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.
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