Roadside Revegetation: An Integrated Approach to Establishing Native Plants and Pollinator Habitat

Chapter 7 – Operations & Maintenance

Table of Contents

• Chapter 1: Introduction
• Chapter 2: Initiation
• Chapter 3: Planning
• Chapter 4: Revegation Plan Example
• Chapter 5: Implementation
• Chapter 6: Monitoring
• Chapter 7: Operations & Maintenance
  • 7.1 Introduction
  • 7.2 Decision Process for Treating Unwanted Vegetation
    • 7.2.1 Inventory of Roadsides
    • 7.2.2 Defining Roadside Objectives
    • 7.2.3 Evaluating Treatment Options
    • 7.2.4 Establishing a Vegetation Treatment Plan
    • 7.2.5 Monitoring Treatments
  • 7.3 Vegetation Treatment Options
    • 7.3.1 No Action
    • 7.3.2 Mowing
    • 7.3.3 Manual Removal
    • 7.3.4 Herbicides
    • 7.3.5 Grazing
    • 7.3.6 Fire
    • 7.3.7 Biological Control
    • 7.3.8 Mechanical Removal
    • 7.3.9 Haying
  • 7.4 Prevention
    • 7.4.1 Maintaining a Weed-Resistant Roadside Environment
    • 7.4.2 Treating Disturbances for Quick Recovery
  • 7.5 Protection
• Chapter 8: Case Studies
• References

7.1 INTRODUCTION

For the Designer
To ensure that revegetation objectives are carried through during the maintenance phase, maintenance staff can be informed of these objectives and how they relate to maintenance activities.

Roadside maintenance is the final step in the revegetation timeline. It occurs when the revegetation efforts and responsibilities are transferred to the road maintenance staff for the long-term management of roadside vegetation. If the transfer is successful, revegetation objectives are carried out for many years with good results. The intended audience for this chapter is maintenance staff. In handing off a roadside revegetation project, it is helpful if the objectives and reasoning behind the revegetation plan are understood by maintenance staff. This may have occurred if maintenance staff were included during the planning phases of the revegetation plan. In such instances, maintenance staff can provide insights into the development of a vegetation management strategy (Section 3.2) and bring to the discussion a thorough understanding of how vegetation responds to various management activities specific to the project environment.

Many state DOTs have a statewide Integrated Vegetation Management (IVM) plan or an Integrated Roadside Vegetation Management (IRVM) plan. Some states have more detailed IVM plans for regions within the state. IVM plans are typically updated annually based on monitoring of the previous year’s work.

Figure 7-1 | Components of a decision-making process for treating unwanted vegetation

The IRVM is “an approach to right-of-way maintenance that combines an array of management techniques with sound ecological principles to establish and maintain safe, healthy and functional roadsides” (Brant et al 2015). It applies many of the Integrated Pest Management concepts developed for agriculture, horticulture, and forestry to roadside vegetation management. IVM plans typically include sections on preventing the introduction of unwanted vegetation, protecting rare plants, preserving natural areas, and developing a decision-making process for treating vegetation.

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7.2 DECISION PROCESS FOR TREATING UNWANTED VEGETATION

Most states have a decision-making process within the IVM for treating unwanted vegetation. The process includes some or all the steps outlined in Figure 7-1. An IVM decision-making process can be used to evaluate the control of an individual target weed species (e.g., noxious weed control) or control the vegetation on an entire section of roadside. In this process, roadsides are inventoried and objectives are set for unwanted vegetation. All methods for treating unwanted vegetation are considered, including no action, mowing, herbicide application, manual removal, prescribed burns, grazing, and biological control. A treatment plan is developed based on a thorough understanding of a species or plant community. Treatment plans often outline the “action threshold” or “tolerance level” that, when exceeded, constitutes the implementation of a vegetation treatment. The effectiveness of the treatment is determined based on monitoring. If the treatment is ineffective, then the treatment options are reviewed and updated, if appropriate. If the treatments are effective, then no action is taken and monitoring continues.

7.2.1 INVENTORY OF ROADSIDES 

Roadsides are inventoried for weeds or unwanted vegetation. For some states, invasive and noxious weeds are reported using GPS equipment and GIS mapping technology. The associated maps often prioritize sections of road that require some form of vegetation control. Roadside inventories can also show areas of desirable vegetation, rare plants, threatened species or populations, natural areas, pollinator habitat, and vegetative types. Vegetation assessments conducted during the planning stages of a revegetation plan may be useful in inventorying roadside vegetation by identifying target weed species and prioritizing roadsides for treatment (Section 3.6.1).

7.2.2 DEFINING ROADSIDE OBJECTIVES 

The backbone of a treatment plan is composed of clearly stated road maintenance objectives. These include objectives for road safety as well as roadside resources. Objectives are set at a statewide level in the IVM plan or at the local or regional level within a state.

Many states assign maintenance objectives to roadside zones similar to those shown in Figure 3-8. Oregon and Washington, for example, identify three roadside zones (WSDOT 2016, Oregon DOT 2013):

• Zone 1—This zone borders the roadway pavement with vegetative objectives of preventing pavement breakup, preventing noxious weeds, facilitating a “soft return” to the travel lane should a driver accidentally veer, and maintaining maximum visibility.
• Zone 2—This zone is spatially located between zone 1 and zone 3, and the vegetative objectives are to maintain low growing vegetation for maximum sight distance, enhance visual qualities, and maintain hydraulically functioning ditches. Pollinator habitat can also be an objective.
• Zone 3—This zone is farthest from the roadway and has fewer restrictions for maintaining low-growing vegetation for sight distance. These areas may contain shrubs and trees, and can serve as pollinator habitat.

Each of these zones is treated differently and may have separate action thresholds, treatment plans, monitoring activities, and maintenance schedules.

Roadside objectives are also developed for the important resources associated with roadsides. These resources include pollinator habitat, water, natural areas, and visual resources. These objectives are brought forth from the prevention and protection portions of the plan (Section 7.3 and Section 7.4) of the IVM. It is important that resources, safety, and road maintenance objectives are clearly stated so that treatment options can be developed accordingly.

It is important to note that state departments of transportation manage areas that are not roadway or right-of-way. These areas include rest areas, “back 40” property, stockpile lots, maintenance yards, office grounds, bike paths, scenic viewpoints, and points of interest pull- outs. Management objectives for these areas may integrate well with creating or improving pollinator habitats because alternative uses are unlikely to conflict with maintenance activities or expose people (maintenance staff or volunteers) to the dangers of the roadside.

7.2.3 EVALUATING TREATMENT OPTIONS

In this step of the decision-making process, all possible treatments are evaluated for how each best meets the road objectives. The details of each vegetation treatment are described in Section 7.3. In evaluating each treatment, it is important to consider how well each treatment meets the roadside safety, maintenance, and resource objectives. If there are conflicts, how can the treatment be modified?

To evaluate treatments, it is helpful to have a working knowledge of the target weed species or plant community of concern. It is also helpful to understand how a weed species or an entire plant community changes over time through succession, how they respond to various disturbances, how they can be controlled or maintained, and how treatments change the direction and rate of plant succession (Figure 3-9). Some of this information can be obtained from the vegetation management strategy outlined in the revegetation plan or from the designers of the revegetation plan (Section 3.2). Adjacent maintenance departments, land owners, and local agricultural extension specialists are good contacts to discuss the best controls for the target weed species present on the project site. Plant Guides located on the profile page of the USDA PLANTS database provide control treatments for many weed species. Other resources include a publication by Harper-Lore et al (2013) that describes how to control 40 common weed species in the United States.

In evaluating treatments, it is also important to understand how each treatment affects roadside resources. Pollinators are affected by most vegetation treatment methods, and a knowledge of the important pollinators on the roadsides, their life history, and their habitat requirements can help in developing the appropriate treatments. Water quality can be affected by vegetation maintenance, especially where bare soil is created near drainages and stream courses. Reviewing the Storm Water Pollution Prevention Plan for the project area or road corridor, if it is available, can help the designer identify appropriate treatments.

7.2.4 ESTABLISHING A VEGETATION TREATMENT PLAN

The vegetation treatment plan prioritizes the treatments that best meet the road objectives. It addresses the action threshold for treatment implementation to control a target weed species or a plant community on a section of roadside. The action thresholds may be based on the phenological condition of the vegetation (e.g., treat when average grass height is 2 feet), presences of a noxious weed (e.g., control all noxious weeds no later than flowering stage), and safety threat (e.g., trim or remove trees when they are considered hazardous to road or neighboring property). When the action threshold is exceeded, the plan details the treatment that will be used (e.g., timing, rates, equipment, personnel).

The treatment plan prioritizes the areas to be treated and sets site limitations (e.g., distance from streams or bodies of water, slope steepness, saturated soils). It also addresses the effects of the treatment on other roadside resources and options for mitigating negative effects. For example, the effects of mowing on pollinators and pollinator habitat can be minimized if mowing is done outside the flowering period of most forb species.

7.2.5 MONITORING TREATMENTS

The treatment plan outlines how roadsides will be monitored. Setting up monitoring for operations and maintenance is similar to the steps outlined for vegetation monitoring (Section 6.2). Monitoring in an IVM plan addresses the following:

• Purpose—Determines if the action threshold was exceeded, treatments were applied as prescribed, treatments were effective, or other resources were negatively affected
• Who—Identifies personnel or expertise needed
• What—Determines what is being monitored (e.g., noxious weed presence, vegetation height)
• When—Defines frequency and time of year
• Where—Delineates sections of road to be monitored
• How—Determines intensity and methodology
• Logistics—Timeline, budget, and equipment

Monitoring is the feedback loop for effectively controlling unwanted vegetation over time. As outlined in Figure 7-1, monitoring is conducted to determine if an “action threshold” is exceeded. If it is not, then monitoring continues as scheduled and no treatments are made.

If an action threshold is exceeded, then a treatment is applied according to the treatment plan. Implementation monitoring during treatment application records whether the treatment was applied as prescribed or if changes were made based on equipment or site factors. Post-treatment monitoring evaluates the effectiveness of the treatment and whether the treatment affected other resources (e.g., pollinator, water quality, visual resources). If the treatment was not effective in controlling unwanted vegetation or other resources were adversely affected, then a reevaluation of the treatment is usually made and, if necessary, the treatment plan can be changed.

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7.3 VEGETATION TREATMENT OPTIONS

When developing a vegetation treatment plan, it is important that the target vegetation and the objectives outlined in the IRVM plan are understood. It is also important to understand the resources of value that may be affected with a vegetation treatment. These include water quality, wildlife habitat, visual resources, and pollinators. This section describes common vegetation treatments and how they affect these resources, with an emphasis on enhancing pollinators and pollinator habitat.

Because pollinator species can be strongly affected by weed control treatments, it is helpful to know the important pollinator species that inhabit the area during maintenance activities and develop weed treatments that minimize the negative effects on their populations and habitat. This section outlines vegetation management practices that can control target vegetation while supporting pollinators. Additional details are provided in two recent publications from the U.S. Department of Transportation (Hopwood et al 2015, Hopwood et al 2016), which review the best management practices (BMPs) for controlling roadside vegetation while optimizing pollinator habitat and reducing pollinator mortality. In addition, a review of Section 3.11.6, which covers control of unwanted vegetation before and during construction, may be useful.

Given the complexity of developing treatments that control target vegetation while maintaining or improving pollinator habitat, some general pollinator strategies may aid in designing vegetation treatments specific to a project environment. These are outlined in Figure 7-2.

7.3.1 NO ACTION

While not taking an action to control vegetation is not a treatment, it is included in this section as a reminder that there are times when vegetation does not need to be treated. Reviewing vegetation management objectives in the IRVM plan, especially how treatments may affect resource objectives such as water quality and pollinator health, may provide justification for the “no action” treatment. On roadsides where rare plant species or at-risk pollinator species are present, taking no-action may be the most prudent approach to protecting species.

7.3.2 MOWING

Mowing is frequently used to maintain roadside vegetation by reducing invasive weeds and woody plants, improving driver sight lines, allowing vehicle pull off, and reducing the risk of wildfires. Typically, vegetation in the clear zone, a band of vegetation directly adjacent to the pavement or shoulder, is mowed regularly to keep the vegetation short for drivers who need to regain control of their vehicle and to lower the fuel level for spread of fires. Periodic mowing within the clear zone creates a habitat that is not typically used by pollinators. However, roadside vegetation beyond the clear zone can support pollinators.

Mowing at certain times can directly kill pollinator eggs or larvae present on the vegetation. It can also indirectly affect adult pollinators by temporarily removing host and flowering plants (e.g., food sources). For these reasons, it is important to carefully time or limit mowing during the growing season. This is especially true if the habitat supports endangered or rare and sensitive pollinator species. Higher mowing frequencies reduce native plant growth, plant diversity (Parr and Way 1988), and the ability of forbs to compete with grasses (Williams et al. 2007), and decrease the amount of nectar and pollen present on the roadside. More frequent mowing can also increase the roadkill of pollinators, especially butterflies (Skorka et al 2013). Therefore, minimizing the number of times a roadside is mowed benefits many pollinator species.

Reducing routine mowing of the entire right-of-way (fence to fence) benefits pollinators by allowing wildflowers to bloom and thereby supply nectar and pollen as food. It is best to restrict routine mowing to the clear zone as much as possible, and mow beyond the clear zone only when there are well-defined objectives, such as reducing brush or maintaining lines of sight. Reducing mowing beyond the clear zone to two or fewer times a growing season is best for wildflowers and pollinators. In some regions, mowing can be reduced to once a year per site, every other year, or even every two to three years, depending on the regional intervals of mowing needed to control woody plant encroachment or to reinvigorate populations of wildflowers.

When timed appropriately, mowing can reduce the effects on pollinators and promote plant diversity. It is optimal to delay mowing until autumn or after the first frost if regional constraints allow. When mowing is delayed, butterflies and other pollinators with larvae that reside on vegetation are able to complete their full life cycles, and flowering plants are able to bloom and provide pollen and nectar to pollinators uninterrupted throughout the growing season. If mowing must occur during the growing season, consider selecting a time to mow that balances vegetation management needs (e.g., noxious weed control) with the resource needs of pollinators (e.g., presence of flowers and host plants). For example, mowing at a time that promotes the growth of wildflowers benefits pollinators in the long term. Timing will vary with region. Wildflower growth is promoted by a mid-summer mow in some regions, while in others mowing after spring bloom might be optimal. It is also worth considering varying the season when mowing occurs every few years to increase plant diversity. Mowing consistently at the same time every year will select some plants over others. Plant diversity can be maintained by occasionally varying the timing of mowing, which will favor different plants and prevent certain plants from dominating.

It is important to time mowing to avoid vulnerable stages of the life cycle of any rare or declining species that are present. For example, in Texas, to reduce harm to monarch butterflies, it is best to avoid mowing before March and between May and August, time periods during which monarchs are breeding in the region. Finally, it is helpful to adjust the height of the mower. By mowing vegetation at a height of 12 to 16 inches, vegetation recovers more quickly and plant stress is reduced, particularly during dry periods or drought. Mowing also leaves a greater depth of vegetation for pollinators to use.

There may be a public perception that by reducing mowing, road departments are not taking care of roadsides, which can be an obstacle to implementing mowing strategies that benefit pollinators. Public education may change this perception with time as the public becomes more aware of the benefits of roadsides to pollinator populations and health.

7.3.3 MANUAL REMOVAL

Hand-pulling weeds can be the most complete method of controlling specific weeds because it is highly targeted. Hand-weeding is well suited for removal of weeds that occur in low numbers or that are scattered throughout a site. Hand-weeding is often the least intrusive method of removing weedy species as it has the least effect on pollinators.

Tools that help with hand-weeding include hoes, picks or pulaski axes, trowels, and shovels. Tree and weed puller tools are designed to provide grip and leverage for removing deep-rooted species such as scotch broom. It is important to target weeds during their active growth stages before the weeds have flowered and set seed. For perennial and rhizomatous species, it is best to remove as much of the root material as possible because many plants can re-sprout from root fragments.

One strategy for hand-pulling is the Bradley Method (Brock 2016) which prioritizes the areas to be weeded, beginning in undisturbed areas first, and then working out toward more heavily infested areas. When pulling weeds by hand or with tools, it is useful to minimize soil disturbance so that weeds do not become established. It is also important to dispose of weeds in designated areas. If weed removal results in large patches of bare soil, re-colonization by unwanted species can be reduced by seeding with desirable species.

7.3.4 HERBICIDES

Herbicides are used to control woody vegetation as well as target weed species on roadsides. The use of herbicides can benefit pollinators by suppressing undesirable plants and encouraging the valuable native plants that provide them with food or shelter. However, used indiscriminately, herbicides can reduce the quality of roadside habitat by removing floral resources and host plants, and may be directly toxic to some pollinators (Mader et al 2010; Russell and Schultz 2010; LaBar and Schultz 2012). Overuse of herbicides can also weaken stands of vegetation, making them more vulnerable to weed invasions, which also indirectly affect pollinators (Inset 7-1). By using herbicides as efficiently as possible, maintenance staff can reduce both the amount applied and the effect on plants that benefit pollinators. Using products selectively, timing applications carefully, and following label directions can increase the effectiveness of herbicide use and decrease impacts to pollinators and other resources.

It is important to use the appropriate products and application rates that are effective in controlling the target weed species yet have minimal effects on non-target plant species. Whenever possible, the use of selective herbicides—those formulated to control specific weeds or groups of weeds—can reduce damage to nontarget plants. Nonselective herbicides—those that are broad-spectrum and kill or damage all plants—can also be used selectively to reduce effects on nontarget plants. For example, nonselective herbicides can be used selectively by applying them on weeds when desirable native plants are dormant and by using directed or targeted applications (e.g., spot spraying). In addition, understanding how quickly the herbicide being applied degrades on the site ensures that seed germination and restoration planting are not negatively affected. Herbicide labels include information about selectivity and persistence.

Applications can be timed to be most effective based on the herbicide’s mode of action and the application technique. For example, when using a systemic herbicide (absorbed by the plant and transported throughout the plant by the vascular system), perennial weeds can be treated in late summer and fall. During this period, perennials begin to move sugars down to their roots, and the herbicide is translocated to vegetative reproductive structures where it is most effective at controlling the plant. Applications of herbicides at the stage of growth when the weed is most vulnerable can make applications most successful. For many weeds, this is the seedling or rosette stage.

Reducing off-site movement of herbicides and the use of nonselective broadcast applications can help avoid damage to non-target plants that provide pollinators with food or shelter. Referring to road inventories of unwanted vegetation (Section 7.2.1), conducting training in weed identification, and using plant identification reference materials to recognize noxious and invasive weeds will help distinguish these species from similar non-target species. In order to avoid weakening non-target species, weeds can be targeted using spot treatment applications made with a backpack sprayer, weed wiper, or similarly appropriate technology. Using highly targeted applications on cut stems, stumps, or under bark can also reduce unnecessary effects to desirable plants. Broadcast treatments or pellet dispersal are recommended only for dense infestations of weeds or for clear zone or guardrail treatments.

The off-site movement of herbicides can be reduced by selecting appropriate spray equipment, periodically calibrating equipment, and adhering to the pesticide label. Nozzles that produce larger droplets are less likely to cause herbicides to drift off target. Equipment that is calibrated regularly limits over and under applications. It is best to avoid applications when wind speeds are greater than 15 mph and during a temperature inversion (when warmer air above traps cooler air near the ground) when herbicides and other pesticides can linger in the air and move long distances offsite with air movement.

To reduce direct contact exposure to pollinators, herbicides can be applied during a time of day when pollinators are less active. Many pollinators (but not all) are less active before the sun rises or after the sun sets, and are also less active at cooler temperatures (below 50 degrees Fahrenheit). Additionally, avoiding broadcast applications of systemic herbicides and herbicides with long residuals reduces exposure to butterfly and moth caterpillars that can be poisoned by consuming contaminated vegetation.

7.3.5 GRAZING

Grazing is used to limit tree and shrub invasion, provide structural diversity, and encourage the growth of nectar-rich plants. However, livestock grazing is only beneficial to plant diversity, and in turn, pollinators, at low to moderate levels during short periods of time separated   by long recovery periods (Hopwood et al 2016). Grazing can negatively affect insect communities by changing the plant community structure and diversity (Kruess and Tscharntke 2002). Insufficient forage from grazing can decrease bumble bee populations (Carell 2002; Hatfield and LeBuhn 2007) and destroy potential nest sites through trampling (Sugden 1985). Intensive grazing can also affect butterfly populations through trampling (Warren 1993) and altering plant community composition (Stoner and Joern 2004).

Development of a grazing plan that includes careful consideration of the type of grazer, its food preference, and how well the grazer can be managed is important for managing invasive species and compatibility with pollinator health and other resources. For example, goats and sheep can be controlled through herding when they are brought onto a site and when they are removed, bracketing periods of time when pollinators and pollinator habitat are least affected. Goats and sheep preferentially eat broadleaf plants and are therefore the preferred grazers for sites where broadleaf weeds are an issue. At specific densities and duration, goats and sheep can control large infestations of invasive weeds. In addition, they can be controlled in areas near water, thereby reducing effects on water quality, and can be effective in inaccessible spots, such as steep slopes.

It is best to introduce grazers at a time when they preferentially feed on the target weed species. Grazing is most effective, for example, when target weeds are palatable; however, this period may be detrimental to pollinators. If rare or imperiled pollinators are present, timing grazing so as to avoid breeding and foraging periods is best. Avoiding grazing during the adult flight period or when imperiled butterfly or moth larvae are feeding on host plants reduces the effect on pollinators. It is also important to avoid grazing during periods when floral resources are already scarce, as grazing during such times can eliminate pollinators from sites over time. Lastly, the stocking density of grazers can help to determine the duration   of grazing. If stocking density is high, it is best to keep the duration relatively short so that desirable vegetation is not affected.

7.3.6 FIRE

Prescribed fire is used to manage roadside vegetation and rejuvenate plant diversity in some regions of the United States that have a history of natural fires. Prescribed fire can benefit pollinators through restoration or maintenance of suitable habitat (e.g., Huntzinger 2003), but it can also be harmful when not applied appropriately and have long-term effects on the populations of some species (e.g., Ne’eman et al 2000). For example, burns during the growing season destroy eggs, caterpillars, and above-ground nests and remove vegetation at a time when pollinators need floral resources, host plants, and nesting materials, while winter burns destroy species that overwinter in leaf litter or stems. The scale of the prescribed fire can also affect pollinators. For example, an extremely large and expansive fire may kill pollinators overwintering in above-ground biomass, and such fires during the growing season may eliminate all floral resources in a given area. Smaller, dispersed fires, on the other hand, conserve floral resources and support pollinators in the area by providing refuges.

Burns that are timed so as to have the least effect on pollinators and limiting the scale and frequency of each burn are important pollinator-friendly practices. It is best to use prescribed burning on sections of the roadside corridor rather than the entire corridor. By leaving unburned roadside habitat, enough pollinators remain to recolonize the burned areas. Rotational burning, such as burns conducted three to five or more years apart, allow time for pollinator populations to recover. Rotational burning can provide the benefits of prescribed fire without irreparably damaging the local pollinator community (Black et al 2011). Varying the timing of prescribed burns can also reduce harm to pollinators by avoiding continuously affecting certain pollinators and components of the roadside plant community. Burns affect pollinators no matter when the burn occurs, so altering the timing of burns can reduce negative effects to a particular group or suite of pollinators.

7.3.7 BIOLOGICAL CONTROL

Biological control is the process of introducing natural enemies of the target weed that occur in the geographic region of the weed. Although biological weed control is not currently widely implemented by state departments of transportation, several have released natural enemies to such weeds as purple loosestrife (Lythrum salicaria), leafy spurge (Euphorbia esula) (Johnson 2000), yellow star thistle (Centaurea solstitialis), and Russian thistle (Salsola kali) (Harper-Lore et al 2013). Biological control can be an effective and focused approach to weed control. However, there are ecological and economic risks associated with introducing a species outside of its natural range, including unpredictable and irreversible consequences (Simberloff and Stiling 1996). The Eurasian weevil (Rhinocyllus conicus), for example, was introduced to control musk thistle (Carduus nutans), but expanded its host plants to include native thistles after introduction, including several rare thistle species (Louda et al. 1997). The loss of native thistles or other native species affects the wildlife that depend upon the plants, including pollinators that visit the plants for pollen and nectar or use the plants as hosts for their caterpillars.

It is best to avoid using natural enemies that have expanded their hosts to include native plants. Coordinating with state agencies, keeping records about locations of releases, and monitoring the target weed populations and potential non-target native species can be used to evaluate the potential impacts of biocontrol agents.

7.3.8 MECHANICAL REMOVAL

Weed populations can be opportunistically removed during road construction. Removal of populations is accomplished by excavating soils within the populations at least a foot deep and transporting the weed-contaminated material offsite to an approved storage area.

Brush may also be removed from roadsides. Brush removal can benefit pollinator health when brush and trees that pose no risk to motorists are left on site and by opening up the canopy along forest edges. Mechanical trimming to remove problematic shrubs or trees and selective trimming to partially remove woody vegetation can benefit pollinators by creating opportunities for wildflowers to grow. However, complete removal of trees and shrubs is not always beneficial because many butterflies and moths use woody native plants as hosts and to roost during the flight period, and some tunnel-nesting bees use the stems of some shrubs as nesting sites.

Removal of any brush or trees that could be hazardous to motorists is important. This includes plants that could impede sight distance, become dangerous fixed objects, fall onto the highway, or shade the road in winter creating patches of ice. When possible, consider leaving snags or trees with cavities in areas where they are set back from the road and pose no safety risk. Snags can provide nesting habitat for some bees, as well as habitat for birds and bats.

Transitional areas between forest and grass can be created by using brush removal to feather or soften forest edges adjacent to clear zones. Edge feathering involves thinning portions of the forest canopy along the edge next to grassy areas and removing undesirable or unhealthy trees. Periodic cutting to maintain healthy growth and an open canopy benefits remnant patches of savanna, forest, or other habitat dominated by woody vegetation, improves the quality of the habitat for pollinators and many birds, and is aesthetically pleasing.

7.3.9 HAYING

In some states, landowners are permitted to cut and remove roadside vegetation for animal fodder. States might grant emergency hay permits under drought conditions, for example, or allow annual haying by adjacent landowners on certain roads throughout the growing season. Haying is not a tool typically used by roadside maintenance staff, although it does affect roadside vegetation and thus pollinators by the abrupt removal of flowers and host plants from a site. In general, haying once in the middle of the growing season can favor wildflowers and cool-season grasses that are often suppressed by dominant warm-season grasses. However, too-frequent haying in a growing season can reduce roadside revegetation over time (Jacobsen et al. 1990), thereby reducing floral resources for pollinators. A poorly timed haying may have severe consequences for rare or endemic pollinator species. When possible, maintenance staff who communicate with landowners can suggest they hay a portion of the entire site at a time, leaving a refuge for pollinators. Additionally, setting the mower blades at 12 to 16 inches reduces the effect on vegetation structure that provides nesting and overwintering habitat, and allows vegetation to recover and bloom more quickly.

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7.4 PREVENTION

Ideally, when maintenance staff takes over a roadside revegetation project, the site is weed-resistant (Section 3.11.4). Maintaining a healthy native plant community thereafter greatly reduces the possibility for future weed invasion. The role of maintenance then, is to prevent or minimize unwanted vegetation from becoming established in a weed-free revegetation project. Prevention is the first line of defense in vegetation management and it is accomplished by maintaining a weed-resistant roadside environment, quickly treating disturbances, and protecting natural areas.

7.4.1 MAINTAINING A WEED-RESISTANT ROADSIDE ENVIRONMENT

Roadside vegetation changes over time through successional processes and land uses. If the revegetation project is implemented successfully, the roadside vegetation should continue to be weed-resistant. That can change, however, if the vegetation is disturbed, creating bare soil where weeds can become established. Some practices to maintain a weed-resistant roadside environment are described below.

Minimizing Ground Disturbance
Maintaining a roadside free of ground disturbance is not always possible, but minimizing the amount of disturbance can reduce the area affected. Ground disturbances, and potential solutions, include the following:

• Rutting from vehicle run-offs (repairing roadsides soon after crashes)
• Mowing slopes that exceed 3(H):1(V) often cause rutting and erosion from equipment
• Mowing when soils are too wet, compacting vegetation and soil, and causing erosion
• Landslides (maintaining stable cut and fill slopes)
• Gullies and rills from road runoff (improving road drainage, soil structure, and groundcover)
• Ditch cleaning (limiting ditch cleaning or maintaining a groundcover with occasional mowing)
• Unauthorized trails and off-road vehicle disturbances (controlling access)
• Grazing (controlling animals)
• Vegetation maintenance (performing maintenance activities to prevent soil exposure)

Disposal of Soil in Designated Areas

Road maintenance often necessitates the disposal of soil that comes from maintaining the road. Material from landslides, ditch cleaning, and winter gravelling operations is sometimes pushed over the roadsides or deposited in areas along the roadside, potentially covering roadside vegetation with exposed soils. It is important that excavated soils be removed and deposited in designated areas that have been reviewed for their offsite effects on water quality and other resources.

Controlling Noxious Weeds

If there are no sources of weed seeds, then exposed soils revegetate from the seeds that are sown by the maintenance staff. It is important to reduce or eliminate unwanted seed sources by controlling noxious weeds prior to disturbances (Section 7.3).

Retaining Shade

Many weeds require full or partial sunlight to thrive (Penny and Neal 2003); therefore, retaining shade from existing native vegetation is one strategy to control some weed species. Cutting trees and shrubs or mowing vegetation can increase light and space for invasive weeds (Schooler et al 2010).

Mulching of Woody Material On Site

Maintenance activities that produce material from processed slash or excess vegetation from right-of-way clearing can be shredded and spread over the roadsides as mulch, especially on areas that have bare soils. Strategic placement of this material can reduce the potential for weed establishment.

7.4.2 TREATING DISTURBANCES FOR QUICK RECOVERY

When ground disturbances do occur, a quick response by maintenance staff to treat these areas can ensure that unwanted vegetation does not become established, as described below.

Limiting or Controlling the Activity Causing the Disturbance

The first response is to assess the activity that caused the disturbance and to fix it before proceeding to revegetate the site. For example, if runoff from a road surface causes erosion on a fill slope, then it is important to fix the drainage before restoring the vegetation. If a large vehicle run-off creates rutting of the roadside, it is recommended that soil filling and regrading of the area occur prior to reseeding. If off-road vehicle use creates bare soil, then access to the area would be limited prior to revegetating the site.

Having an Appropriate Seed Mix Readily Available

Having an appropriate seed mix available prior to a disturbance is important because locating the appropriate seed mixes at the quantities needed can be difficult on short notice. Seed mixes may be available commercially or from the designer of the revegetation project. At a minimum, a list of appropriate plant species in a seed mix can be obtained from the revegetation plan or using the ERA tool. If a seed mix is maintained for these disturbances, keeping the mix in favorable long-term storage environments maintains its viability (Section 5.3.4, see Seed Storage). The disturbance may need to be stabilized until it is favorable to seed (Section 3.8.6).

Improving Soils

Sites that have been disturbed often have poor soils because the topsoil has been removed or mixed with the subsoil (e.g., landslide scars, gullies). Compost blankets are a quick way of covering bare soils and increasing the soil productivity at the same time (Section 5.2.3, see Seed Covering).

Oversowing Seeds

For the Designer
Seeding at excessive rates can benefit the project to a point. Understanding conditions that contribute to, or limit, seed establishment will help determine maximum seeding rates.

On disturbed sites, environmental conditions for seed germination are often poor for many native grass and forb species. Applying seeds at excessive rates increases the probability of greater plant establishment. It is important to understand the site’s environmental conditions that facilitate seed germination and establishment, as all sites have a maximum seed load they are able to support. If seeding is conducted above this rate, a net gain may not be realized.

Applying a Weed-free Mulch

After seeds are sown on a disturbed area, applying a mulch over the seeds ensures that soil erosion is kept to a minimum and seeds have a favorable germination environment. Most seeds can germinate through mulches applied ½ to 1 inch thick on top of the seed. A variety of mulches are available that include wood fiber, hydromulch, straw, hay, erosion mats, and manufactured wood strands (Section 5.2.3). It is important to obtain weed-free mulches so the introduction of unwanted vegetation is kept to a minimum. Having weed-free sources available prior to disturbances expedites a quick recovery.

Using Clean Equipment

Inspecting and cleaning vehicles and equipment that will apply seeds and mulch ensures that unwanted vegetation is not brought onto the site. The equipment is typically pre-washed by the contractor at an approved off-site facility. Washing with high-powered, high-temperature water (steam cleaning) is effective. After cleaning, equipment can be inspected at the wash site or another agreed upon location prior to arriving at the project site. Overlooked areas to inspect are the hoppers and hoses of hydroseeding equipment.

Avoiding Nitrogen Fertilizer the First Year

Consider applying a slow-release fertilizer (instead of fast-release fertilizers) after native plants have established to reduce the nitrogen levels available for annual weed establishment (Section 3.11.4).

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7.5 PROTECTION

Roadsides may contain unique plant communities and rare plants that may need protection. These areas are identified in the planning process but are managed during the operations and maintenance phase of the project. Many states have programs to protect listed species, species of interest, or remnant plant communities (AASHTO 2013a) on roadsides. They are called by a variety of names, including Special Management Areas (SMAs), natural heritage remnants, wildflower research areas, and Biological Management Areas (BMAs). These areas have some or all of the following features in common (adapted from AASHTO 2013a):

• Collaboration—Most states with established management areas in right-of-way have accomplished this through collaboration with maintenance staff; conservation groups; and federal, state, and local agencies.
• GIS—Many states use GIS to identify rare plant populations and remnant habitats. Known locations of rare species are obtained from state departments of natural resources, the U.S. Fish and Wildlife Service, the U.S. Forest Service, the Bureau of Land Management, counties, local environmental groups, and individuals.
• Management plans and BMPs—Most special management areas have plans or BMPs for how to preserve remnant sites or species of interest. These practices include how vegetation control treatments, such as mowing, herbicides, prescribed burns, and grazing, will be used to preserve and enhance remnant areas or species of interest. Maintenance treatments that support species of interest, such as minimizing shading from trees or competition from surrounding vegetation, can be a part of the BMPs. In areas where species of interest require full sunlight for survival, trees and shrubs around these plants may be removed. Where competing vegetation or noxious plant species threaten species of interest, herbicide may be applied or manual removal of vegetation around these species may occur. In areas where potential soil erosion and landsides threaten species of interest or remnant areas, soil stabilization measures may be taken. Public access may be curtailed if it affects plant survival.
• Signage—Some states place special signs along the boundaries of the management areas and have instructions on the signs indicating what maintenance activities are allowed.
• Training—Some states have developed training programs for maintenance staff specific to managing rare species. This training covers the identification of species of interest, habitat, and preferred management options.

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