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Chapter 9
Roadside Vegetation Management
9.2. Growing Threats Drive Expansion of DOT Invasive Species Practice

Management of invasive vegetation in the right of way increasingly impacts state DOT budgets. Invasive species are those non-natives introduced from another region or country. Transported to a new location, such species left behind their natural competition and began to crowd out native species and natural communities, leading to declining diversity, species rarity, agricultural impacts, and management problems. The large majority of non-native species - those occurring in locations beyond their known historical natural ranges and/or brought in from other continents, regions, ecosystems, or habitats-- do not pose a threat to the natural or human systems in which they are introduced; however, a small percentage of non-native species that do establish have the potential to become invasive and to cause significant economic, environmental, and human health consequences. [N] After introduction in a new environment, invasive species may establish easily and quickly, compete aggressively, and grow rapidly, presenting a threat to native species and habitats.

Executive Order (EO) 13112, "Invasive Species" defines invasive as "alien (non-native) species whose introduction does or is likely to cause economic or environmental harm or harm to human health." [N] Invasive species can be plants, animals, and other organisms (e.g., microbes). As transportation corridors enable people and vehicles to move from place to place, highways have become pathways or vectors for the spread of invasive. Construction ground disturbance also has the potential to reduce native species viability if invasive species are not managed prior to or doing construction, non-infested topsoil is not saved, or inadequate attention is given to revegetation with native species.


9.2.1 DOT Drivers, Obstacles, and Priorities Point to Areas of Needed Best Practices
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DOTs driving concerns and objectives in controlling invasive species include cost efficiency, reducing herbicide use, protecting rare or threatened species, and carrying out formal roadside vegetation management plans, and even pavement preservation. [N] Many DOTs were quite vocal about the obstacles confronting control of invasive species. For many, a simple lack of resources -both dedicated funding and dedicated personnel- lie at the heart of insufficient invasive species control. As NYSDOT stated, "[c]urrently, staffing and funding for invasive species management must compete against other priorities for the same staff time and funds - dedicated line items and a separate funding source would be a great benefit." Fifty-three percent of responding DOTs cited lack of state funds as an obstacle in invasive species control. Fifty percent cited a lack of control over lands adjacent to the ROW. Thirty-eight percent said limited federal highway funds were an obstacle to invasive species control. In addition states have varying definitions of invasive species and little legal impetus or guidance for addressing invasive species control. Many states' laws still only address noxious weeds identified for agricultural purposes. Thirty-five percent of responding DOTs cited differing priorities of federal, state and local agencies as obstacles to invasive species control. Inadequate or incomplete inventories of invasive, as well as means to track those identified remain obstacles for others.

Lack of templates or guidance on invasive species management is an obstacle for 33 percent of responding DOTs, while finding suitable native ground covers and the perception of native grasses as being difficult or slow to establish are issues for 28 and 30 percent, respectively.

Other obstacles cited by individual DOTs include the additional cost imposed by best practices such as equipment washing, the difficulty of monitoring such measures, the lack of specific guidelines or policies on a programmatic scale, poor and compacted soils, disturbed and degraded roadsides, and lack of an easy (commitment) tracking system for segments of ROW that come under federal funding for purposes of compliance with E.O. 13112 (with status easily accessible to maintenance personnel as projects close and landscaping and maintenance projects start and close). Getting the right information to the right people was a concern for some DOTs. As one put it, the problem is "[l]ack of communication, lack of training for contractors and overall lack of awareness in the organization, especially in that this is a serious issue." Others lack good training materials or management guidelines. DOTs also noted that access to information about the costs and benefits of treating invasive species could bolster their ability to get resources allocated to address the problem. Some of the key available information in this area is described or referenced below, by weblink if available. NCHRP Synthesis project 36-05 will go into greater detail on these topics.


9.2.2 Inadequate Action to Control Invasive Species Creates Heavy Costs
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In the United States, nonindigenous species do more than $130 billion a year in damage to agriculture, forests, rangelands, and fisheries, as estimated by Cornell University biologists. [N] Managers on Department of the Interior and other public lands, as well as the private sector, rank invasive species as their top resource management problem. [N] Estimates of current infestation on federal lands are in the range of 35 million acres (around 5 percent) on BLM lands alone; [N] however, at the estimated rate of expansion (5-15 percent/annually), the acreage infested doubles roughly every nine years. [N] The threat posed by this rate of expansion is enormous, in terms of lost natural resource values, economic production, and cost. By 2040, without substantial investment to stop the spread of such weeds, over 50 percent of federal land could be infested. [N] For DOTs, increasing roadside management costs are felt in terms of additional mowings, herbicide inputs, and labor, as well as the pressure to respond to public complaints.

Former Secretary of the Interior, Bruce Babbitt, noted that "[t]he invasion of noxious alien species wreaks havoc on America's environment and economy that is matched only by damage caused by floods, earthquakes, mudslides, hurricanes, and wildfire." [N] Introduced organisms are the second greatest cause, after habitat destruction, of species endangerment and extinction worldwide. [N] Invasive species are a factor in the decline of 49 percent of all imperiled species. [N] According to an Office of Technology Assessment study, just 79 of these non-native species cost the American public some $97 billion in damages to natural resources and lost industrial productivity during the 20th century. [N] These costs arise from a variety of factors: [N]

  • Contamination or competition with crops.
  • Decrease in forage value of rangeland and pastures.
  • Displacement of valuable wildlife habitat and disruption of food chains.
  • Elimination of waterfowl migration stops.
  • Reduction in property values and ability to acquire loans.
  • Alteration of ground water reserves.
  • Change in aesthetics of the landscape and degradation of natural heritage and educational value.
  • Increased fire threats.
  • Compromise of roadside visibility and safety.
  • Attraction of wildlife to roadside.
  • Additional costs of roadside maintenance.

The above costs are rising as invasive plants spread into another estimated 4,600 acres daily. [N] In a 2002 report entitled, Invasive Species: Clearer Focus and Greater Commitment Needed to Effectively Manage the Problem, the U.S. General Accounting Office (GAO) found that most economic estimates do not consider all of the relevant effects of nonnative species or the future risks that they pose, but that more comprehensive analysis could help decision makers make better resource allocations; i.e., allocate more resources to the task.

Other efforts by states, associations, and scientific entities to begin to document cost-benefit data for invasive species control include: [N]


9.2.3 Utilizing Flexible Funding for Maintenance Planning to Control Invasive Species
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Federal funds with regard to construction and maintenance may be used for new and expanded invasive species control efforts under each state DOT's roadside vegetation management program, including:

  • Statewide, right-of-way inventories of vegetation that map existing invasive plant infestations.
  • Inspection and cleaning of construction equipment.
  • Commitments to ensure the use of invasive-free mulches, topsoils and seed mixes.
  • Eradication strategies to be deployed should an invasion occur.

Multiple Executive Orders have directed federal agencies to address invasive species concerns and refrain from actions likely to increase invasive species problems. It also directs agencies to "provide for restoration of native species and habitat conditions in ecosystems that have been invaded." FHWA's implementing guidance specifies that: [N]

  • Federal funds cannot be used for construction, revegetation, or landscaping activities that purposely include the use of known invasive plant species as listed by some states or the National Invasive Species Council.
  • NEPA analyses require determinations of the likelihood of introducing or spreading invasive species and a description of measures being taken to minimize their potential harm.

A number of DOTs have started completing invasive species surveys for all projects (state and federal) with ground disturbing activities. If weeds are found and adjacent lands are federal, the DOT coordinates with that agency for more effective control of invasive species. Special mitigation measures to prevent the spread of weeds found and to prevent the introduction of invasive species are incorporated into NEPA documentation and contract specifications. Coordination among environmental, design/landscape architecture, and construction staff is on the upswing, addressing environmental impacts and eradication and control of invasive species during and after construction. At New York State DOT (NYSDOT) and Utah DOT (UDOT), for example, the departments are including invasive species in NEPA decision-making processes, documenting potential environmental impacts, and listing appropriate best management practices as mitigation commitments for all projects that have the potential to spread or introduce listed weeds.


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Continue to Section 9.3 »
Table of Contents
Chapter 9
Roadside Vegetation Management
9.0 Introduction
9.1 Inventory of and Management for Rare Species and Sensitive Resources in the ROW
9.2 Growing Threats Drive Expansion of DOT Invasive Species Practice
9.3 Practices for Prevention of Roadside Infestations
9.4 Statewide Inventory of Invasive or Noxious Species in the ROW and Update of Databases
9.5 Planning for Invasives Control
9.6 Roadside Vegetation Control Methods and Resources
9.7 Management of Visual Quality of the Roadside
9.8 Staffing, Training, & Partnerships
Lists: Examples | Tables | Figures
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