Center for Environmental Excellence by AASHTO
skip navigation
print icon Print

Invasive Species/Vegetation Management


This section provides an overview of invasive species and vegetation management issues facing transportation agencies. Information presented is drawn in part from National Cooperative Highway Research Program Synthesis 363: Control of Invasive Species (2006).

Sections in this Overview include:




The rights-of-way that border the nation’s roads include more than 12 million acres of land, and road maintenance crews are on the front line in managing the land and responding to and preventing invasive species infestations. Control of invasive plant species along America’s roadsides is an increasing concern for transportation agencies nationwide. 

The Federal Highway Administration (FHWA) described the unique issues transportation agencies face in addressing invasive species in 1999 guidance:

“Nonnative flora and fauna 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. Transportation systems can facilitate the spread of plant and animal species outside their natural range, both domestically and internationally. Those species that are likely to harm the environment, human health, or economy are of particular concern.”

“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, and sod. Some invasive plant species might be deliberately planted in erosion control, landscape, or wildflower projects. Millions of miles of highway rights-of-ways traverse public and private lands. Many of these adjacent lands have weed problems and the highway rights-of-way provide corridors for further spread.”

[back to top]

Laws, Regulations and Policies

Federal and state transportation agencies have been working for years to implement numerous laws and policies aimed at effective vegetation management, promotion of native plants and wildflowers, and control of invasive species in the nation’s transportation corridors.

The Surface Transportation and Uniform Relocation Assistance Act (1987) established mandatory requirements that native wildflowers be planted as part of landscaping projects on the Federal-aid highway system.

The Executive Memorandum on Beneficial Landscaping (1994) encouraged use of native plants as much as possible on all Federal lands and in all federally funded projects.

Executive Order 13112 on Invasive Species (1999) was adopted to encourage government agencies to prevent and control invasive species and to plant native species. The order set up a National Invasive Species Council, which was charged with producing a National Invasive Species Management Plan. The plan, completed in 2001, provides a blueprint for Federal agencies’ implementation of the executive order. In 1999, FHWA’s Guidance Implementing Executive Order on Invasive Species provided further direction for transportation agencies.

The Noxious Weed Control and Eradication Act (2004) requires the Secretary of Agriculture to develop a program that will provide financial and technical assistance to weed management entities to control or eradicate noxious weeds on public and private lands.  Transportation agencies partner with many of these organizations.

The Safe, Accountable, Flexible, Efficient Transportation Equity Act for the 21st Century (SAFETEA-LU, Pub. L. No. 109-42, 2005) was enacted, including provisions to address invasive species and noxious weeds in transportation projects. Specifically, Section 6006 of the law extends eligibility of funds under the National Highway System and the Surface Transportation Program to include control of noxious weeds noxious weeds and establishment of native species in transportation projects. 

[back to top]

FHWA Guidance

On May 16, 2006, FHWA issued Guidance on 23 U.S.C. §329 on the Control of Noxious Weeds and Aquatic Noxious Weeds and Establishment of Native Species, to implement SAFETEA-LU Section 6006. This guidance describes the activities eligible under the establishment and management of plants categories in the law. Transportation funds can be spent on the following eligible activities:

  • Right-of-way (ROW) surveys to determine management requirements to control Federal or state noxious weeds:
  • Establishment of plants, whether native or nonnative, with a preference for native to the maximum extent possible;
  • Control or elimination of plants (noxious weeds);
  • Elimination of plants to create fuel breaks for the prevention and control of wildfires; and
  • Training.

FHWA also provided specific direction to transportation agencies in its 1999 Guidance Implementing Executive Order on Invasive Species.  

The guidance requires National Environmental Policy Act (NEPA) documents to make a determination of the likelihood that projects may introduce or spread invasive species and then describe measures that will be taken to avoid and minimize potential harm from conception through construction.  In addition, FHWA encourages right-of-way inventories of vegetation, which can be used to identify rare species and natural habitats to be preserved as well as infestations of invasive species that need to be eradicated, along with tailored vegetation management plans. FHWA also recommends that roadside maintenance programs be given the necessary support to control and prevent invasive species. FHWA also encourages the selection of construction and landscaping techniques and equipment that will contribute to accomplishing the intent of the Executive Order.

Partial text of the guidance is excerpted below:


Under the E.O., State Departments of Transportation (DOTs) have new opportunities to address roadside vegetation management issues on both their construction activities and maintenance programs. Through new levels of cooperation and communication with other agencies and conservation organizations at all levels, the highway program offers a coordinated response against the introduction and spread of invasive species.

The E.O. 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 impacts. In response to the proactive policy of the Office of the Secretary of Transportation and the E.O., the FHWA offers the following guidance:

Use of Federal Funds:

Under the E.O., Federal agencies 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 E.O. means that Federal-aid and Federal Lands Highway Program funds cannot be used for construction, revegetation, or landscaping activities that purposely include the use of known invasive plant species. Until an approved national list of invasive plants is defined by the National Invasive Species Council, “known invasive plants” are defined as those listed on the official noxious weed list of the State in which the activity occurs. The FHWA recommends use of Federal-aid funds for new and expanded invasive species control efforts under each State DOTs’ roadside vegetation management program.

FHWA NEPA Analysis:

Determinations of the likelihood of introducing or spreading invasive species and a description of measures being taken to minimize their potential harm should be made 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, during scoping, discussions with stakeholders should identify the potential for impacts from invasive species and include possible prevention and control measures. The actual NEPA analysis should include identification of any invasive terrestrial or aquatic animal or plant species that could do harm to native habitats within the project study area. This could involve the mapping of 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 impact of the disturbances caused by construction on the spread of invasives. Finally, the analysis should include a discussion of any preventative measures or eradication measures that will be taken on the project. Measures may include the inspection and cleaning of construction equipment, commitments to ensure the use of invasive-free mulches, topsoils and seed mixes, and eradication strategies to be deployed should an invasion occur. Until the National Vegetation Management Plan specified in the E.O. 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. [Editor’s Note: The National Invasive Species Management Plan was completed in 2001.]

The FHWA strongly encourages statewide, right-of-way inventories of vegetation that map existing invasive plant infestations to provide information for NEPA analysis. In addition, the FHWA encourages the DOTs to develop their own vegetation management plans based on the E.O., their own statewide invasive plant inventories, and the National plan when available. In absence of a specific State or State DOT plans, the National plan will serve as policy and guidance to the States.

State DOT Activities and Funded Facilities:

The 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:

The FHWA encourages the selection of construction and landscaping techniques and equipment that will contribute to accomplishing the intent of the E.O. 13112. 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 for invasive population inventories, and methods to minimize soil disturbance during vegetation management activities so as to reduce the opportunities for the introduction of invasive species.

Coordinated Research:

The FHWA environmental research program will promote studies on invasive plant control methods, and restoration of native species after control. We will make a concerted effort to support applied research relevant to State DOT vegetation management programs. Results will proactively be shared among States and other State and Federal resource agencies.


The FHWA suggests increased training of vegetation managers in maintenance districts, landscape units, and erosion control sections within each State DOT. Integrated vegetation management principles should be included in this training. The FHWA will provide training materials for identification of invasive plants, and restoration of native plants, plus encourage regional workshops in its [national Resource Center]. The FHWA supports increased public education, especially resulting from interagency partnerships. State agencies are also encouraged to take steps to increase public awareness about invasive plant species and the integrated management methods used to control and prevent invasives.

Interagency Cooperation:

The FHWA recommends that State DOTs participate in State invasive species councils as they are established. These interagency councils will likely include Federal agencies, State, 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, data bases, policy, and research information and be a resource the National Invasive Species Council. The FHWA suggests that each State DOT cooperate with adjacent State DOTs to establish coordinated prevention and control measures for invasive species.

Interagency Committees:

The FHWA will continue to participate in the coordinated activities of FICMNEW, NPCI, and the Aquatic Nuisance Species Task Force (ANS). The FICMNEW initiates cooperative projects aimed at public awareness, policy, training, and research on invasive plant issues. The NPCI addresses non-native invasive species issues across agencies in an effort to protect and to restore native plant communities nationwide. The ANS focuses interagency efforts on those aquatic plant and animal species that impact our Nation’s waterways. The FHWA encourages participation by State DOTs in the State Interagency Invasive Species Councils.


[back to top]

Vegetation Management and Control of Invasives

E.O. 13112 mandated a risk-based approach, including consideration of the likelihood that an invasive species will establish and spread, as well as the degree of harm it could cause.  To do this, it helps to start with a master list of the transportation agency’s work activities that may inadvertently promote the spread of invasive species; a risk assessment identifies the most significant issues and helps decide where to focus. Construction projects, transportation systems, spraying and mowing operations can inadvertently spread invasives. Some common mechanisms may include:

  • Use of forage mulches that have not been certified weed-seed free mulches and other erosion control products.  
  • Planting of species now controlled as invasive for erosion control purposes, including aggressive sweet clovers, alfalfa, smooth brome, trefoil, and perennial rye. 
  • Allowing invasive species to exist on projects’ rights-of-way.  Failure to control an invasive species allows it to spread on and off the right-of-way.
  • Placement of spoil or importation of topsoil contaminated with invasive species, such as ragweed, thistles, and sweet clovers.
  • Ill-timed maintenance disturbances like blading, mowing, ditch dredging, and bare-grounding, which have been known to increase invasive species.
  • Indirect mechanisms such as drainage flows, wind, vehicles, people, and wildlife.
  • Movement of construction equipment from a weedy site to a non weedy site, which can transport undesirable seeds.

Best management practices (BMPs) are being used to reduce the introduction or spread of invasive species.

[back to top]

Risk Management, Prevention, and Inventory

The first line of defense and the most cost-effective strategy against invasive species is preventing them from invading and becoming established in the first place.  Once an infestation becomes well-established, management is expensive and eradication is very difficult.  Detection is one of the most important components of prevention of spreading invasive species.  The second most important is eradication before they produce seed or develop an established root system.  Transportation agencies and other agencies use a variety of risk management, business aspect identification, species and action prioritization, and mapping techniques to get ahead of invasive species and manage roadside vegetation as efficiently as possible.

Early detection and eradication are often performed where species can most easily gain a foothold (such as construction sites) or cause the most damage (intact natural areas).

Early detection consists of identifying and documenting the newly introduced invasive weed species in an area.  Then, rapid response may be employed to eradicate new infestations and methods may be taken to prevent movement to non-infested areas.   Early detection of incipient invasions and quick coordinated responses are needed to eradicate or contain invasive species before they become too widespread and control becomes technically and/or financially impossible.  Populations that are not addressed early may require costly ongoing control efforts.  For example, spotted knapweed (Centaurea biebersteinii) was introduced to Montana in the 1920s, and by 1988, had infested more than 4.7 million acres. The economic impact is approximately $42 million annually.

About a quarter of transportation agencies surveyed as part of NCHRP Synthesis 363: Control of Invasive Species have undertaken a statewide inventory of at least one invasive species in the ROW; however, nearly a third of responding DOTs say they do not plan to implement a statewide survey in the future due to concerns about cost.  DOT roadside invasive species inventories are all used to identify and locate areas for treatment, invasion by new species, and to set priorities. DOTs also indicated that inventories are being used to:

  • Partner with other agencies in providing funding for control of specific species.
  • Estimate expansion of weed presence and monitor treatment results and acres infested.
  • Guide and evaluate invasive species control efforts.
  • Guide effort/budgeting to meet established goals.

Prevention involves attention to the most common means of transmission, including contaminated seed, mulch, or soils; movement of unlearned equipment or machinery from an invasive weed-contaminated area to a non-contaminated area; and lack of restoration or revegetation after construction.  Prevention depends upon limiting the introduction of new weeds through:

  • Minimizing the disturbance of desirable plants and soils.
  • Maintaining desired plant communities through good management.
  • Monitoring high-risk areas such as transportation corridors and bare ground.
  • Revegetating disturbed sites with desired plants, such as plants from local natural areas. 
  • Evaluating the effectiveness of prevention efforts and adapting plans for the following year.
  • Early detection and eradication of small patches of weeds through regulatory inventory and corrective action.

A risk assessment process assesses species based on their perceived risk and potential impact.  The objective of assessment is to predict whether or not a species is likely to become established and be invasive and to generate a relative ranking of risk.  Processes for setting priorities often incorporate risk assessment. 

Monitoring the numbers of a pest species killed or removed is a measure of the work being done but is not a measure of invasive species control. Success of an invasive species control project can be measured by monitoring numbers of the pest species that remain, and ultimately the condition of the ecosystem they are in.  Removing an invasive alien species from an ecosystem will not automatically lead to the return of the indigenous flora and fauna.  While this is often the case, removal of one alien species may simply open the way for colonization by another. Monitoring of the impact of control actions needs to be put in place, preferably starting with small-scale activities to verify the impact of control operations, and if the results are not as expected, the management plan may need to be reconsidered and adapted. This may require additional flexibility in vegetation contracts.


[back to top]

Integrated Roadside Vegetation Management

Transportation agencies are taking a variety of steps to plan for vegetation management and share information across division areas and professional specialties, to address cross-cutting needs, and to take a more integrated approach to invasive species control. Information is often exchanged informally. Chief among the more formal approaches are development of organization-wide and district-specific integrated vegetation management plans.  Geographic Information Systems enable the locations of weed patches to be stored digitally, and allow treatments to be tracked, automatically administered in some cases, and assessed over time. 

Integrated Roadside Vegetation Management (IRVM) or Integrated Vegetation Management (IVM) encourages stable self-sustaining vegetation with limited use of mowing, herbicides, tree removal, and other methods as necessary.  Because no single tactic can solve a current weed problem or prevent future infestations, IVM encourages managers to combine several treatment methods into an integrated weed management program tailored to the site and resources available. In addition, such a program fosters communication and cooperation among the many individuals and agencies involved in right-of-way, construction, and vegetation management.  Integrated methods focus on the ultimate goal, which for transportation agencies may be preservation (or increase) of indigenous biodiversity as well as management of overall maintenance costs.  Planning helps achieve these ends and considers the range of control options.

The process of integrated control can be complicated, involving several different tactics in combination or in sequence, or it may involve one method. For example, cutting is frequently combined with chemical control to the stump, for woody invaders.  Control of purple loosestrife (Lythrum salicaria) may involve biological control, mechanical removal, and other methods. Consideration of the environmental impacts of control actions requires that environmentally sound methods be available and judiciously deployed, especially in highly vulnerable areas.  IVM has been described as a decision-making and management process that uses knowledge from a broad base of expertise, a combination of treatment methods, and a monitoring and evaluation system to achieve vegetation management goals.  Common steps in an integrated vegetation management plan are:

  • Understand pest and ecosystem dynamics.
  • Assess situation and management controls.
  • Identify the species of highest priority for a management program.
  • Set management objectives and tolerance levels.
  • Compile treatment options, including detailed information on methods for eradication, containment, control, and mitigation.
  • Account for economic and environmental effects of treatments.
  • Develop site-specific treatment plans.
  • Secure resources and implement training.
  • Monitor outcomes and revise and adapt management plans.

A successful control strategy for an invasive often begins with checking on-line and other data sources about management options for the target species.  Successful methods used under similar conditions, i.e., in similar habitats and climates, are preferred.   The most successful invasive species control has been achieved with species-specific methods, which also have the least impact on non-target species. In some instances, such as highly degraded habitats without any native species left, a more general method such as bull-dozing or a broad-spectrum herbicide is acceptable.  In less disturbed areas, in particular nature reserves, for example, the use of a species-specific method is highly recommended. Note that consideration needs to be given to pollinators because some species depend on specific pollinators for reproduction. Bulldozing could be a real problem for native ground-nesting bees for example.

In choosing a management strategy, transportation agencies usually consider:

  • Legal requirements related to management of invasive species and particular regulations on herbicide usage, including those in health and safety legislation.
  • Best methods that have been used for this target species.
  • The types of herbicides, baits and equipment that are readily available and the ways by which further supplies can be obtained.

More information on control methods and management strategies used by transportation agencies may be found in NCHRP Synthesis 363: Control of Invasive Species and AASHTO’s Compendium of Environmental Stewardship Practices, Policies, and Procedures.

[back to top]


Nearly 85 percent of transportation agencies (34 states) responding to a research survey performed as part of NCHRP Synthesis 363: Control of Invasive Species said they are working with others outside the agency to identify existing or emerging populations of invasives. Just 10 percent said they were not.  State transportation agencies are working with Weed Management Areas, regional associations and councils, other federal and state land management agencies, and entities that may be able to provide technical support or concrete assistance like agriculture departments, the U.S. Geological Survey, and various non-governmental organizations (NGOs).  The most common transportation agency partnerships for invasive species control are DOT participation on State Invasive Species Councils/Task Forces or state noxious weed committees.  Some transportation agencies work with another agency to have them review and treat the ROW, often the state Department of Agriculture and local weed and pest districts.

Transportation agencies also turn to nongovernmental organizations when they need assistance.  Links to Professional & Non-profit Organizations with an interest in invasive species control are available on-line.  State Natural Heritage Programs are available through NatureServe’s website.  A number of innovative partnerships have been developed.  Some of the most well-known are those with The Nature Conservancy.  New York State’s Adirondack Park Invasive Plant Prevention Program is one such example.

Additional examples may be found in NCHRP Synthesis 363: Control of Invasive Species

[back to top]

New - items posted in the last 7 days

skip navigation