily Roadside Use of Native Plants, a handbook published by the Federal Highway Administration. Roadside Use of Native Plants provides state-by-state references on the use of native plants and how they can be used to benefit highway projects.

Beware of invasive species. No, we are not talking about aliens from outer space. Invasive species are plants and animals that are introduced into new areas in which they are not among the native flora and fauna, and because they no longer face the natural enemies or competition from their place of origin, they spread or reproduce prolifically. Invasive species can be a very, very big problem.

Non-native species can cause significant changes to ecosystems, upset the ecological balance, and cause economic harm to our nation's agricultural and recreational sectors. For example, introduced plants, such as kudzu in the southeastern states and purple loosestrife throughout the country, have choked out native plant species and consequently have altered wildlife and fish habitat. Zebra mussels introduced into the Great Lakes in the ballast water of cargo ships have colonized water pipes, boat hulls, and other surfaces, wreaking havoc on water systems, transportation, and native shellfish.

Each year, approximately $23 billion nationwide is lost to the effects of invasive plants on agriculture, industry, recreation, and the environment. An estimated 1860 hectares (4600 acres) of land are invaded daily by invasive plants.

Fighting Back

Purple loosestrife and reed canary grass are invasive plants that compromise wetland mitigation projects.

On Feb. 3, 1999, President Clinton signed Executive Order 13112, which directs the agencies of the executive branch of the federal government to work to prevent and control the introduction and spread of invasive species. Species that are likely to harm the environment, human health, or the economy are of particular concern. The executive order builds on the National Environmental Policy Act (NEPA) of 1969, the Federal Noxious Weed Act of 1974, and the Endangered Species Act of 1973 to prevent the introduction of invasive species; provide for their control; and take measures to minimize economic, ecological, and human health effects.

The U.S. Department of Transportation (DOT) plays a large role in the government's fight against invasive species because transportation systems can facilitate the spread of plant and animal species outside their natural range, both domestically and internationally. DOT has traditionally been in the forefront of national efforts to prevent and control the introduction of invasive species. For some time, DOT has had a strategic goal of protecting the natural environment; has adhered to statutory mandates and directives, such as the 1994 Presidential Memorandum on Environmentally and Economically Beneficial Landscaping Practices; and has participated actively on interagency committees, such as the Federal Interagency Committee for Management of Noxious and Exotic Weeds (FICMNEW), the Native Plant Conservation Initiative (NPCI), the Interagency Ecosystem Management Task Force, the Aquatic Nuisance Species Task Force, and the Interagency Working Group on Endangered Species.

On April 22, 1999, Secretary of Transportation Rodney E. Slater issued a "Policy Statement on Invasive Alien Species," which directed DOT's operating administrations to proactively implement Executive Order 13112.

The Federal Highway Administration (FHWA) is very active in the effort to control and prevent the spread of invasive species because highway corridors provide opportunities for the movement of invasive species through the landscape. Invasive plant or animal species can move on vehicles and in the loads they carry. Invasive plants can be moved from site to site during spraying and mowing operations. Weed seed can be inadvertently introduced into the corridor during construction on equipment and through the use of mulch, imported soil or gravel, or sod. Some invasive plant species might be deliberately planted in erosion control, landscape, or wildflower projects. Millions of miles of highway rights-of-way traverse public and private lands. Many of these adjacent lands have weed problems, and the highway rights-of-way provide corridors along which these noxious and exotic weeds can spread.

In its continuing effort to protect the environment, FHWA is promoting the use of native plants to help control the introduction of invasive species of plants.

"We are committed to protecting the environment along the nation's highways," said Federal Highway Administrator Kenneth R. Wykle. "Native plants are particularly useful for this because they can thrive in all parts of the country and also help preserve our natural heritage for future generations."

Wykle said that native plants can be used for erosion control, landscaping, and maintenance of highway rights-of-way. Native plants have adapted over time to the varied climates and geology that highway projects cross; can prosper without fertilizers; and, once established, can ward off the invasion of weeds, thereby reducing the need for herbicide use.

Oregon's shared equipment crosses county and state lines to control weeds.


FHWA developed some guidance for implementing the executive order. The guidance, released on Aug. 19, 1999, provides a framework for preventing the introduction of and controlling the spread of invasive plant species on highway rights-of-way. Controlling invasive plants on rights-of-way can often be a complex effort involving various governmental jurisdictions, adjacent landowners, and the general public. FHWA's guidelines were developed with the goal of promoting improved cooperation, communication, and joint eradication efforts with agencies at all levels and with the private sector. To reduce economic and ecological costs and to improve eradication effectiveness, states may wish to incorporate elements of this guidance into their planning and implementation of construction, erosion control, landscaping, and maintenance.

Use of Federal Funds

Under the executive order, a federal agency cannot authorize, fund, or carry out actions that it believes are likely to cause or promote the introduction or spread of invasive species in the United States or elsewhere unless all reasonable measures to minimize risk of harm have been analyzed and considered. Complying with the executive order means that federal-aid and Federal Lands Highway Program funds cannot be used for construction, revegetation, or landscaping that purposely includes the use of known invasive plant species.

The executive order established a National Invasive Species Council, and until an approved national list of invasive plants is defined by the council, "known invasive plants" are defined as those listed on the official noxious weed list of the state in which the activity occurs. FHWA recommends use of federal-aid funds for new and expanded invasive species control under each state's roadside vegetation management program.

FHWA NEPA Analysis

A determination of the likelihood of introducing or spreading invasive species and a description of the measures being taken to minimize their potential harm should be part of any process conducted to fulfill agency responsibilities under NEPA. Consideration of invasive species should occur during all phases of the environmental process to fulfill the requirements of NEPA. For example, at the very beginning of the project, discussions with stakeholders should identify the potential effects from invasive species and include possible prevention and control measures.

The actual NEPA analysis should include the identification of any invasive terrestrial or aquatic species -- plant or animal -- that could do harm to native habitats within the project area. This could involve mapping all existing invasive populations on and adjacent to the project and a survey of existing soils for invasive potential. Also, the analysis should include the potential effect of the disturbances caused by construction on the spread of invasive species. Finally, the analysis should include a discussion of any preventative measures or eradication measures that will be taken during the project. Measures may include inspecting and cleaning construction equipment; ensuring the use of invasive-free mulches, topsoils, and seed mixes; and developing eradication strategies to be deployed should an invasion occur. Until the National Vegetation Management Plan specified in the executive order is completed, NEPA analyses should rely on each state's noxious weed list to define the invasive plants that must be addressed and the measures to be implemented to minimize their harm.

State DOT Activities

With the help of county weed manager Richard Sebastian, elementary school children raise and release beatles to control purple loosestrife on a Minnesota DOT right of way.

Under the executive order, state departments of transportation have new opportunities to address roadside vegetation management issues on both their construction and maintenance. Through new levels of cooperation and communication with other agencies and with conservation organizations on all levels, the highway programs offer a coordinated response against the introduction and spread of invasive species.

FHWA strongly encourages statewide, right-of-way inventories of vegetation that map existing invasive plant infestations to provide information for NEPA analysis. In addition, FHWA encourages state DOTs to develop their own vegetation management plans and their own statewide invasive plant inventories based on the executive order and the national plan, when it is available. In the absence of a specific state plan, the national plan will serve as policy and guidance for the state.

FHWA encourages the state DOTs to implement the Executive Memorandum on Beneficial Landscaping at every opportunity. This includes applying it to highway landscaping projects, rest area construction, scenic overlooks, state entrances, and transportation enhancement activities. In addition, FHWA recommends that roadside maintenance programs be given the necessary support to control and prevent invasive species.

Innovative Design

FHWA encourages the selection of construction and landscaping techniques and equipment that will contribute to accomplishing the intent of the executive order. These include bio-control delivery systems, more efficient equipment cleaners, improved seeding equipment for steep slopes, safer burn-management equipment, easier-to-use geographic positioning systems to map existing invasive populations, and methods to minimize soil disturbance during vegetation management activities to reduce the opportunities to introduce invasive species.

Coordinated Research

The FHWA environmental research program will promote studies on methods to control invasive plants and to restore native species. FHWA will also make a concerted effort to support applied research relevant to the vegetation management programs of the state DOTs. Research results will be shared with the state DOTs and other state and federal agencies.


FHWA suggests additional training in integrated vegetation management principles for vegetation managers in the maintenance districts, landscape units, and erosion-control sections of each state DOT. FHWA will provide materials for training in the identification of invasive plants and the restoration of native plants. FHWA also encourages regional workshops at its four national resource centers.

FHWA supports efforts by the state agencies to increase public awareness about invasive plants and animals and the integrated management methods being used to control and prevent the spread of invasive species.

Interagency Cooperation

Vegetation management in Iowa begins with planting non-invasive plants.


FHWA recommends that state DOTs participate in state invasive species councils, as they are established. These interagency councils will probably include federal agencies, state agencies, and local and tribal governments. Many states have already begun to organize these councils to promote cooperative work on invasive species issues within their state. These groups can share public awareness, training, databases, policy, and research information and can be a resource for the National Invasive Species Council.

Each state DOT should also work with adjacent state DOTs to establish coordinated prevention and control measures for invasive species.

State Models That You Can Use

Some state DOTs have already taken action. For example:

  • Georgia, Maryland, Utah, and Puerto Rico have already put together intra-agency and interagency task forces to assess the problem and determine how to apply the guidance provided by FHWA to their policyand planning.
  • Wyoming and surrounding states agreed to use only weed-free mulches on construction and upgrade projects.
  • Florida's departments of transportation and agriculture have partnered to certify weed-free sod on their projects.
  • Oregon DOT requires the washing of equipment moving into and out of a construction site.

A model partnership is found in Oregon. The state DOT supplies the truck. The Bureau of Land Management supplies the sprayer. The county provides the driver/applicator. Their combined knowledge of weed locations, equipment, and willingness to work together make them an exemplary partnership. Just ask the local ranchers!

Some states are taking steps to avoid the planting of invasive plants in the first place. Many non-native quick-cover plants have turned out to be weed problems over time. Some cool-season native grasses are being tried as quick cover to provide erosion control and to eliminate water quality issues and other problems.

Understanding the Weed Problem

After conducting an inventory of vegetation in the state, Caltrans (the California Department of Transportation) developed vegetation preservation and management plans.

Recognizing invasive species and understanding the problems they cause are critical to minimizing the problems. If the public understands this issue, states should find more support for weed prevention and control. If maintenance crews are better trained about invasive species, they will be able to spot problem plants before the plants spread. If contractors and design teams know which plants cause problems, they can avoid planting them or disturbing sites in the first place. If we partner with our neighbors, we can do so much more. If we follow up with planting native plants, weeds will be discouraged naturally.

FHWA Handbook

FHWA recently published a handbook, Roadside Use of Native Plants, with state-by-state information to aid in the use of native plants. After weed control, planting native plants on sites has worked in some states to prevent the further spread of weeds or at least to reduce the problem so that methods such as spot-spraying can be effective.

Preserving the native plants that exist on rights of way should be a priority. When these remnants are invaded by weeds, the weeds should be controlled as quickly as possible. Since plants do not understand political boundaries, states should work together to share information and equipment to halt the spread of invasive plants.

FHWA is developing a sequel handbook, Roadsides and Invasive Species. This new book will explain noxious weed law, and it provide species lists and the policies of all 50 states. The handbook should be distributed in early 2001.


"The executive order and the FHWA guidance is proactive, practical, and on target," said Bonnie Harper-Lore, FHWA's vegetation manager. "Now, it's important that all of us in the transportation right-of-way management business do our part. Like many, I have attended weed meetings for 20 years, but this executive order is the first meaningful national response that I have seen. It should go down in history as a turning point in our 'war on weeds.'State DOTs are definitely part of the solution to gaining control of invasive species. I have traveled with too many state vegetation managers who did not have the resources to do what is needed. This 'do more with less' situation can now change. Although some invasive plants may be beyond control, all agencies united at every level should be able to stop or contain some alien invaders, especially new invaders."

For more information about FHWA's efforts to fight invasive species and restore native plants, please contact Bonnie Harper-Lore at (651) 291-6104 or or visit the Web site at

The 665-page handbook Roadside Use of Native Plants includes vegetation maps and lists of native trees, shrubs, vines, grasses, and other plants indigenous to each state. In addition, the handbook lists environmental, academic, scientific, and other organizations in each state. Requests for copies should be sent to Fred Bank, Federal Highway Administration, HEPN-30, Room 3240, 400 7th Street SW, Washington, DC 20590, or via e-mail to Bonnie.Harper-


  1. Randy G. Westbrooks. Invasive Plants, Changing the Landscape of America, the Fact Book, Federal Interagency Committee for the Management of Noxious and Exotic Weeds, Washington D.C., 1998. (Copies are available from the U.S. Government Printing Office. Call (202) 512-1800 to order.)
  2. John M. Randall and Janet Marinelli, editors. Invasive Plants, Weeds of the Global Garden, Brooklyn Botanic Garden, New York, N.Y., 1996. (To order, call (800) 827-8673.)
  3. Michael J. Grodowitz and Al Cofrancesco. "PMIS, Plant Management Information System for Noxious and Nuisance Plants," a CD-ROM, 1998. (To order, call (601) 634-2972.)
  4. Bonnie Harper-Lore, editor. Roadside Use of Native Plants, Federal Highway Administration, Washington, D.C., 1999.