Pollinators and Roadsides: Best Management Practices for
Managers and Decision Makers

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January 2016

Cover Photo
Courtesy: Xerces Society for Invertebrate Conservation
Photographer: John Anderson, Hedgerow Farms, Inc.
State: California
Description: Showy milkweed (Asclepias speciosa) with monarch butterfly (Danaus plexippus), honey bee (Apis mellifera), and leafcutter bee (Megachile spp.). Milkweeds are the required host plants for monarch caterpillars and support a broad diversity of pollinators with their nectar.

Technical Report Documentation Page

1. Report No. FHWA-HEP-16-020	2. Government Accession No.	3. Recipient’s Catalog No.
4. Title and Subtitle Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers		5. Report Date December 2015
		6. Performing Organization Code
7. Author(s) Jennifer Hopwood, Scott Black, and Scott Fleury		8. Performing Organization Report No.
9. Performing Organization Name and Address ICF International ICF Incorporated, L.L.C. 9300 Lee Highway Xerces Society for Invertebrate Conservation 628 NE Broadway, Suite 200 Portland, OR 97232		10. Work Unit No. (TRAIS)
		11. Contract or Grant No. DTFH61-11-00033/TO 5001
12. Sponsoring Agency Name and Address Federal Highway Administration 1200 New Jersey Ave SE Washington, DC 20590		13. Type of Report and Period Covered Best Management Practices 2015
		14. Sponsoring Agency Code HEPE-1
15. Supplementary Notes Contracting Officer’s Representative: Deirdre Remley, FHWA, HEPE-20, 202-366-0524, deirdre.remley@dot.gov
16. Abstract Pollinators are critical to our food supply as well as to the health of ecosystems. Wild pollinators such as the monarch butterfly and a number of bumble bee species are in decline, and beekeepers in the United States and Europe have reported significant losses of managed European honey bee colonies. Pollinator declines are attributed to loss of habitat, pesticide exposure, diseases, parasites, and effects of introduced species. Roadsides can benefit pollinators by providing foraging habitat, places to breed, nest, and overwinter, and may act as corridors, linking patches of fragmented habitat. These best management practices identify key steps that State Departments of Transportation (DOTs) can take to improve the quality of roadside habitat for pollinators including 1) adjusting roadside vegetation management techniques to accommodate pollinator resource needs, and 2) enhancing and restoring native roadside vegetation to include plant materials that improve pollinator habitat.
17. Key Words pollinators, integrated vegetation management, butterflies, bees, bats, moths, nectar, host plants, roadside habitat, reduced mowing, native plants, roadside landscape design, roadside maintenance		18. Distribution Statement No restriction. This document is available to the public from the sponsoring agency at the website https://www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators.aspx.
19. Security Classif. (of this report) Unclassified	20. Security Classif. (of this page) Unclassified	21. No. of Pages	22. Price

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Pollinators and Roadsides: Best Management Practices for Managers and Decision Makers

Contents

List of Tables and Figures

Acronyms and Abbreviations

Photo Credits

Chapter 1 - Summary

Chapter 2 - Introduction
Report Context
Report Development
Report Organization

Chapter 3 - A Primer on Pollinators and Pollinator Use of Roadside Habitat
Importance of Pollinators
Pollinator Biology
Pollinator Decline
Roadsides and Pollinator Conservation

Chapter 4 - Roadside Vegetation Management and Pollinators
Overview
Roadside Vegetation Inventories
Remnant Habitat
Invasive and Noxious Weeds
Priorities for Future Restorations
Pollinators and Integrated Roadside Vegetation Management
Mowing Recommendations
Herbicide Recommendations
Alternative Vegetation Control Methods
Management for State-Listed, Federally-Listed, Rare, Endemic, and/or Sensitive and Declining Species of Pollinators
Summary of Recommendations for Adjusting Roadside Vegetation Management to Benefit Pollinators

Chapter 5 - Using Native Plants to Restore Roadsides for Pollinators
Overview
Value of Native Plants in Roadside Plantings
Using Native Plants in Roadside Plantings to Benefit Pollinators
Plant Diversity and Density
Plant Selection
Sourcing Native Plant Material
Compatibility with Highway Safety
Prioritizing New Plantings for Pollinators
Summary of Recommendations for Using Native Plants in Roadsides to Benefit Pollinators

Chapter 6 - Overcoming Obstacles to Implementing Pollinator-Friendly Practices
Reducing Mowing
Reducing Herbicide Use
Conducting Roadside Vegetation Surveys
Using Alternative Vegetation Management Tools
Obtaining Plant Materials
Training Staff
Value of Native Plants
Plant Establishment and Management
Native Plants, Education, and Public Relations
Raising Public Awareness
Staff Awareness
Resolving Complaints
Final Thoughts

Chapter 7 - Resources for Roadside Management for Pollinators
Vegetation Management
Native Plants and Restoration
Pollinators and Roadsides
Pollinator Plant Resources
Pollinator Biology and Conservation

Chapter 8 - Contributors

Chapter 9 - References Cited

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Tables and Figures

Tables

3-1 Pollinator Habitat Needs
5-1 Examples of Native Plant Species Suitable for Use in Roadside Revegetation and Examples of the Ecosystem Services they Provide

Figures

4-1 Regional Recommendations for Times to Mow Based on the Timing of the Monarch Butterfly Lifecycle
5-1 Root Systems of Native Plants

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Acronyms

ADOT	Arizona DOT
DNR	Department of Natural Resources
DOTs	Departments of Transportation
ESA	Endangered Species Act
FHWA	Federal Highway Administration
GIS	Geographic information systems
GPS	Global positioning systems
IRVM	Integrated Roadside Vegetation Management
ODOT	Oregon DOT
SMA	Special Management Area
USFWS	U.S. Fish and Wildlife Service
WisDOT	Wisconsin Department of Transportation

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Photo Credits

Photo Number	Photo Title	Courtesy of
1-1	Roadsides can provide fritillary butterflies and other pollinators with habitat.	Nancy Lee Adamson, The Xerces Society
1-2	Diverse plantings with many flowers, such as this Iowa roadside, support the most pollinators.	Iowa Living Roadway Trust Fund/Maria Urice
1-3	Bumble bees are valuable pollinators of crop plants and wild plants alike. However, many species, including the southern plains bumble bee (Bombus fraternus), are in decline.	Jennifer Hopwood, The Xerces Society
2-1	Milkweed plants (Asclepias spp.) grow readily in roadsides. They are important as nectar sources for pollinators and as host plants for the monarch butterfly.	Jennifer Hopwood, The Xerces Society
3-1	Honey bees are important crop pollinators.	Nancy Lee Adamson, The Xerces Society
3-2	A flower fly on a coyote brush flower.	Mace Vaughan, The Xerces Society
3-3	Despite their value to ecosystem health and agricultural productions, we know very little about the status of most wild pollinators such as this long-horned bee (Melissodes spp.).	Mace Vaughan, The Xerces Society
3-4	Collisions with vehicles are one of several threats to pollinators associated with roads.	iStock.com/dlewis33
3-5	Spring wildflowers bloom along a Texas road, providing nectar and pollen as food sources for pollinators. In addition to providing food and shelter, roadside habitat can help to link other patches of habitat within the landscape.	Anne Stine, The Xerces Society
4-1	Remnant prairie on an Oklahoma roadside.	Jennifer Hopwood, The Xerces Society
4-2	A stand of native asters on a Florida roadside provides late-season nectar and pollen for pollinators.	Jeff Norcini
4-3	Reducing the frequency of mowing of vegetation beyond the clear zone benefits pollinators.	Jeff Norcini
4-4	Milkweed is an attractive component of roadside plantings and supports many pollinators.	MJ Hatfield
4-5	Native thistle species are highly attractive to many pollinators and are an important nectar source for monarch butterflies.	Oregon DOT Staff
4-6	Roadside remnant habitat is often home to unique plants that support unique pollinators, and mindful management can help maintain the diversity of the remnant habitat and protect pollinators.	Eleanor Dietrich
5-1	A diverse native roadside planting in Central Iowa.	Carl Kurtz
5-2	A diverse roadside in California with native wildflowers.	Jessa Kay Cruz, The Xerces Society
5-3	Living snow fences composed of shrubs such as willows can reduce snow drift and support pollinators.	New York State DOT
5-4	Signage to designate roadside plantings valuable to pollinators can be a valuable component of public relations.	Dianne Kahal-Berman/Ohio DOT
5-5	Native vegetation can support managed pollinators such as honey bees, as well as wild pollinators such as the monarch butterfly and leafcutter bee foraging on this milkweed flower.	John Anderson, Hedgerow Farms
6-1	Reducing mowing can increase aesthetics and reduce maintenance costs.	Nancy Lee Adamson, The Xerces Society
6-2	California roadside with native vegetation.	Jessa Kay Cruz, The Xerces Society
6-3	Iowa’s collaborative efforts to grow a local seed industry support the State’s efforts to restore roadsides to native prairie vegetation.	Iowa Living Roadway Trust Fund/Maria Urice
6-4	Planning ahead and controlling for invasive species before planting can increase the success of roadside revegetation projects.	Oregon DOT Staff
6-5	Although pollinators are killed by cars, increasing wildflowers in roadsides actually reduces pollinator road mortality.	Jeff Norcini
6-6	The value of native vegetation on roadsides extends beyond regional beauty. Native plants help the air, soil, and wildlife. Roadsides with native plants benefit the larger ecosystem as well as confer economic benefits to DOTs and communities.	Jeff Norcini

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Chapter 1 - Summary

Pollinators are critical to our food supply as well as to the health of ecosystems. Wild pollinators such as the monarch butterfly and a number of bumble bee species are in decline, and beekeepers in the United States and Europe have reported significant losses of managed European honey bee colonies. Pollinator declines are attributed to loss of habitat, pesticide exposure, diseases, parasites, and effects of introduced species. Roadsides can benefit pollinators by providing foraging habitat, places to breed, nest, and overwinter, and may act as corridors, linking patches of fragmented habitat.

Key steps that State Departments of Transportation (DOTs) and other transportation agencies can take to improve the quality of roadside habitat for pollinators include 1) adjusting roadside vegetation management techniques to accommodate pollinator resource needs, and 2) enhancing and restoring native roadside vegetation to include plant materials that improve pollinator habitat.

Pollinator-friendly roadside management practices such as reduced mowing and targeted herbicide use can reduce roadside maintenance costs. Roadsides with pollinator habitat features such as abundant flowering plants can draw tourists, resulting in positive economic benefits to States and local communities. Additionally, farmers and ranchers nearby may benefit economically from roadside habitat because of the ecosystem services such as pollination and pest control the habitat supports.

Roadsides managed with pollinators in mind can achieve multiple goals of stabilizing roadsides, reducing storm water pollution, supporting wildlife, and building public exposure and appreciation for the local landscape.

Ways to adjust roadside vegetation management practices to benefit pollinators:

• Inventory roadside vegetation, using tools such as global positioning systems, geographic information systems, roadside photo imagery, field surveys, and online resources and technology such as smartphone apps to help identify and record vegetation information.
• Protect the habitat that already exists. Identify remnant habitat and prioritize vegetation management in those areas to maintain and expand native vegetation.
• Inventory nonnative, invasive, and exotic vegetation to target them for control.
• Identify areas of high likelihood for successful pollinator-friendly plantings.
• Mow roadside vegetation as little as possible - at most no more than twice per year. Time mowing to minimize disruption to the life cycles of pollinators, especially State-listed, federally-listed, rare, endemic, sensitive, and declining species of pollinators.
• Delay mowing until the fall, preferably after first frost, to benefit a variety of pollinators by allowing flowering plants to bloom uninterrupted throughout the growing season and by reducing the risk of mortality by mower to larval stages of butterflies, moths, flower flies, and other pollinators that reside on vegetation.
• Reduce herbicide use and subsequent impacts of herbicides on pollinators by using selective herbicides, spot-spray applications, and timing applications to the most vulnerable life stage of the weed.
• Provide vegetation maintenance crews with plant identification tools and training to recognize native plants as well as invasive weeds in order to reduce unintended damage to non-target plants during herbicide use.
• If sheep or goats are used to graze invasive weeds on roadsides, take into consideration the timing of the life cycles of rare, endemic, sensitive, and declining species of pollinators.
• If prescribed burns are used, use rotational burning every 3 to 5 years to allow time for pollinator populations and their habitats to recover.
• If biological control agents are used to control weeds, use only those agents that have not demonstrated plant host expansion beyond the target weed.
• If haying occurs in your State, limit it to once a growing season and restrict it in areas that support rare and declining pollinator species.
• Specific conservation measures are needed to protect State- or federally-listed pollinator species, but these measures may also generally benefit pollinators.

Implementation methods and tools:

• Implement pilot projects to test the effectiveness of reduced mowing and/or reduced herbicide strategies.
• Provide education and training about the economic and ecological value of reduced mowing to DOT staff, including administrators, State engineers, resident engineers, and district engineers.
• Identify technologies from other DOTs that have successfully implemented reduced mowing and other pollinator-friendly practices and reach out to roadside managers at those States for information exchanges.
• Provide training to roadside managers about herbicide applications, including the timing of applications and selection of chemicals for particular weeds.
• Provide training for native plant identification and invasive species identification.
• Partner with local botanical experts, State agencies, and/or universities to conduct roadside surveys with maintenance staff and share resources.
• Collaborate with State agencies or local conservation organizations to gain training from experienced land management experts and/or to implement certain technologies such as grazing and prescribed burns.
• Develop strategies for public outreach, especially to adjacent landowners, about the benefits of reduced mowing or other management activities. This may include signage, public service announcements, and written print and electronic materials.

Ways to enhance and restore native vegetation along roadsides to benefit pollinators:

• Prioritize the use of native plants in erosion control and landscape projects.
• Increase the diversity and abundance of native flowers on roadsides, especially flowering plants that benefit pollinators. Seed mixes for erosion control projects are best if they have at least 50% wildflower component, and landscape projects are best with higher than 50% densities of flowering plants.
Photo 1-3: Bumble bees are valuable pollinators of crop plants and wild plants alike. However, many species, including the southern plains bumble bee (Bombus fraternus), are in decline.
• Select flowering species that have sequential and overlapping bloom times to provide resources for pollinators throughout the growing season.
• Include plant species known to provide quality forage to pollinators or nesting materials.
• Include butterfly and moth host plants (e.g., milkweeds for monarch butterflies).
• Prioritize the use of locally sourced plant material, which can improve establishment and persistence of plantings and have higher value to pollinators.
• Avoid compromising highway safety by maintaining a regularly mown strip of vegetation adjacent to the pavement, avoiding tall plants in high crash zones and within lines of sight, avoiding planting species that are palatable to deer, and installing living snow fences to help reduce drifting snow.
• Prioritize sites for new high quality roadside restorations to maximize restoration success and use resources effectively. Select roadside sites that have low to moderate weed pressure, are wide, are not going to be subject to construction, and will not be impacted by adjacent land use such as pesticide drift.
• By starting with small projects and forming partnerships with restoration experts in State agencies or local conservation organizations, DOTs with limited restoration experience can develop internal expertise and expand by building off of successful projects.

Implementation methods and tools:

• Training in native plant establishment and/or partnerships with experts that can help build internal expertise.
• Increase support within State DOTs for the use of native plants in roadside plantings by providing education about the economic and ecological values of native plants and access to tools for implementing revegetation using native plants.
• Identify funding eligibilities for the use of native plants in roadside plantings.
• Plan ahead to develop restoration plans and seed mixes. Then, reach out to local native seed vendors to communicate future plant material needs in advance.
• Partner with other agencies and organizations to develop and grow a local native seed industry to support DOT plant material needs.
• Establish commitments to purchase and plant State-origin or region-origin seed to help stabilize the native seed market, while also increasing production and reducing costs.
• Maintain eco-regional plant lists of species suitable for roadside plantings that include species that provide nectar, pollen, or act as host plants for pollinators that will establish well under varying conditions, will not become weed problems or disease vectors for adjacent lands, and are of short or moderate stature to allow for sight lines along roadways.
• Communicate the economic and ecological benefits of using native plants to the public, especially to adjacent landowners. Efforts might include signage, public service announcements, written print and electronic materials, or tourism campaigns highlighting showy plantings.
• Form partnerships with public agencies and private organizations to provide education and outreach opportunities to the public.

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Chapter 2 - Introduction

Report Context

Concerns about the declines of managed honey bees and wild native pollinators, such as monarch butterflies, have focused attention on the importance of habitat restoration and management in the conservation of pollinators and the ecosystem services they provide. Roadsides form one of the most extensive networks of linear habitats on earth, and in the United States, roadside rights-of-way managed by State DOTs cover an estimated 17 million acres (Ament et al. 2014). Roadsides can provide habitat for pollinators, offering food, breeding, or nesting opportunities, and can also aid dispersal of pollinators by linking fragmented habitats. Typically dominated by early-successional plant communities, roadsides can support a diversity of generalist pollinators, including bumble bees, honey bees, and butterflies as well as rare or federally-listed species.

Not all roadsides are equally beneficial to pollinators. Roadsides that are intensively mown, blanket-sprayed with herbicides, or planted with introduced grasses support far fewer species of pollinators and smaller population densities than roadsides managed for native plants. Roadside vegetation management influences how pollinators use roadsides, and even influences the number of pollinators killed by vehicles driving nearby. Researchers in Europe found that the frequency of mowing was linked to the proportion of butterflies killed on roads because butterflies that had to disperse to find new habitat after roadsides were mowed had a greater likelihood of collisions with vehicles. In contrast, roadsides with more species of plants had fewer butterflies killed by traffic. By reducing the need for pollinators to disperse elsewhere to find food or nesting sites, high quality roadside habitat may reduce the numbers of pollinators killed by vehicles.

There are two fundamental approaches to improving the quality of roadside habitat for pollinators: 1) adjusting vegetation management to accommodate pollinator resource needs, and 2) enhancing and restoring native vegetation along roadsides. Here we provide best management practices for managing roadside vegetation to reduce impacts to pollinators. This includes implementing roadside plantings that provide functions, including erosion control and motorist safety, while also benefiting pollinators. We also outline challenges to implementation identified by State DOTs and roadside restoration experts, and discuss potential opportunities to overcome these challenges. Additionally, we include case studies from across the United States.

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Report Development

The Xerces Society for Invertebrate Conservation and ICF International staff performed a thorough literature review of peer-reviewed and technical material and conducted interviews with State DOTs and roadside restoration experts who work with DOTs. The literature review included a comprehensive treatment of the status of pollinators, causes of decline, potential mitigation efforts, habitat restoration and management for pollinators, and applications to highway rights-of-way. The interviews provided documentation of existing roadside vegetation management practices, including information on the current State of the practice in roadside vegetation management as relates to pollinators. The interviews also provided feedback about the feasibility of implementing roadside vegetation management strategies that can benefit pollinators, highlighting both successes and challenges in improving pollinator habitat. This report is based on information identified in the literature review and obtained through the interviews.

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Report Organization

These best management practices are intended as a starting point for State DOTs looking to make roadsides more pollinator-friendly. This report is organized around the key findings of the literature review and the interview report. Chapter 3, A Primer on Pollinators and Pollinator Use of Roadside Habitat, provides background information on pollinators, their biology, their decline, and threats to pollinators, as well as how pollinators use roadsides and the potential contributions of roadside management and restoration to pollinator conservation. Chapter 4, Roadside Vegetation Management and Pollinators, outlines best management practices for managing roadside vegetation to reduce harm to pollinators. Chapter 5, Using Native Plants to Restore Roadsides for Pollinators, outlines best management practices for roadside plantings that support pollinators. Chapter 6, Overcoming Obstacles to Implementing Pollinator-Friendly Practices, outlines obstacles to implementation of pollinator-friendly practices, along with tools and resources to mitigate challenges to implementation. Chapter 7, Resources for Roadside Management for Pollinators, provides resources; Chapter 8, Contributors, provides details about the authors of this report; and Chapter 9, References Cited, provides a comprehensive list of references.

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Chapter 3 - A Primer on Pollinators and Pollinator Use of Roadside Habitat

Importance of Pollinators

The ecosystem services provided by pollinators are essential to human wellbeing, agricultural production, and ecosystem health. An estimated 85% of the world’s flowering plants depend on animals - mostly insects - for pollination (Ollerton et al. 2011). Pollinators sustain wildland plant communities that provide food and shelter for myriad other wildlife. Pollinators are an indispensable component of a healthy environment.

Pollinators are also crucial to agriculture and to our diet. More than two-thirds of crop species are dependent upon pollinators, including crops that produce fruits, vegetables, spices, nuts, seeds, and livestock forage (Klein et al. 2006). From the coffee you drink in the morning to the apple pie you have for dessert, an estimated one-in-three mouthfuls of food and drink that you consume come from a pollinator-dependent crop (McGregor 1976; Klein et al. 2006). In fact, the most nutritious parts of our diet, the fruits and vegetables, are the products that are most dependent upon insect pollination. The majority of minerals, vitamins, and nutrients we need to maintain our health (such as vitamin C, calcium, and folic acid) come from crop plants that depend partially or fully on animal pollinators (Eilers et al. 2011). The value of insect crop pollination is estimated to be up to $27 billion in the U.S. (Morse and Calderone 2000; Losey and Vaughan 2006).

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Pollinator Biology

Pollination is a mutually beneficial interaction between plants and pollinators. Animals visit flowers seeking sustenance, and in the process transfer pollen grains which allow flowering plants to reproduce. Sugary nectar and/or protein-packed pollen grains are food resources for pollinators (see Table 3-1). The great majority of pollinators are insects, including bees, wasps, flies, beetles, butterflies, and moths (Allen-Wardell et al. 1998; Kevan 1999; Kearns 2001), but many bird and bat species pollinate as well (Grant 1994; Valiente-Banuet et al. 2004). Bees are considered the most important group of pollinators for agricultural crops (Morse and Calderone 2000; Garibaldi et al. 2013) as well as for wild plants in temperate climates (Michener 2007). Bees are the most important pollinators because 1) they collect both pollen and nectar (most insects just visit flowers to drink nectar), 2) they forage in and around a nest 3) they make more trips to flowers as they are foraging to collect provisions for a nest and 4) they have more flower constancy, i.e., once they find a good forage source they visit that type of flower over and over.

The domesticated European honey bee (Apis mellifera L.) is the most well-known of all bees. This bee has been managed for honey production for hundreds of years and has also become widely managed for crop pollination. Honey bees contribute more than $15 billion in crop production annually in the United States (Morse and Calderone 2000). There are also approximately 4,000 species of wild, native bees in North America (Michener 2007), and many are also important crop pollinators (Tepedino 1981; Bosch and Kemp 2001; Javorek et al. 2002; Winfree et al. 2008; Garibaldi et al. 2013). Native bees are important in the production of an estimated $3 billion worth of crops annually to the United States economy (Losey and Vaughan 2006; Calderone 2012), and emerging research shows that this is likely an underestimate of their total economic contributions (Chaplin-Kramer et al. 2011). A recent analysis of 41 crop systems worldwide found that managed honey bees do not replace the pollination services provided by a diverse community of native bees (Garibaldi et al. 2013). Additionally, native bees are often more efficient than honey bees on an individual bee basis at pollinating particular crops, such as squash, berries, and tree fruits (Tepedino 1981; Bosch and Kemp 2001; Javorek et al. 2002; Garibaldi et al. 2013).

Of the other orders of pollinating insects, flies (Diptera) also provide substantial pollination services (Speight 1978; Kearns 2001; Larson et al. 2001), especially in alpine areas and tundra. Other insects such as beetles (Coleoptera) and wasps (Hymenoptera) provide pollination services, though to a lesser extent (Frankie et al. 1990; Irvine and Armstrong 1990; Kevan 1999). The contribution of most butterfly and moth species (Lepidoptera) to pollination services is unknown (Jennersten 1988; Frankie et al. 1990; Allen-Wardell et al. 1998; Westerkamp and Gottsberger 2000), but there are instances where butterflies have been documented pollinating wild plant species, including some flowering plants specially adapted for butterfly pollination (e.g., Russelia, Phlox, and Lantana; Fallon et al. 2014). Many butterfly species take long flights between flowers and may carry pollen for a long time, and they may be effective as dispersers of pollen.

In addition to insect pollinators, there are two groups of nectar-feeding vertebrates that play an important role in pollination: hummingbirds and bats. There are 12 species of nectar-feeding bats that are known pollinators in North America and Mexico (National Research Council 2007). The known ranges for these bats corresponds closely with the distribution of columnar cacti (e.g., saguaro [Carnegiea gigantea], Pachycereus spp., Stenocereus spp., Lophocereus spp.) and agaves (Agave spp.), the main species they are known to pollinate (Valiente-Banuet et al. 2004), primarily in the deserts of Arizona, California, Nevada, New Mexico, and Texas. Hummingbirds, which pollinate about 130 native plant species with flowers adapted for hummingbird pollination, make long migratory journeys in North America and depend on nectar corridors to meet the energy demands they undergo to sustain their long-distance movements (Nabhan et al. 2004).

Table 3-1. Pollinator Habitat Needs

Pollinators	Food	Shelter
Bumble bees	Nectar for adults; nectar and pollen collected as provisions for larvae	Nest in small cavities, underground in abandoned rodent nests, under clumps of grass, or in hollow trees, bird nests, or walls
Ground-nesting bees	Nectar for adults; nectar and pollen collected as provisions for larvae	Nest in bare or partially vegetated, well-drained soil
Tunnel-nesting bees	Nectar for adults; nectar and pollen collected as provisions for larvae	Nest in narrow tunnels in dead standing trees, or excavate nests in pith of stems and twigs. Some construct domed nests of mud, plant resins, saps, or gums on the surface of rocks or trees
Beetles	Pollen and nectar as adults; vegetation as larvae or prey such as aphids, slugs, insect eggs	Larvae overwinter in loose soil or leaf litter Adults shelter under rocks, logs, brush
Butterflies and moths	Vegetation of larval host plants; nectar; some males obtain nutrients, minerals, and salt from rotting fruit, tree sap, animal dung and urine, carrion, clay deposits, and mud puddles	Host plants; protected site such as a tree, bush, tall grass, or a pile of leaves, sticks, or rocks
Flies	Nectar and sometimes pollen as adults; insect prey such as aphids, scales, mites, thrips as larvae	Larvae found on plants near prey Pupae and adults overwinter in soil or leaf litter
Wasps	Nectar as adults; insect prey such as caterpillars, aphids, grasshoppers, planthoppers, and true bugs as larvae	Many nest in the ground; others nest in tunnel nests in wood or cavities in mud or resin
Bats	Nectar, pollen, fruit	Caves and mine shafts, trees, and various structures including bridges
Hummingbirds	Nectar, insects, tree sap, spiders, caterpillars, aphids, insect eggs, and willow catkins	Trees, shrubs, and vines near suitable foraging habitat
Adapted in part from Marks 2006; Mader et al. 2014

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Pollinator Decline

Globally, pollinators are in decline (Biesmeijer et al. 2006; National Research Council 2007; Potts et al. 2010). Pollinator declines are attributed to the loss, degradation, and fragmentation of habitat (Kremen et al. 2002; Potts et al. 2010); introduced species (Memmott and Wasser 2002; Tallamy and Shropshire 2009); the use of pesticides (Kevan 1975; Pisa et al. 2015); habitat disruption from grazing, mowing, and fire (Potts et al. 2005; Johst et al. 2006; Hatfield and LeBuhn 2007); and diseases and parasites (Altizer and Oberhauser 1999; Colla et al. 2006; Cameron et al. 2011).

In the U.S., the number of honey bee colonies has been in decline over the past half-century because of disease, parasites, lack of floral resources, insecticides, and other factors (National Research Council 2007). Since 2006, beekeepers have experienced record high annual hive losses of 29% or more (Bee Informed Partnership 2014).

Though little is known about the status of most of North America’s pollinators, what data does exist suggests that numerous species are experiencing declines similar to or more severe than the declines seen in honey bees. One-quarter of North America’s bumble bees have experienced significant declines (Hatfield et al. 2014), including declines in species that were formerly some of the most common species (Evans et al. 2008; Grixti et al. 2009; Cameron et al. 2011).

Monarch butterflies (Danaus plexippus) in North America are vulnerable to extinction, according to a recently completed assessment funded by the U.S. Forest Service and undertaken by NatureServe and the Xerces Society for Invertebrate Conservation (Jepsen et al 2015). Monarch butterfly populations have dropped by 90% east of the Rocky Mountains (Rendon-Salinas and Tavera-Alonso 2014) and by 50% west of the Rockies (Monroe et al. 2014). Three factors appear most important to explain the decline of eastern monarchs: loss of milkweed breeding habitat due to increased use of herbicides on genetically modified herbicide-resistant cropland and land conversion, logging at overwintering sites, and an increase in extreme weather events (Jepsen et al 2015). The loss of milkweeds, the monarch’s required larval host plants, has been significant, particularly within agricultural fields (Hartzler 2010; Pleasants and Oberhauser 2012).

Other butterfly species have also seen significant declines. NatureServe (a primary source for species conservation data, status, and trends in the United States) has assessed all 800 butterfly species in the United States and has found that 141 (17%) are at risk of extinction (NatureServe 2014). Twenty-six species of butterflies are listed as threatened or endangered under the Federal Endangered Species Act (U.S. Fish and Wildlife Service 2014). Some studies are also showing regional declines in butterfly species (Forister et al. 2011).

The populations of both hummingbirds and nectar-feeding bats throughout the southwestern United States have also experienced declines (National Research Council 2007). Hummingbirds face disruption of migratory routes and loss of habitat (Calder 2004), while nectar-feeding bats face disturbance of their roost sites and removal of foraging habitat and nectar sources (U.S. Fish and Wildlife Service 2006).
The loss of pollinators negatively affects plant reproduction and plant community diversity (Bawa 1990; Fontaine et al. 2005; Brosi and Briggs 2013). Threats to pollinators may have profound consequences for ecosystem health as well as our food systems (Kearns et al. 1998; Spira 2001; Steffan-Dewenter and Westphal 2008).

The loss of pollinators negatively affects plant reproduction and plant community diversity (Bawa 1990; Fontaine et al. 2005; Brosi and Briggs 2013). Threats to pollinators may have profound consequences for ecosystem health as well as our food systems (Kearns et al. 1998; Spira 2001; Steffan-Dewenter and Westphal 2008).

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Roadsides and Pollinator Conservation

Concerns about pollinator decline and its repercussions have led to increased efforts to reduce threats to pollinators. Managing existing habitat for pollinators and restoring additional habitat has been demonstrated to increase pollinator abundance and diversity (Fiedler et al. 2012; Klein et al. 2012; Morandin and Kremen 2013), and roadsides are a conservation opportunity to increase pollinator habitat. Roadsides provide several ecological functions for pollinators, including serving as foraging habitat, providing breeding or nesting opportunities, and aiding dispersal of pollinators by linking fragmented habitats.

Pollinator Food Sources

Flowering plants in roadsides are important sources of nectar and pollen for pollinators that reside within the roadside habitat (Munguira and Thomas 1992) as well as those that use the roadside as a partial habitat and reproduce or overwinter elsewhere (Ouin et al. 2004). Roadsides have the potential to provide resources needed for all life stages (e.g., host plants, nectar plants, and overwintering habitat for butterflies). For example, roadsides can wholly support butterfly and moth populations if nectar and host plants are sufficiently abundant (Munguira and Thomas 1992; Saarinen et al. 2005). Roadsides can also provide food for managed honey bees. Honey bee colonies require diverse sources of pollen and nectar, and a lack of forage is frequently cited as a primary contributing factor to declines in honey bee health (National Research Council 2007).

The availability of floral resources influences the abundance and diversity of butterflies (Saarinen et al. 2005) and bees (Hopwood 2008) found on roadsides. A diversity of flowers with a succession of bloom throughout the growing season benefits wild pollinators such as solitary bees and monarch butterflies, as well as managed honey bees, which benefit from a diversity of pollen sources to maintain a healthy immune system (Alaux et al. 2010; Di Pasquale et al. 2013).

Shelter and Nest Sites

Roadsides can also provide shelter, sites for nesting or egg-laying, or overwintering habitat. Bees provide for their young by constructing nests in which their offspring develop. Many ground-nesting bees prefer to nest in sunny, bare patches of soil (Linsley 1958). Such patches can be found around the bases of native bunch grasses such as little bluestem (Schizachyrium scoparium) that tend to grow in dense bundles, leaving small areas of bare ground exposed between plants. Hopwood (2008) found that ground-nesting bees in Kansas were more common in roadsides with native plantings. In contrast, roadsides with a tight sod of brome or other nonnative cool season grasses had fewer ground-nesting bees.

Roadside vegetation can also provide habitat for tunnel-nesting bees, which nest in hollow or pithy stems or other small cavities. Bumble bees require a small, insulated cavity, such as underneath grass clumps (Svennson et al. 2000) or under the thatch of bunch grasses (Hatfield et al. 2012).

The breeding and overwintering habitat needs are less understood for other groups of pollinators, but Schaffers et al. (2012) has recorded syrphid fly species and soldier beetles overwintering in roadside soil or litter. Butterflies and moths may also utilize roadsides as overwintering habitat (Schaffers et al. 2012) or shelter (Saarinen et al. 2005).

Landscape Connectivity

Landscape connectivity is important for the populations of many species, but due to urbanization, agricultural intensification, and other human activities, habitat is becoming increasingly fragmented (Saunders et al. 1991). Roadsides extend across a variety of landscapes, often contain greater plant diversity than adjacent lands, and are generally excluded from further development and major disturbances. In developed landscapes, such as intensively managed agricultural lands, roadsides may provide areas of refuge for pollinators in an otherwise inhospitable environment. The linear shape and connectivity of roadsides may help pollinators move through the landscape, either for daily foraging or for dispersal to larger habitat patches (Dirig and Cryan 1991; Ries et al. 2001; Hopwood et al. 2010).

Threats to Pollinators from Roadsides and Roadside Management

Roads can pose specific threats to pollinators. Roadside vegetation management can be harmful to pollinators (Johst et al. 2006). Roads can be a source of mortality for pollinators due to collisions with vehicles (Munguira and Thomas 1992). Roads fragment and degrade habitat (Trombulak and Frissell 2000). Roads may act as barriers to pollinator movement (Valtonen and Saarinen 2005). The prevalence of invasive and nonnative species on roadsides reduces pollinator abundance and diversity (Hopwood 2008). Finally, roadsides are exposed to pesticide drift from adjacent land (Krupke et al. 2012) and to pollution from vehicles (Jablonski et al. 1995). Despite these threats, roadsides provide an opportunity to increase pollinator habitat and contribute to pollinator health. The roadside management practices outlined in this document lessen the negative impacts of many of these threats.

Future Conservation Opportunities in Roadside Management

Roadside habitat restoration and modification of roadside vegetation management practices can mitigate the threats to pollinators that are associated with roads. For example, managing roadsides to maximize plant diversity through the judicious use of mowing and spot-spraying of herbicides can promote pollinators. Roadsides with remnant or restored vegetation can lessen the effects of habitat fragmentation by functioning as corridors and connecting larger habitat patches (Forman et al. 2003; Huijser and Clevenger 2006). Additionally, if roadside restorations contain floral resources, pollinators will be less likely to seek habitat elsewhere, reducing their risk of being killed by vehicles (Ries et al. 2001; Skorka et al. 2013). The removal of invasive species increases pollinator abundance and diversity (Hanula and Horn 2011; Fiedler et al. 2012), and roadside restorations that replace invasive plants with native vegetation improve pollinator habitat.

Roadsides can provide quality habitat for a diverse community of pollinators if managed with care. Managing roadsides with pollinators in mind can also benefit other insects that contribute to crop pest control as well as songbirds and game birds. As patches of refuge for pollinators in otherwise inhospitable landscapes, roadside habitat can contribute to the maintenance of healthy ecosystems and provision of ecological services such as crop pollination.

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Chapter 4 - A Primer on Pollinators and Pollinator Use of Roadside Habitat

Overview

Roadside vegetation management during the growing season can adversely affect pollinators. Mowing, herbicide use, prescribed burning, and grazing all remove flowering plants that pollinators rely on for food. For example, mowing or conducting a prescribed burn during the growing season  will also destroy larval pollinators present on plants (e.g., caterpillars on host plants) as well as the nests of tunnel-nesting bees and bumble bee colonies.

There are adjustments that can be made to keep roadside vegetation management cost effective and safe for motorists while also reducing harm to pollinators. Roadside inventories can identify existing habitat that is valuable to pollinators, sites in need of invasive species management, and potential sites for future wildflower plantings. The timing and frequency of mowing can be adjusted to accommodate pollinators. The use of spot-spraying herbicides and adoption of spray technologies can reduce off-target herbicide use and protect flowering plants and host plants valuable to pollinators. Grazing and prescribed burns can be timed to reduce impacts to any rare or declining pollinator species in the region as well as the general pollinator community. Integrated roadside vegetation management strategies used to support plant diversity will benefit pollinators.

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Roadside Vegetation Inventories

A roadside vegetation inventory to map plant species of interest provides information to roadside managers that can improve roadside management. All plants of interest ideally would be included in inventories, including native species, invasive species, and noxious plants. Global positioning systems (GPS) and geographic information systems (GIS) are powerful tools that can improve the efficiency of inventories. Vehicle-mounted photographic equipment allows vegetation and GPS locations to be recorded easily and reviewed at a later date. Or personnel might inventory roadside vegetation by traveling roadways and entering the GPS data to record various attributes of the roadside vegetation while another person is driving. There are some limitations with using photos or driving surveys to characterize vegetation, and true inventories and assessments involve walking among the plants in the roadside. Photo or driving surveys can be followed with targeted field surveys if needed.

However the information is obtained, the establishment of baseline vegetation conditions and locations allows managers to make informed management decisions, target management operations to reduce costs, effectively evaluate conditions for future projects, share vegetation information between agencies, and assess the effectiveness of management activities over time.

Remnant Habitat

Roadside vegetation inventories can identify remnant habitat, which is portions of the natural habitat that was once present on a much larger scale before development took place. Because remnants are the last remaining patches of intact habitat, they often have high conservation value. Rare plants, and rare animals that depend upon those plants, may reside in roadside remnants.

Identification of remnant habitat can allow roadside managers to make informed decisions about how to manage remnant habitat to allow it to persist, to help sensitive species to survive, and to comply with applicable State or federal protection laws. Pollinators that are habitat specialists, with very specific habitat needs, particularly benefit from the preservation of roadside remnants.

Informed management of remnant roadside habitat can transform a degraded roadside remnant into a diverse, high quality roadside. Often a remnant just needs a carefully timed mowing or prescribed burn to return it to a diverse stand of native plants. Florida DOT has recently adopted a new procedure to focus on identifying naturally occurring wildflower areas and managing those areas with care. In Nebraska, where portions of remnant prairie have been identified along Nebraska Department of Roads rights-of-way, spraying and mowing are restricted until after October 1 (NDOR 2014). Delaying disturbance until the fall allows the wildflowers and grasses to produce seeds and complete their life cycles.

Once identified, signage can help indicate roadside remnant habitat. Texas DOT uses signage to indicate roadsides with rare plant species. Oregon DOT (ODOT) designates Special Management Areas to protect threatened and endangered plants on rights-of-way, using signage to indicate the approved site-specific management strategies.

Invasive and Noxious Weeds

Many nonnative and invasive plants are disproportionately present in roadsides, where they have optimal conditions for invasion and dispersal (Tyser and Worley 1992; Hansen and Clevenger 2005). Invasive plants that displace native species can decrease the quality of roadside habitat for pollinators (Valtonen et al. 2006; Hopwood 2008). Inventories can aid in control of invasive and noxious weeds by identifying locations where eradicative measures are needed, and through the monitoring of sites over time to evaluate effectiveness of management efforts.

Priorities for Future Restorations

Roadside inventories can help inform and direct future plantings, and can be used to identify rights-of-way that might be candidates for future revegetation efforts. For example, inventories can help pinpoint possible locations for pollinator plantings. If the objective is to provide a biological corridor for pollinators, DOTs can work with State agencies or conservation organizations to determine stretches of road between existing habitat patches to target for plant restoration. If the goal is to establish wildflower plantings to support pollinators, inventories can help with the selection of sites that meet criteria that will maximize the effectiveness of the planting, such as visibility to the public, moderate to low weed pressure, and adjacent to land that does not pose a threat to the persistence of the planting.

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Pollinators and Integrated Roadside Vegetation Management

Once current roadside conditions and composition of vegetation is assessed, vegetation management plans can be developed. State DOTs may want to develop Integrated Roadside Vegetation Management (IRVM) plans. Because IRVM involves tailoring management to specific site conditions, an IRVM program can be very compatible with pollinator protection. By encouraging plant diversity and reducing mowing and herbicide use, IRVM improves the quality of the roadside habitat. IRVM practices that limit disturbance but maintain plant diversity, such as spot mowing to reduce weed seed production, limited grazing, and occasional prescribed fire, will likely also benefit pollinators. Species mixes that have been designed for IRVM plantings can fulfill functional roles that are valuable to roadside vegetation management but can also support pollinators.

Of the nine State DOTs we interviewed as part of this project, five—California, Iowa, Idaho, Oregon, and New York—have formal IRVM programs that are supported by policy, training, and guidance documents. The four agencies without a formal IRVM program—Arizona, Florida, Ohio, and Minnesota—report using some aspects of IRVM.

Mowing Recommendations

Adoption of a reduced mowing regime for the vegetation beyond the clear zone is one of the most significant changes that State DOTs can make to benefit pollinators. When roadside mowing occurs during the growing season, it can directly kill pollinators in the egg or larval stages, such as butterfly caterpillars or bumble bee larvae within their colony’s nest, because they cannot escape the mower (Humbert et al. 2010; Hatfield et al. 2012). The indirect impacts on pollinators through the temporary removal of flowering plants that provide nectar and pollen and butterfly host plants are even greater (Johst et al. 2006).

Although mowing during the growing season can be harmful to pollinators, limited mowing can also be beneficial to pollinators by rejuvenating wildflower populations and keeping woody plants from invading (Parr and Way 1988; Noordijk et al. 2009). Without some management intervention, roadside vegetation may become degraded by the encroachment of woody plants or by the invasion of noxious weeds. Mowing is an effective management tool to prevent vegetative succession and to help control weed populations. Strategic reduced mowing and consideration of the timing of mowing can improve roadside habitat quality for pollinators.

Beyond value to pollinators, reducing mowing can provide DOTs with significant cost savings. In 2011-2012, Florida DOT spent $13 million on roadside mowing. The University of Florida, Institute of Food and Agricultural Sciences report, "Economic Impact of Ecosystem Services Provided by Ecologically Sustainable Roadside Right of Way Vegetation Management Practices," found that Florida DOT could reduce its costs by 30% by implementing sustainable management practices such as reduced mowing (Harrison 2014).

Despite the economic and ecological benefits that reducing roadside mowing provides, it may not be adopted readily due to concerns that reduced mowing may increase dangerous animal-vehicle collisions. Common perceptions about reduced mowing include 1) that the unmown roadside vegetation will harbor more deer or other large herbivorous mammals that can be involved in vehicle crashes and 2) motorists will have greater difficulty viewing and avoiding animals entering the road.

In contrast to these perceptions, data indicates that reduced mowing of the entire roadside right-of-way may not influence deer-vehicle crash frequency. For example, researchers comparing deer-vehicle crash frequency data before and after reduced mowing was implemented in two Northeastern States found no relationship between mowing regime and crashes (Barnum and Alt 2013). In a Mississippi study comparing mowing and deer presence in roadside plant communities, researchers found that deer preferred the plots mowed four times a year over the plots mowed only once, though there were no significant differences in the height of the vegetation in the treatment plots three weeks after each mowing (Guyton et al 2014). Mowing can increase the palatability of some plants, thus increasing foraging by deer in roadsides (Mastro et al. 2008).

Frequency and Timing of Mowing

Pollinator abundance and diversity found on roadsides is tightly linked to roadside floral abundance and the number of flowering plant species (Ries et al. 2001; Hopwood 2008). Mowing regimes that encourage plant diversity also benefit pollinators. In contrast, frequent mowing reduces wildflower bloom, stunts plant growth, and over time, leads to reduced wildflower diversity and density, which can negatively impact pollinators (Gerell 1997 ; Saarinen et al. 2005). Additionally, frequent mowing can be very costly (Harrison 2014).

To reduce harm to pollinators, roadsides mown no more than twice a growing season are ideal. Mowing a site only once a year, or even every other year, would have the least impact on pollinators. If weed management is the goal, mowing could be limited to patches of weeds and timed to reduce seed production (Brandt et al. 2011). Mowing techniques that reduce mortality of birds and small mammals, such as reduced mower speed, a high swath height (6 inches or higher), or the use of a flushing bar may also reduce risk to pollinators to some degree.

Some States have a reduced mowing policy that restricts the frequency of mowing or stipulates a time frame when mowing may be conducted. For example, in Minnesota, where concerns over declining pheasant habitat sparked adoption of a reduced mowing law, road authorities can only conduct mowing of the entire right-of-way between July 31 and August 31, a timing which reduces damage to grassland bird nests.

Timing roadside mowing to benefit pollinators can be a balancing act between other management priorities and the habitat needs of other wildlife. Delaying mowing until autumn after the first frost will benefit a variety of pollinators by allowing flowering plants to bloom uninterrupted throughout the growing season (Valtonen et al. 2006; Johst et al. 2006). It also reduces the risk of mortality by mower to larval stages that reside on vegetation (e.g., butterfly caterpillars, larval flower flies). However, it is difficult for many State DOTs in central and northern regions to conduct mowing in the fall when they are transitioning to winter operations. Some States contract out mowing operations, and this may be one way to free up staff to ready for winter and also avoid impacts to pollinators. Ultimately, State DOTs need some flexibility on when to mow during the growing season, in order to balance all the competing priorities for their time.

Timing mowing to reduce impacts on pollinators will vary from region to region. A single mow in Kansas in July can knock back dominant grasses and promote wildflower growth (Collins et al. 1998). In Texas, a mow in spring after the first bloom and then a second mow in the fall can stimulate wildflower propagation. In California or other arid regions, it might be most appropriate to mow after the first rain or when the relative humidity is high to avoid fires started by mowers.

Milkweeds, host plants of monarch butterflies, can commonly be found growing in roadsides (Hartzler 2010). Mowing of roadsides can influence the value of the roadside habitat for monarch butterflies by reducing host plant abundance as well as nectar sources. Mowing may be particularly detrimental for monarchs if it takes place during peak reproduction times, for example, between mid-March and early May in Texas (See Figure 4-1 for windows when mowing has the least impacts on the reproduction of monarchs). In upstate New York, mowing common milkweed in July spurred regrowth of the milkweed and increased monarch butterfly caterpillar development over unmown milkweeds (Fischer et al. 2015). In Oklahoma, a mid-summer mow or burn will promote milkweed growth that can support late summer monarch breeding (Baum and Mueller 2015).

If roadside habitat or vegetation is known to support endangered or rare and sensitive pollinator species, such as the Karner blue butterfly (Lycaeides melissa samuelis) or regal fritillary (Speyeria idalia), mowing should be timed to minimize disruption to the life cycle of the species as much as possible. For a full list of pollinator species listed under the authority of the Endangered Species Act, please see the U.S. Fish and Wildlife Service web page at https://www.fws.gov/story/highlighting-importance-pollinators.

Figure 4-1. Regional Recommendations for Times to Mow Based on the Timing of the Monarch Butterfly Lifecycle

Management Windows Windows when mowing may be safer for monarchs in spring, summer, and fall by regions (separated primarily by latitude). These windows are based on timing of breeding activity and peak migration. Options in [ ] are recommended only if necessary. Mowing at these times may still kill monarchs but that mortality would be minimized. Variation from year to year may occur. This data is based on long-term trends from the Monarch Larva Monitoring Project.

Reprinted with permission by the Monarch Joint Venture.

Herbicide Recommendations

Used indiscriminately, herbicides can reduce the quality of habitat by removing floral resources and host plants, and may be directly toxic to some pollinators (Smallidge and Leopold 1997; Kearns et al. 1998; Stark et al. 2012). Overuse of herbicides can also weaken stands of vegetation, making them more vulnerable to weed invasions (Brandt et al. 2011), which also indirectly affects pollinators. However, herbicides are a cost-effective vegetation management tool and are the only tools available to control some noxious weeds. Judicious herbicide use can suppress undesired vegetation while maintaining diverse habitat. Roadside managers can protect pollinators by targeting herbicide applications, timing applications effectively, managing herbicide drift, and working with adjacent landowners to reduce disturbances that cause weed invasions in the rights-of-way.

To limit the destruction of pollinator host plants or forage plants, avoid broadcast spraying or pellet dispersal. Spot treatment of individual invasive or noxious weeds or woody plants with a backpack sprayer, weed wiper, or similar appropriate technology can target weeds without weakening non-target species. Manage herbicide drift by calibrating equipment regularly, using precision equipment for applications, maintaining a buffer zone of 30 feet or more near sensitive vegetation and avoiding applications if winds are at or above 15 mph (Marrs et al. 1993; Harper-Lore et al. 2014).

Use selective herbicides whenever possible to reduce damage to non-target plants. Apply herbicides at the stage of growth when the weed is most vulnerable, when application will be most successful. For many weeds, this will be the seedling stage.

Training is a key component to reducing herbicide use. Applicators need training to help them determine the preferred herbicides, the best timing for weed control in each situation, and to improve the efficacy of herbicide use. New technologies can target the delivery of herbicides, and GPS/GIS systems can help roadside managers track sensitive sites as well as weed issues. Annual training can keep crews up to date on new technology.

Plant identification of invasive weeds and native vegetation are also important to be included in training. Some noninvasive, native plants that are valuable for pollinators are often mistakenly identified as weeds. Native thistles (Cirsium spp.), which attract and support many pollinators, including several imperiled species of bumble bees and butterflies, are often mistaken for nonnative invasive thistle species (e.g., musk thistle [Carduus nutans], Canada thistle [Cirsium arvense]) and are sprayed with herbicides. Milkweeds (Asclepias spp.), which are host plants for monarch butterflies, are another group of plants that are targeted as weeds but do not cause problems on roadsides and rarely encroach upon adjacent lands.

Plant identification skills will help applicators know types of habitat (such as roadside prairie or wetland remnants) or stands of native plants to avoid spraying and will help to keep their applications on target. Educational materials such as booklets or posters may help. Iowa DOT and the Iowa Living Roadway Trust Fund maintain a database of native and invasive plants. Minnesota Department of Natural Resources Roadsides for Wildlife program developed a poster about invasive species in Minnesota, and many roadside managers hung the poster in maintenance sheds where it could be easily viewed. The Nebraska Weed Control Association, in cooperation with the Nebraska Department of Agriculture, put together an identification guide to help weed managers avoid treating native thistles (available at: https://neweed.org/Documents/Thistles%20of%20Nebraska.pdf).

Alternative Vegetation Control Methods

Prescribed burning, prescribed grazing, and biological control agents are additional tools in the IRVM toolbox. Though each of these tools has limitations, they may be highly effective under certain circumstances. Prescribed burns, for example, may be useful for sites with woody plant encroachment or sites where grasses have crowded out wildflowers. Prescribed grazing using goats and sheep, which can be herded and prefer to eat broadleaf plants, can control large infestations of invasive weeds and can be effective in areas near water or in inaccessible spots such as steep slopes. The use of biological control agents on roadsides can inhibit the growth of targeted weeds and reduce herbicide use, and control can be widespread and tong-term. Roadside managers can reduce impacts of these management practices to pollinators by considering the timing and intensity of the practices.

Prescribed burns can be harmful to many pollinators and have long-term impacts on the populations of some species (Ne’eman et al. 2000; Panzer 2002; Potts et al. 2005). Modifying the use of prescribed fire as a roadside management tool by timing burn events seasonally or limiting the scale and frequency of the burns will help to make this management practice more pollinator-friendly.

The timing of a burn is important with respect to its impact on the roadside plant community. Intense summer fires are most efficient at controlling woody species such as red cedar; dormant-season burns in fall or winter encourage the growth of cool season grasses. Burns at either of these times affects pollinators. Summer burns remove vegetation at a time when pollinators need floral resources, host plants, and nesting materials. Winter burns destroy species that overwinter in leaf litter or stems. Burning an entire roadside corridor runs the risk of extirpating the local pollinator community. By leaving adequate refuge habitat, enough pollinators remain to recolonize the burned areas, thereby sustaining the temporary decrease in habitat quality. Rotational burning of small sections of roadsides no more than every 3 to 5 years that leaves refuge habitat will provide the benefits of prescribed fire without causing irreparable damage to the local pollinator community (Black et al. 2011).

Grazing

Livestock grazing can directly adversely affect pollinator populations by trampling of individuals or destruction of nests, and indirectly by the removal of pollen and nectar resources, as well as host plants (Sugden 1985; Carvell 2002; Hatfield and LeBuhn 2007). Light or moderate grazing that maintains favorable vegetation heights as well as habitat heterogeneity can be favorable to some butterflies (Davies et al. 2005). For grazing to have minimal impacts on pollinators, it is important to carefully consider specialist or rare pollinators as well as the timing, intensity, and duration of grazing.

Grazing plans work best when they are site-specific and carefully timed to encourage the grazers to feed selectively on the undesirable species. For example, grazing  may only beeffective when the weed is palatable. However, managers may want to carefully time the introduction of grazers, balancing the need to control weeds with the needs of pollinators. If habitat specialist pollinator species are present, it is recommended to avoid grazing during the adult flight period or when butterfly larvae are feeding on the host plant. Additionally, grazing during periods when floral resources are already scarce (e.g., mid-summer) may result in insufficient forage for pollinators such as bumble bees, which need forage in late summer and fall (Carvell 2002).

The duration of grazing will depend on the density of grazers. If stocking density is high, the grazers will need to be on the roadside for short periods of time. Hatfield and LeBuhn (2007) found that uncontrolled sheep grazing removed enough flowering plants to eliminate bumble bees from some study sites. Generally speaking, grazing periods ideally are be short, with relatively long recovery periods for the habitat. Grazing is not right for every roadside locale, but when the grazing plan suits local conditions, it can be compatible with pollinator conservation.

Biological Control

The use of biological control on roadsides can inhibit the growth of targeted invasive weeds (e.g., leafy spurge [Euphorbia esula] and purple loosestrife [Lythrum salicaria]) and reduce herbicide use (Harper-Lore et al. 2014). Biological control of roadside weeds has the potential to benefit pollinators indirectly by reducing the use of herbicides and thus the effects on non-target vegetation. However, when biological control agents are introduced outside of their natural range to control invasive plants, there is the potential for unpredictable and irreversible ecological consequences. For example, the Eurasian weevil (Rhinocyllus conicus) was introduced to control musk thistle (Carduus nutans); however, it also feeds on native thistles, including rare thistle species (Louda et al. 1997). The loss of native thistles or other native species harms pollinators that visit the plants for pollen and nectar, such as butterflies, moths, bees, wasps, beetles, and flies, as well as butterflies that use the plants as host plants for their caterpillars.

Do not use biological control agents that have expanded their hosts to native plants, such as the Eurasian weevil. Work closely with the State Department of Natural Resources and Department of Agriculture to find the biocontrol agent that is the least disruptive. Keep careful records about release of the agents, and monitor release sites annually, monitoring not only the target weed species for population declines but also potential non-target native species (particularly those related to the target weed species). If, through inventories or monitoring, you observe that native species are being negatively impacted by biological control agents, alert partner agencies and discontinue use. If using biocontrol in large areas of monotypic stands of the target weed, ensure that there is a revegetation plan that addresses the rights-of-way and adjacent lands to prevent soil destabilization and other impacts to potential habitat.

Haying

Some States permit adjacent landowners to cut and remove the 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 (e.g., Minnesota). While not a tool utilized by roadside managers, haying does impact roadside vegetation and thus pollinators. In general, haying once in the middle of the growing season can result in high plant diversity, by favoring wildflowers and cool season grasses that are often suppressed by dominant warm-season grasses. However, too-frequent haying can reduce roadside revegetation over time (Jacobsen et al. 1990), reducing floral resources for pollinators. A poorly timed haying may have severe consequences for rare or endemic pollinator species. Although road authorities may have some restrictions in place on when and how often roadsides can be mowed (e.g., mowing only takes place once a year in August), these restrictions do not often extend to haying. States report that citizen haying might take place multiple times during a growing season. State regulations that manage the frequency and timing of haying would help to reduce the negative impacts of repeated haying on roadside vegetation and pollinators.

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Management for State-Listed, Federally-Listed, Rare, Endemic, and/or Sensitive and Declining Species of Pollinators

Species that are federally-listed as threatened or endangered are regulated by the U.S. Fish and Wildlife Service (USFWS). States also have State-listed special status species that are usually regulated by State agencies such as Departments of Wildlife. Management of vegetation that may impact habitat of a federally-listed species may require conservation measures to avoid impacts or a permit for impacts to that species (known as incidental take) if avoidance is not possible. USFWS consults on species conservation measures and issues incidental take permits through Section 7 of the Endangered Species Act (ESA) for federal actions (projects or activities with a federal nexus), or through Section 10 of the ESA for non-federal projects or actions. If there is the potential for a State-listed or federally-listed species to be impacted, the potential effects of the project or activity should be determined by the federal action agency (for federal actions) or the project proponent (for non-federal actions) based on information provided by a qualified biologist. The USFWS and/or State Department of Wildlife should be consulted if actions are likely to adversely affect one or more listed species.

Management for rare, endemic, or declining pollinator species can also generally benefit other pollinators, as well as other plants and animals. Additionally, seasonal avoidance for listed species other than pollinators, such as ground nesting birds, can benefit pollinators when the seasonal avoidance for a listed species coincides with habitat requirements of pollinators. In some cases, pollinator habitat requirements may extend slightly beyond the seasonal avoidance window for other species. In States where DOTs are already carefully timing and reducing mowing or other roadside management practices to avoid listed species, understanding pollinator needs may show that a slight extension of a seasonal avoidance may benefit pollinators as well as the listed species. 

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Summary of Recommendations for Adjusting Roadside Vegetation Management to Benefit Pollinators

Roadside Vegetation Inventories

• Use GPS and GIS to track vegetation conditions.
• Use roadside photo imagery (can be from car-mounted cameras if available) and location data to document baseline vegetation information.
• Follow driving surveys and photographic identification with ground truthing field surveys when possible.
• Identify remnant habitat and prioritize vegetation management in those areas to maintain and expand native vegetation.
• Inventory nonnative, invasive, and exotic vegetation to target them for control.
• Use online resources and technology such as smartphone apps to help identify and record vegetation information.
• Prioritize areas of high likelihood for successful pollinator-friendly plantings.

Pollinators and IRVM

• Develop IRVM plans, tailoring management to specific site conditions.
• Mow roadside vegetation as little as possible – no more than twice per year.
• Time mowing to minimize disruption to the life cycles of pollinators, especially State-listed, federally-listed, rare, endemic, sensitive, and declining species of pollinators.
• Delay mowing until the fall, preferably after first frost, to benefit a variety of pollinators by allowing flowering plants to bloom uninterrupted throughout the growing season and by reducing the risk of mortality by mower to larval stages of butterflies, moths, flower flies, and other pollinators that reside on vegetation.
• Reduce herbicide use and subsequent impacts of herbicides on pollinators by using selective herbicides, spot-spray applications, and timing applications to the most vulnerable life stage of the weed.
• Provide vegetation maintenance crews with plant identification tools and training to recognize native plants as well as invasive weeds, to reduce unintended damage to non-target plants during herbicide use.
• If sheep or goats are used to graze invasive weeds on roadsides, take into account the timing of the life cycles of rare, endemic, sensitive, and declining species of pollinators.
• If prescribed burns are used, use rotational burning of no more than every 3 to 5 years to allow time for pollinator populations and their habitats to recover.
• If biological control agents are used to control weeds, use only those agents that have not demonstrated plant host expansion beyond the target weed.
• If haying occurs in your State, limit it to once a growing season and restrict it in areas that support rare and declining pollinator species.
• Specific conservation measures are needed to protect State or federally-listed pollinator species, but these measures may also generally benefit pollinators.

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Chapter 5 - Using Native Plants to Restore Roadsides for Pollinators

Overview

Vegetation used in roadside plantings may achieve multiple goals, including safety, function, and aesthetics. Additionally, the plants are ideal when they are able to thrive in the highly disturbed, compacted, and nutrient-poor soil that remains following road construction. There are many native plants that can meet these objectives while also providing valuable resources for pollinators. In contrast, maintenance of roadsides as turf grass provides few resources for pollinators (and other animals) and is costly.

When designing roadside plantings, there are several considerations that can improve the value of the planting for pollinators. These include designing mixes with a moderate to high density of wildflowers, including species that bloom sequentially so there are flowers blooming throughout the growing season, including host plants for butterflies and shrubs that can provide bee nesting material when possible, and using native plant material that is locally or regionally sourced.

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Value of Native Plants in Roadside Plantings

Establishing regionally native plants on roadsides can help roadside managers achieve management goals such as soil stabilization and preventing storm water runoff (Cramer 1991; Quales 2003). Adapted to local conditions, native plants are better equipped than nonnative species to survive droughts and require fewer inputs like fertilizer and water during establishment. Due to strong root development (Figure 5-1), stands of native vegetation can provide effective erosion control (Quales 2003). Additionally, some species are particularly able to tolerate the poor growing conditions found on roadsides (Harper-Lore and Wilson 2000; O’Dell et al. 2007). Under some conditions, native plants may have a competitive advantage over nonnatives. Native seed mixes in a Texas study resulted in faster and denser ground cover established in roadsides than a mix with a nonnative species selected for its rapid establishment and soil stabilization (Tinsley et al. 2006).

Figure 5-1. Root Systems of Native Plants - graphic showing the root systems of prairie plants

Heidi Natura, reprinted with permission from the Conservation Research Institute

An established stand of native grasses and wildflowers will also resist weed colonization (Blumenthal et al. 2005; Falk et al. 2013). The root systems of native plants also help to reduce runoff in the spring and improve infiltration; this helps reduce storm water contamination and replenishes groundwater (Bugg et al. 1997; Harrison 2014). In northern States, native grasses and shrubs can act as snow fences in the winter, trapping and preventing snow from blowing across roads (Johnson 2000).

Although the establishment of native vegetation can take time and the initial costs may be higher, native plants are more cost effective in the long term. Once established, the plantings persist over time and require less mowing, herbicides, and other weed control measures, decreasing long-term maintenance efforts and cost (O’Dell et al. 2007; Harper-Lore et al. 2014). In contrast, controlling the growth and spread of invasive plants along roadsides through repeated mowing and rigorous herbicide use is very expensive (Westbrooks 1998).

In 1987, the Department of Public Works in Massachusetts managed roadsides at a cost of about $1.1 million, or $330 per acre; if every acre was instead managed as wildflowers, nearly $280 per acre per year could be saved (Ahern et al. 1992). Costs of installing and maintaining native vegetation will vary from site to site, depending on factors such as weed pressure. In California’s Yolo County, Robins et al. (2001) estimated roadside native vegetation installation costs, which included earthwork, tillage, herbicide, and seeding, at $522 to $1,433 per acre of roadside. They estimated maintenance costs for each of the first 3 years of establishment at $52 to $153 per acre, with similar costs occurring subsequently every 2 to 3 years.

Wildflowers and native plants have a natural beauty that can be a useful promotional tool, for DOTs as well as for tourism. Drivers form perceptions about regions based on their views of the highway landscape. Minnesota DOT conducted a study to learn more about landscape maintenance and characteristics attractive to travelers, and found that they preferred roadsides with perennial wildflower plantings or shrubs (Carmelita Nelson, pers. comm.). Over 90% of survey respondents in Mississippi preferred "natural-looking roadsides with native grasses, wildflowers, and butterflies," (Guyton et al. 2014). Stands of native grasses and flowers are aesthetically attractive and can be designed for season-long blooms. Native plantings can showcase a region’s natural beauty and provide a sense of place, natural heritage, and opportunities for education.

Native plants can fulfill all these functional roles while also supporting pollinators (See Table 5-1 for examples). In fact, native plants support more wildlife, including pollinators, than do nonnative plants (Tallamy and Shropshire 2009; Williams et al. 2011 ). Roadsides with native wildflowers support a greater number of individuals and species of butterflies and bees compared with those dominated by nonnative grass and flowers (Ries et al. 2001; Hopwood 2008). For honey bees, many native wildflowers serve as important nectar plants for honey production and can also support immune system health by providing diverse sources of pollen. For more information about plants that are beneficial to pollinators, see additional resources listed in Chapter 7.

Although introduced species with wide ranges of tolerances are competitive and can establish quickly at low cost, they are also more likely to move beyond roadside plantings. Crown vetch (Securigera varia), sweet clover (Melilotus spp.), sericea lespedeza (Lespedeza cuneata), reed canary grass, and smooth brome (Bromus inermis) are just a few examples of introduced plants that have been used for roadside revegetation and became weed problems elsewhere (Harper-Lore and Wilson 2000). In contrast, native grasses and flowers on roadsides rarely become weed issues (Harper-Lore and Wilson 2000).

Many native plants can take time to establish. During the early stages of growth, some perennial species have difficulty competing with invasive weeds. If immediate growth is needed, consider including a sterile wheat grass or a cool season nurse crop such as oats that can establish quickly and provide erosion control and weed suppression while native perennials are establishing. Annual and biennial wildflowers can also be included, so that there are blooms in the first and second years of the planting in the interim before the longer-lived perennials begin to bloom.

Different plant groups provide different functional roles and benefits. A comprehensive seed mix includes species that can occupy different niches, such as annual forbs, perennial forbs with taproots, bunch grass, and rhizomatous grass. The resulting plant communities will be better able to prevent erosion, resist weeds, be aesthetically pleasing, and contribute to a healthy environment. Cool season grasses green up early in the spring and can provide erosion control from late winter into early summer, while warm season grasses provide erosion control as they grow through the warm summer months and into the fall. Legumes can fix nitrogen and improve soil health. Native species that can establish quickly, such as black-eyed Susans (Rudbeckia hirta), can provide attractive vegetative cover, erosion control, and food for pollinators and birds while other more slow growing species establish.

Some additional criteria to consider when developing plant lists for roadsides and pollinator health include:

• Include wildflowers or shrubs with known value to pollinators and other wildlife such as songbirds or game birds. Include species that bloom in spring, species that bloom in summer, and species that bloom in fall.
• Taller herbaceous plants should be avoided in areas where lines of sight could be blocked, such as intersections.
• Reduce large herbivores like deer by avoiding known palatable species, especially if deer food sources are low at certain times of the year when the plants are most palatable. For example, consider avoiding using cool season legumes (e.g., white clover [Trifolium repens]) in erosion control seed mixtures, because these plants are forage for deer through the fall and early spring, a time when other plants for deer are scarce.
• In northern States, species to be planted close to the road it is ideal that they have some level of salt tolerance to reduce damage from road salt applications.
• Include species adapted for the soil conditions present at the roadside site (e.g., use moisture-tolerating species for wet ditches), or, if seed mixes cannot be context-specific, include species adapted to a wide range of growing conditions.
• Focus on wildflowers that establish easily and are relatively inexpensive, but include some species that are harder to establish and may be a bit more expensive to increase the aesthetics of the planting and the value of the habitat.

When installing native plant materials, consider the season in which the materials are installed. If installing plants, the best planting windows are in early spring when there is adequate soil moisture or in the fall when dormant plants can be installed. Planting during the summer can stress transplants and will reduce establishment, unless irrigation is available and the plants are handled with care. The window to install seeds varies by site and temperature and moisture levels, but is generally best in the fall or in the dormant season to aid the establishment of species that require an extended period of stratification in order to germinate. If seed mixes do not include species that need stratification, sowing seeds in spring or summer allows seeds to germinate and establish before winter. See Steinfeld et al. (2007) for more information.

Additional obstacles to widespread use of native plants on roadsides include the cost of native plant material and limited availability of locally native plant material in some regions, as well as a lack of expertise with native plant establishment (see Chapter 6 for more information). Despite these obstacles, native plants are effective tools that roadside managers can use to stabilize roadsides, while also supporting pollinators and overall ecosystem health.

Table 5-1. Examples of Native Plant Species Suitable for Use in Roadside Revegetation and Examples of the Ecosystem Services they Provide

Name	Regional Distribution	Type of Plant	Examples of Functional Roles/ Ecosystem Services
Canada wild rye (Elymus Canadensis)	Northeast, Midwest, Great Plains, Intermountain west, Southwest	Cool season grass	Establishes quickly Erosion control Cover in early spring-summer Cover and nest material for birds Host plant for a skipper species
Western wheatgrass (Pascopyrum smithii)	Across West, Southwest, Great Plains, Midwest, extending to Texas, Kentucky, and Michigan	Cool season grass	Erosion control Cover in early spring-summer Nesting material for birds
Sedges (Carex spp.)	Across the U.S.	Cool season plants	Erosion control Cover in early spring-summer Many tolerate moist soils Nesting material for birds Host plants for skippers and moths
Bluejoint grass (Calamagrostis canadensis)	Northeast south to North Carolina, extending west to Washington and California	Cool season grass	Establishes quickly Erosion control in wet areas Nesting material for birds Cover for small animals
Little bluestem (Schizachyrium scoparium)	Maine south to Florida, extending west to Idaho and Arizona	Warm season grass	Provides long-term erosion control Host plant for many skippers Food for birds Structure for bumble bee nests
Side oats grama (Bouteloua curtipendula)	Present throughout U.S. except the Pacific northwest	Warm season grass	Long-term erosion control Bird nesting habitat and cover Food for birds Host plant for skippers
Tall dropseed (Sporobolus compositus)	Present in much of the U.S. except Florida, California, Nevada, and Oregon	Warm season grass	Establishes quickly Erosion control Food for birds Bird nest habitat Structure for bumble bee nests
Golden alexanders (Zizia aurea)	Eastern U.S., extends west to Great Plains	Wildflower	Spring bloom Food for pollinators Host plant for swallowtail butterflies
Silverleaf phacelia (Phacelia hastata)	West coast to western Great Plains	Wildflower	Spring bloom Food for pollinators
Firecracker penstemon (Penstemon eatonii)	Western U.S.	Wildflower	Spring bloom Very showy Food for pollinators
Lead plant (Amorpha canescens)	Michigan south to Louisiana, west to New Mexico and Montana	Wildflower, legume	Fixes nitrogen-improves soil quality Early summer bloom Food for pollinators Food for birds
Wild bergamot (Monarda fistulosa)	Extends across the continental U.S. except California and Florida	Wildflower	Establishes quickly Early summer bloom Food for pollinators
Showy milkweed (Asclepias speciosa)	Extends from Great Lakes region south to Texas and west to Pacific coast	Wildflower	Early summer bloom Very showy Food for pollinators Monarch butterfly host plant
Black-eyed Susan (Rudbeckia hirta)	Throughout the U.S.	Wildflower	Establishes quickly Summer bloom Food for pollinators Food for birds Host plant for butterflies
Partridge pea (Chamaecrista fasiculata)	Eastern U.S. and Great Plains	Wildflower, legume	Fixes nitrogen-improves soil quality Establishes quickly Summer bloom Pollinator food Food for birds, small mammals Host plant for butterflies
Blanketflower (Gaillardia aristata)	Western U.S. into the Great Lakes region	Wildflower	Summer bloom Very showy Food for pollinators Food for birds
Purple coneflower (Echinecea purpurea)	Eastern U.S. into the Great plains	Wildflower	Summer bloom Very showy Food for pollinators Food for birds
Swamp milkweed (Asclepias incarnata)	Extends across Eastern U.S. to Idaho and Arizona	Wildflower	Adapted to moist/wet soils Summer bloom Food for pollinators Monarch butterfly host plant
Sulfur buckwheat (Eriogonum umbellatum)	Western U.S.	Wildflower	Summer bloom Food for pollinators Food for birds Butterfly host plant
Blazing star (Liatris punctata)	Michigan south to Louisiana, west to New Mexico and Montana	Wildflower	Adapted to moist soils Summer bloom Very showy Food for pollinators Food for birds
Lavender hyssop (Agastache foeniculum)	North central U.S., from Montana to Great Lakes and south to Colorado and Kentucky	Wildflower	Establishes quickly Late summer bloom Food for pollinators Food for birds
Mist flower (Conoclinium coelestinum)	Eastern U.S. into southern Great Plains	Wildflower	Adapted to moist/wet soils Late summer bloom Food for pollinators Food for birds
Maximilian sunflower (Helianthus maximiliani)	Present across most of the U.S. except the Southeast	Wildflower	Establishes quickly Fall bloom Food for pollinators Food for birds Butterfly host plant
Showy goldenrod (Solidago speciosa)	Eastern U.S. and Great Plains	Wildflower	Fall bloom Food for pollinators Food for birds
Western goldentop (Euthamia occidentalis)	Western U.S.	Wildflower	Adapted to wet/moist soils Fall bloom Food for pollinators
New England aster (Symphyotrichum novae-angliae)	Northeastern U.S. south to Georgia, extending across much of the West	Wildflower	Establishes quickly Fall bloom Food for pollinators Food for birds Butterfly host plant
False goldenaster (Heterotheca villosa)	Western U.S. into northern Great Plains and western Great Lakes region	Wildflower	Mid-summer to fall bloom Adapted to dry conditions Food for pollinators Food for birds

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Using Native Plants in Roadside Plantings to Benefit Pollinators

Improving the quality of roadside habitat can increase the number and diversity of pollinators, and may increase pollination services as a consequence. There are two main goals when restoring habitat for pollinators: 1) increase the abundance of pollen, nectar, and host-plant resources with use of a diverse range of plants that flower throughout the growing season, and 2) foster vegetation that provides nesting, egg-laying, and overwintering locations for pollinators. Roadside habitat restoration can take the form of wildflower plantings, inter-seeding low-statured pollinator-attractive plants in existing grassy areas, and establishing flowering shrubs and trees in living snow fences, windbreaks, or slope stabilization efforts.

Bees and butterflies are more abundant and diverse on roadsides with native plants compared with those dominated by nonnative grass and flowers (Ries et al. 2001; Hopwood 2008). In addition to the use of native plants, key components of roadside plantings that will benefit pollinators include a focus on high diversity and density of flowering species, selecting plants that provide pollen and nectar, plants that are host plants for butterflies and moths, plants that provide nesting and shelter for pollinators, and prioritizing the use of species found in the project’s ecoregion.

Plant Diversity and Density

Diverse plant communities provide higher habitat value for pollinators. For example, bee diversity increases with increasing flowering plant diversity (Potts et al. 2003). Diverse plantings that resemble natural native plant communities are also the most likely to resist pests, disease, and weed invasions (Tilman et al. 2006; Oakley and Knox 2013) and thus confer the most benefits to DOTs and pollinators over time.

Ideally, seed mixes have an even grass to forb ratio. Although it is more affordable to increase the amount of grass in mixes than to increase wildflowers, if grass density is too high, or if mixes include a large percentage of a dominate grass species (e.g., big bluestem [Andropogon gerardii]), grasses can outcompete and suppress wildflower abundance over time. To achieve high plant diversity and long-term stability of a stand of vegetation intended for erosion control, a minimum of 25% of the seed mix are wildflowers, but 50% results in a considerably more diverse planting. In highly visible areas, seed mixes for showy plantings are best when they include greater than 50% wildflower component. Whenever the site characteristics and project budget can accommodate it, increasing wildflowers is ideal.

Plant Selection

Pollinator Attractiveness and Bloom Time

It is important that flowers are available to pollinators throughout the entire growing season. Early-season pollen and nectar sources may lead to greater reproduction of bees by encouraging bees that are emerging from hibernation to start their nests nearby or increasing the success rate of nearby nests. Late season flowers provide resources that ensure that queen bumble bees have ample food going into winter hibernation, and that honey bee colonies have enough food stores to last through the winter.

Focus on selecting plants known to provide quality forage to pollinators. See Pollinator Plant Recommendations in Chapter 7. To encourage the greatest number and diversity of pollinators, include a diversity of plants with different flower colors, sizes, and shapes as well as varying plant heights and growth habits. Bees typically visit flowers that are purple, violet, yellow, white, and blue (Procter et al. 1996). Butterflies visit a similarly wide range of colors, including red, whereas flies are primarily attracted to white and yellow flowers (Procter et al. 1996). Thus, by having several plant species flowering at once, as well as a sequence of plants flowering through spring, summer, and fall, restored habitat can support a wide range of pollinator species that fly at different times of the season. Additionally, diverse plantings provide greater diversity of pollen and nectar sources for honey bees. Diversity in diet can help support honey bee immune system health (Alaux et al. 2010; Di Pasquale et al. 2013 ).

Host Plants for Butterflies and Moths

Egg-laying sites for butterflies and moths consist of plants upon which the adult will lay eggs and the larvae will feed after hatching. Roadsides with host plants can support habitat generalist butterflies as well as habitat specialists and migrant species such as the monarch butterfly (Ries et al. 2001). Some butterflies may rely on plants of a single species or genus for host plants (the monarch butterfly is an example, with caterpillars feeding only on species of milkweed [Asclepias spp.]). Others may exploit a wide range of plants, such as some swallowtails (Papilio spp.), the larvae of which can feed on a range of trees, shrubs, and wildflowers. Given this lifecycle pattern, establishing caterpillar host plants is recognized as a way to sustain butterfly populations (Croxton et al. 2005; Feber et al. 1996). Many plants already used in erosion control native plant species mixes are butterfly and moth host plants, but it may be necessary to include additional species to support certain butterflies or moths. For example, planting milkweeds will contribute to the recovery of the monarch butterfly.

Nesting, Shelter, Overwintering Habitat

Grasses and sedges often provide food or shelter resources for pollinators (see Table 3-1 for pollinator habitat needs), serving as larval host plants for some butterflies, potential nesting sites for colonies of bumble bees, and possible overwintering sites for various beetles (Kearns and Thompson 2001; Collins et al. 2003). Tall vegetation can provide shelter for adult butterflies and moths, as well as other pollinators such as flower flies. Most of North America’s native bee species (about 70%) nest in the soil and need access to soil surfaces between vegetation to excavate and access their nests (Michener 2007). Bunch grasses tend to provide better nesting habitat than sod-forming grass species, and roadsides with native bunch grasses have more nesting opportunities for ground-nesting bees and, consequently, a greater abundance of ground-nesting bees (Hopwood 2008).

Other native bees nest in tunnels in wood, such as abandoned beetle tunnels in logs, stumps, and snags, or excavations in the centers of woody plant stems and twigs (Michener 2007). Where site appropriate, planting native wildflowers with pithy stems, such as cupplant (Silphium perfoliatum), ironweeds (Vernonia spp.) and sunflowers (Helianthus spp.), along with shrubs such as wild rose (Rosa spp.), elderberry (Sambucus spp.), sumac (Rhus spp.), or agave (Agave spp.), will provide resources for stem-nesting bees.

Sourcing Native Plant Material

The source of the plant material can have implications for the quality of the restoration and quality of pollinator habitat. Where available and economical, native plants and seed are best when procured from local ecotype providers. Local ecotype plant materials that originated in geographic proximity to the project site will generally establish and grow well because they are adapted to the local climatic conditions (Lippit et al. 1994). Plant material of native species that originated from an area where the climate, moisture, soil, and pest pressures differ may be less adapted for local conditions and may not establish. Alternatively, they could establish to such an extent that they become problematic. The phenology of non-locally sourced seed can also differ (Norcini et al. 2001; Houseal and Smith 2000; Gustafson et al. 2005). Bloom times of non-locally sourced plants have the potential to be out of sync with pollinators, especially specialist pollinators that are reliant on the pollen from a small subset of plants and time their emergence annually with the bloom time of their host plants.

The use of cultivars in roadside plantings can diminish nearby remnant habitat by introducing new diseases or contaminating gene pools (Houseal and Smith 2000). Additionally, some cultivars have been bred for a particular trait such as showiness and may have little to no pollen and nectar and therefore little value to pollinators.

Although the use of locally native seed and plant material sources is an ideal, where such sources are not available, regional designations may be an acceptable way of sourcing plant material.

Compatibility with Highway Safety

Vegetation management is a key component of highway safety (Federal Highway Administration 2008). The American Association of State Highway and Transportation Official’s Highway Safety Manual has data showing that widening the paved shoulder area may reduce the potential for crashes. Landscape plantings as well as revegetation efforts are designed to adhere to standards governing setbacks, visibility, and other safety concerns. For many roadside managers, the biggest concerns about the presence of taller native vegetation along roads are sight distance and reducing the potential for collisions with large herbivorous mammals like white-tailed deer.

Native plants beneficial to pollinators can be included in roadside plantings without compromising highway safety. Potential adjustments include:

• Maintaining a regularly mown clear zone, the vegetation adjacent to the pavement. A regularly mown clear zone can increase sight distance and reduce deer-vehicle collisions (Mastro et al. 2008). Though nonnative grasses are typically planted in that zone, there are several native grass species that can be maintained as turfgrass, including buffalo grass (Bouteloua dactyloides), blue grama (Bouteloua gracilis), and curly mesquite (Hilaria berlangeri) (Simmons et al. 2011).
• Where regionally appropriate, install living snow fences to reduce ice and drifting snow. Living snow fences composed of shrub species that provide pollinator forage, host plants, or nesting material can provide multiple ecosystem services while maintaining sight distance.
• Use native grasses, herbaceous perennials, and small shrubs for the clear zone, the zone of vegetation that remains clear of fixed objects (such as trees).
• Avoid tall grasses (e.g., Indiangrass [Sorghastrum nutans]) and tall wildflowers (e.g., cupplant [Silphium perfoliatum]) in high crash zones, and within the lines of sight at intersections and around curves.
• Modify the behavior of large herbivores like deer by making the roadside less attractive for foraging. Avoid planting known palatable species, especially if deer food sources are low at certain times of the year when the roadside plants would be most palatable. Arizona DOT’s approach has been to plant unpalatable species near the shoulder of roads and in high crash areas, and plant palatable species in areas leading to designated bridged wildlife crossing or in the habitat adjacent to the roadside rights-of-way (Brown et al. 1999).
• Reduced mowing beyond the clear zone may also decrease deer foraging because mowing can increase the palatability of some plants (Mastro et al. 2008).

The presence of native wildflowers and grasses on roadsides may actually increase highway safety. Research indicates that non-turf roadside vegetation provide aesthetic variety and break up monotony (Billings 1990) and can have a positive effect on human performance and improve highway safety (Topp 1990 ; Cackowsky and Nasar 2003 ; Mok et al. 2006). Anecdotal evidence backs it up as well: the Federal Highway Administration (FHWA) once received a handwritten letter from a truck driver thanking them for all of the wildflowers along the road, to which he credited with keeping him awake throughout his long drives. In urban settings, where State DOTs report that citizens have a lower tolerance for non-turf vegetation, studies show that highways with natural vegetation contributed to clearer thinking (Macdonald et al. 2008). In Mississippi, public perception surveys found strong support for wildflowers on roadsides and reduced mowing, and respondents indicated they would tolerate a less manicured roadside if it made the roads safer (Guyton et al. 2014).

Prioritizing New Plantings for Pollinators

Prioritizing roadside sites for restoration can help to maximize restoration success, use limited resources effectively, and garner public approval. There are several considerations to help prioritize projects that establish native plants on roadsides (including landscape plantings and revegetation for erosion control). Restoration experts suggested selecting sites for pollinator-friendly plantings with care, working with restoration experts to build internal DOT restoration experience, and conducting public outreach.

Successful establishment, persistence, and public perception of roadside plantings to benefit pollinators can depend on site selection. Roadside sites that are unlikely to undergo construction within 10-15 years might be prioritized for revegetation or pollinator-friendly landscape projects over other sites to ensure the long-term persistence of the plantings and to protect the investments of cost and time. Efforts focused on the widest roadsides will maximize potential habitat for pollinators. Butterflies in particular appear to prefer wider roadsides (Munguira and Thomas 1992; Saarinen et al. 2005).

Feasibility of restoration is also important to consider during site selection. Efforts may  first be aimed at areas with low weed pressure before restoring other areas. In areas with high weed pressure, native plant establishment can mean more time, expense, and restoration expertise. DOTs that have limited experience with native plant revegetation may want to begin their efforts by starting with small-scale projects. Experience gained from smaller test areas can then be applied to larger projects. Working with local partners or experts to augment restoration expertise is also recommended.

Selection of sites may also take into account surrounding land use. Placing a site in the wrong location in the landscape can lead to a loss of the investment in the plant material and staff time for the restoration and may affect public approval. Even worse, poorly sited projects can become a sink for pollinators and other wildlife, where the animals are drawn into the habitat but are a subsequently killed by insecticide drift or too much mowing, haying, or herbicide use at the site. 

Native plants established on roadsides can be subject to accidental disturbances from adjacent land management (e.g., pesticide drift) or intentional disturbances (e.g., excessive haying, mowing, or herbicide applications to the roadside by adjacent landowners). Off-target herbicide applications can damage roadside plantings, which can reduce the habitat quality for pollinators and other wildlife and also increase opportunities for weeds to invade the planting, further decreasing its quality. This type of damage can occur in roadsides adjacent to herbicide-resistant crops when boom sprayers are not turned off as sprayers turn around at the edges of fields in the process of applying herbicides.

Insecticide drift onto roadsides can also occur if applications are made to crops under improper weather conditions, if equipment isn’t calibrated properly, or when dust sloughs off of insecticide-treated seeds during crop planting and drifts onto roadside plants. Intentional herbicide applications, or excessive mowing or haying of the roadside by the adjacent landowner, can also decrease the quality of habitat. If using native plants, high quality seed mixes or plant materials are often involved in the establishment process. Sites could be located to protect these investments as much as possible. Plantings could be located next to places where the adjacent landowner will not impact habitat quality, such as rest areas, parks, public areas, churches, organic farms, or if adjacent landowners are aware of the value of protecting the habitat, next to farms or businesses.

If a project goal is to highlight the value of DOT rights-of-way, sites planted with showy wildflowers to benefit pollinators are ideal when located in areas that are visible to the public, such as rest areas, or sites near farms that could benefit from the pollination services the roadside habitat would help to support (e.g., roadside sites near almond orchards in California). Public education and perception of the planting is important and can influence the persistence of the planting. Visible plantings may make surrounding landowners more aware of the importance of roadside habitat, which may decrease landowner spraying, mowing, or haying of the roadside.

Visible plantings are one component of community outreach. Signage, either on roadsides or at rest areas, can also inform the public. Community meetings might also be a useful tool for obtaining by-in from local citizens, as can making information about the plants themselves available online through a DOT’s website.

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Summary of Recommendations for Using Native Plants in Roadsides to Benefit Pollinators

• Prioritize the use of native plants in erosion control and landscape projects.
• Increase the diversity and abundance of native flowers on roadsides, especially flowering plants that benefit pollinators. Seed mixes for erosion control projects are ideal when they have 50% wildflower component, and landscape projects are ideal when they have higher densities of flowering plants.
• Select flowering species that have sequential and overlapping bloom times to provide resources for pollinators throughout the growing season.
• Include plant species known to provide quality forage to pollinators or nesting materials.
• Include butterfly and moth host plants (e.g., milkweeds for monarch butterflies).
• Prioritize the use of locally sourced plant material, which can improve establishment and persistence of plantings, as well as the value to pollinators.
• Avoid compromising highway safety by maintaining a strip of vegetation adjacent to the pavement that is mown regularly, avoiding tall plants in high crash zones and within lines of sight, avoiding planting species that are palatable to deer, and installing living snow fences to help reduce drifting snow.
• Prioritize sites for new high quality roadside restorations to maximize restoration success and use resources effectively. Select roadside sites that have low to moderate weed pressure, are wide, are not going to be subject to construction, and will not be impacted by adjacent land use such as pesticide drift.
• By starting with small projects and forming partnerships with restoration experts in State agencies or local conservation organizations, DOTs with limited restoration experience can develop internal expertise and expand by building off of successful projects.

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Chapter 6 - Overcoming Obstacles to Implementing Pollinator-Friendly Practices

In order to better understand existing roadside vegetation management practices and how they relate to pollinator conservation, we interviewed State DOT representatives and roadside restoration experts. The interviews revealed challenges to implementing roadside vegetation management strategies that can benefit pollinators, as well as ideas about tools and resources to mitigate challenges to implementation.

Reducing Mowing

Several transportation agency personnel and restoration experts interviewed were of the opinion that some State DOTs are not open to simple changes like reduced mowing. Reasons cited include a culture within the agency that prefers the status quo, a lack of knowledge about the benefits of reduced mowing, and misinformation about the effects of reduced mowing on vegetation and erosion control. As an example of barriers to reducing mowing, one State representative pointed out that roadside mowing guidelines have been guided by the turf management program at local universities.

Internal support for adoption of reduced mowing practices can be built by learning from the experiences of other nearby State DOTs. States that have successfully implemented reduced mowing can serve as examples and as technical resources for other States. Internal support can also be increased by making small changes and observing results. Florida DOT’s Research Center undertook a research project that piloted a reduced mowing regime along a highway. The study followed the changes in vegetation that resulted from reduced roadside mowing beyond the clear zone, monitored soil erosion, and tracked costs (Norcini 2014 ). When results revealed that reduced mowing did not impact soil erosion, but did reduce maintenance costs and improved aesthetics by allowing wildflowers to bloom, the agency became more open to the possibility of reducing mowing across the State.

State DOTs also expressed concern about how the general public might view reduced mowing. Particularly in urban areas, where unmown grassy roadsides are more likely to be viewed as "messy," there is pressure to maintain roadsides through frequent mowing. However, the findings of several DOT surveys suggest that mown turf roadsides are not the only favorable option. In Minnesota, a survey found that travelers prefer wildflowers or shrubs over a manicured turf (Carmelita Nelson, pers. comm.). In Delaware, survey respondents rated an unmown roadside with a mowed edge as attractive as a fully mowed turf roadside (Barton et al. 2009).  By only mowing the strip of roadside adjacent to the pavement and allowing the rest of the vegetation to grow as a meadow, States can reduce costs and the roadside will remain attractive.

Public opinion around reduced mowing can be improved by outreach efforts. Public education is an important component of maintenance programs. Education about the economic benefits as well as the ecological benefits will help to make reduced mowing palatable to the public. Web resources, posters, brochures, signage on roadsides and at rest areas, community meetings, or news articles are all possible avenues for education. States can also develop partnerships with other State agencies (e.g., Departments of Natural Resources or Fish and Game) or organizations such as native plant societies or land management groups to leverage their resources to gain community support by reaching varied audiences. The presence of colorful wildflowers can also be a tremendous boost to public relations.

Obstacles

• There may be internal resistance to reducing mowing, due to a culture within DOTs that have a long history of managing vegetation as turf or where misinformation about purported negative effects of reduced mowing prevail.
• Some members of the general public may be resistant to the idea of reduced mowing, viewing unmown roadside vegetation as less attractive than roadsides managed as turf.

Possible Solutions

• Education and training about the long-term cost savings and economic and ecological value of reduced mowing to administrators, State engineers, resident engineers, and district engineers may help increase the comfort level within the transportation agency.
• Implement pilot projects to test reduced mowing regimes on a small scale before adopting widely.
• Communicate with other nearby State DOTs that have implemented reduced mowing regimes and exchange information.
• Community outreach and education, using economic as well as environmental arguments to support the maintenance changes can help to bring the public on board with reduced mowing regimes. Public education opportunities such as signs on roadsides and at rest areas, web resources, and brochures are some ways to spread the word out about the benefits of natural native wildflower habitat.
• Maintain a regularly mown clear zone adjacent to the pavement.
• Aesthetically pleasing native roadside plantings, which often require less mowing, can also increase public support.

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Reducing Herbicide Use

Limited resources for training were identified as a constraint to reducing herbicide use. Very few of the States we interviewed provide their maintenance staff with training to identify native vegetation. As a consequence, maintenance staff cannot always recognize the difference between an invasive species such as an introduced thistle and a beneficial native wildflower such as blazing star (Liatris spp.). Training to recognize common native plants, as well as noxious and invasive weeds, is needed. Ideally, hands-on training would be conducted in the field, but pocket guides that can be stowed in trucks or tractors, and posters hung in maintenance shops would also be useful. Annual training to support best practices of herbicide use, such as timing applications effectively and using the most efficient equipment available, is an indispensable component of herbicide reduction programs.

Constraints of staff time and resources during busy periods of the season result in applications of herbicides made at non-optimal times, according to States that already make a conscious effort to time applications of herbicides to be most effective. It is recommended that States in this situation do their best to time applications, but at a minimum, treat weeds before the flowering stage.

Obstacles

• Few members of the maintenance staff have the training to recognize native plants, and those who don’t have training spray beneficial native plants as well as invasive species.
• Herbicide applications are not always timed effectively due to constraints on maintenance staff time and resources.

Possible Solutions

• Provide training to increase plant identification skills so staff can recognize native plants as well as invasive weeds. If expertise to train staff does not exist within the agency, consider ways to partner with other State agencies or universities to develop a training program. Hold training at least once a year to ensure staff stays informed about any new developments in the vegetation management field. Field identification guides are also helpful tools.
• Establish protocols to time applications as effectively as possible within the given operational constraints of the agency.

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Conducting Roadside Vegetation Surveys

The preservation of native plant communities is important for the health of ecosystems as well as for the natural heritage of an area. Identification of native plant communities and locations with invasive species along roadsides is the first step to effective roadside management. If maintenance staff does not currently have the expertise to conduct surveys, there are many public agencies or private organizations that would likely be willing to partner to the mutual benefit of all involved.

Obstacles

• Few DOTs may have internal botanical expertise to conduct roadside vegetation surveys.

Possible Solutions

• Partner with local botanical experts, State agencies, and/or universities to conduct roadside surveys with maintenance staff.

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Using Alternative Vegetation Management Tools

Prescribed burns and targeted grazing can be cost-effective and efficient tools for aiding native plant establishment, controlling invasive plants, and managing vegetation over time on roadsides. However, these tools are not used very frequently, even under circumstances for which they might be the most appropriate management tools because of concerns over compromising motorist safety. Prescribed burns and grazing can be executed on some roadsides without endangering motorists or adjacent land. Careful planning to control traffic during a burn or to fence in grazers and proper staff training are needed, however. DOTs can partner with State land management agencies or local conservation organizations to gain training and expertise to conduct prescribed burns or prescribed grazing regimes on appropriate roadside sites.

Obstacles

• Use of prescribed burns and grazing for managing roadsides is limited, though both are effective vegetation management tools and can be valuable for revitalizing roadside plant communities.

Possible Solutions

• Collaborate with State agencies or local conservation organizations to gain training from experienced experts and to implement grazing and prescribed burns.

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Obtaining Plant Materials

Increasing the use of native plants in roadside plantings is a key component of managing roadsides to benefit pollinators. Availability of regionally-sourced plant material is a constraint for some States. For example, there are few native seed vendors in Idaho, which limits the plant species that can be used in roadside plantings as well as the scale of plantings. A State may have a number of native species they would like to use for projects but that are not available in sufficient quantities. As a consequence, a DOT may only be able to work with a limited subset of native wildflowers. In practice this could result in mixes that are very costly, have a limited range in bloom times, or do not include key host plants for butterflies.

Cost is also an obstacle that is closely tied to issues of availability of native plant material. In some cases, seed can cost over $100 per ounce for certain species of native wildflowers, including species that would otherwise be ideal to include in roadside projects because they establish quickly, contribute to erosion control, fix nitrogen, or support pollinators. But seed for these species are currently typically too expensive for routine use.
There are a number of possible approaches for increasing the availability of regionally sourced seed and transplants. In regions of the country where there is not a developed native seed industry, private nurseries and agencies may to cooperate in pilot projects to develop an industry. Grants, tax benefits, or other incentivized funding tools would help to expand a nascent native seed industry.

DOTs could also consider establishing their own native seed production operations. Indiana’s Hoosier Roadside Heritage Program collected seed from remnant prairie habitat in Indiana and established foundation seed plots and eventually production plots (see the Hoosier Roadside Heritage Program’s website at https://www.in.gov/indot/2583.htm- content is no longer available).

Operation Wildflower, a cooperative program between FHWA, State highway agencies, and the National Council of State Garden Clubs, might be an opportunity for some State DOTs to increase their use of native plants or obtain foundation seed for further production. The program encourages garden clubs to contribute to the use of wildflowers in roadside plantings by providing plant material for projects, though the DOT has the final say in what species are used and where they are installed. West Virginia’s Donate a Wildflower Site is a similar idea: donors make a financial contribution to support the planting of wildflowers at a particular roadside site, designated by a recognition sign. The Transportation Alternatives Program, a competitive grant for State and local organizations other than transportation agencies, is an opportunity to collaborate with transportation agencies to obtain funding and implement vegetation management projects (more information available at https://www.fhwa.dot.gov/environment/transportation_alternatives/guidance/). Several States have specialty wildflower license plates (e.g., Florida, Oklahoma, and Texas), the sales of which support wildflower plantings, research, and education.

In regions of the country where native seed industries are well developed, incentives to existing seed producers can help to increase production and availability. On a State level, State DOTs can commit to increasing the use of native plants when using federal funds. State DOTs can also commit to purchasing and planting State- or region-origin seed. By following through with purchasing regionally sourced seed, DOTs can foster a stable native seed market that will eventually lead to greater production and lower costs. An approach that worked for Arizona DOT was placing a value that was 20-30% above market value on the species they needed most. Working with native seed producers and communicating about species lists and upcoming needs helped to increase availability in Arizona.

However, some States with thriving native seed industries that can offer a large diversity of species for reasonable prices may still face internal push-back about the costs of native plants. In part, resistance to the use of native plants may be a budgetary issue, with limited resources available for roadside planting projects because of other priorities. Resistance may also arise when administrators, State engineers, resident engineers, and district engineers underestimate the long-term economic value and the ecological value of the use of native plants. Among the many duties of a DOT, land management may often be overlooked. Staff education and training can spread awareness. Commissioning additional studies and/or a report on the long term costs of native plantings versus nonnative plantings would allow DOTs to determine if the long term cost savings outweighed the short term costs.

Obstacles

• The availability of regionally sourced native plant material varies widely across regions.
• Native plant materials may cost more than nonnative plant materials.

Possible Solutions

• In regions where no native seed industry exists, private nurseries and agencies could cooperate to build an industry. Grants, tax benefits, or other incentivized funding tools would assist the process. DOTs could also consider establishing their own native seed production operations.
• In regions of the country where native seed industries are already developed, DOTs can help to increase production and availability by committing to the use of native plants, purchasing and planting State- or region-origin seed, and communicating needs to seed vendors, which would foster a stable market that will eventually lead to greater production and lower costs.

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Training Staff

Education and training were universally mentioned as indispensable by DOT employees and roadside restoration experts. In particular, the people we interviewed expressed a need for DOT staff training to support the use of native plants, including background information about the economic and ecological value of native plants, the process of establishing native plants and the long term management of native plants.

Value of Native Plants

Some State DOT personnel feel that roadside vegetation is not recognized by administrators, engineers, designers, and/or maintenance staff as an important component of the highway system. Training and education about the ecosystem services that roadsides can provide and how to restore and manage roadsides as the natural resources they are, are important for maintenance staff, design staff, engineers, and middle management of State transportation agencies. To balance ecosystem information with fiscal concerns, the potential for cost savings from practices like reduced mowing are good to highlight when discussing the benefits of pollinator-friendly practices with agency managers and leadership. Participation in trainings by other State DOTs, agencies, or local experts may help to build local connections and share expertise.

Internal support for pollinator conservation can be approached directly, citing the value of pollinators to agriculture and ecosystems and the role roadsides can play in pollinator conservation. Or an indirect approach highlighting the multiple benefits of native plant restoration, one of which is pollinator conservation, might be more effective. Managing roadsides to benefit pollinators means managing roadsides to benefit biodiversity. Internal awareness and support can increase communication between functional units within DOTs, increasing efficiency and effective roadside management.

Plant Establishment and Management

Some States express concern about the process of establishing native plants. States that lack experience and expertise with native plant establishment may need to acquire staff with restoration background. Alternatively, they can work with organizations and partners to learn from existing regional expertise, or learn from DOTs that have histories of successful implementations (examples include Arizona, California, Iowa, Nebraska, and Oregon).

Obstacles

• Within DOTs, administrators, State engineers, resident engineers, and/or district engineers may resist using native plants due to initial expense, unfamiliarity with native plants, or because competing priorities overshadow roadside vegetation management concerns.
• There is a lack of expertise in establishing native plants within many DOTs.

Possible Solutions

• Education and training about the long-term economic and ecological value of native plants in roadsides to administrators, State engineers, resident engineers, and district engineers may help increase the comfort level around the use of native plants.
• Education and training about native plants and their establishment would build expertise, as would partnerships with other State land management agencies or conservation experts.

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Native Plants, Education, and Public Relations

Effective communication with the public is an important component of roadside restoration programs. The success of roadside restoration programs can hinge on public support. Yet the general public may lack awareness of the ecological and economic values of such a program and are less tolerant of the aesthetics of roadside restorations that are less manicured than traditional turf roadsides. Native plantings can take several years to establish and reach an attractive appearance. Additionally, some adjacent farmers and ranchers see native plants as a threat to their operations. For example, milkweeds, host plants of monarch butterflies, are frequently perceived as problematic roadside plants that will become weeds on a farmer’s adjacent land. Landowners may mow down or spray out roadside wildflowers and decrease the quality of the roadside restoration. DOTs may wan to raise awareness and inform the public of the benefits of using native plants along roadsides and other sustainable roadside management practices.

Raising Public Awareness

Aesthetically, roadside restorations are a divergence from traditionally mown turf roadsides. Public awareness of the economic and ecological value of establishing and maintaining native vegetation on roadsides, including the benefits to pollinators, and the processes involved in establishing native vegetation, will help to increase public support.

General recommendations to generate public support for roadside restoration programs include spreading educational information through a number of avenues and producing effective restorations that can serve as examples of successes. Disseminate native plant information via web resources, posters, brochures, signage on roadsides and at rest areas, community meetings, or news articles. Develop a series of native plant public service announcements for local television and radio. Offer promotional items, such as license plates, wildflower handbooks, seed packets, or t-shirts that could be purchased to provide funding for the program.

Identify groups that are natural allies or that could provide support for your roadside program, such as native plant societies, local garden clubs, and tourism organizations. Reaching out and presenting to civic groups can garner support too. Partnerships with other State agencies (e.g., Departments of Natural Resources or Fish and Game) or organizations such as native plant societies or land management groups can increase audiences reached. Partnerships with other organizations that work with farmers, or extension services of universities, can help to correct misinformation about native plants while highlighting the importance and value of roadside native plants.

The presence of colorful wildflowers on roadsides, designated by signage, can be a tremendous boost to public relations and to tourism. Wildflower tourism is promoted in several States, including Texas and Florida. West Virginia DOT offers a "Roadsides in Bloom" calendar each year that includes photos of wildflowers on roadsides. WV DOT holds a photography contest to determine the photographs included, and in the process spreads awareness of roadside flowers. Plantings strategically located in visible areas or in regions where farmers will benefit from spillover ecosystem services like pollination can serve as demonstrations.

Staff Awareness

Maintenance staff, as well as any DOT staff that deal with the public, ideally would have training to understand the goals and practices of roadside restoration programs. Such training will benefit staff when they coordinate with the adjacent land owners and address any issues or concerns. Additionally, if staffers are knowledgeable about the practices, they can help to promote the advantages of the program to the public, answer questions (see page 6-11 for example language that could be used when communicating with the public about promoting wildflowers along roadsides to benefit pollinators) and resolve any complaints or problems that arise, all of which can increase public approval. Having a packet or handbook of information available to the staff may be helpful.

Resolving Complaints

Despite the financial and functional arguments for the use of native plants along roadsides, not everyone will be receptive. However, public complaints about weedy roadsides represent a small proportion of the people using the road. DOTs frequently respond to these complaints by increasing mowing, which can be detrimental to restorations. However, complaints may not be the best gauge of public perceptions; public opinion surveys may be more accurate (Guyton et al. 2014).

Obstacles

• Native plants may be perceived by the general public as weeds or a threat to neighboring land.

Possible Solutions

• Help the public to understand the ecological and economic value of using native plants to manage roadsides.
• Form partnerships with other organizations or agencies to provide education and outreach about native plants.
• Incorporate native plants into tourism campaigns and install showy plantings in visible locations.

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Final Thoughts

With thoughtful management, roadsides can provide our nation’s critical pollinators with millions of acres of much-needed habitat. Pollinators will benefit from DOTs that adjust the frequency and timing of vegetation management to augment floral resources, and from the enhancement and restoration of native vegetation to roadside habitat. Some of the obstacles to implementing these changes include skepticism about the value of reduced mowing from DOT staff and the public, the availability and cost of native plant material, and a lack of expertise with native plant identification and establishment within DOTs. In order to successfully implement roadside management regimes that benefit pollinators, State DOTs need training and tools, access to native plant materials and restoration expertise, and a plan for outreach to the public.

Beyond the value to pollinators, roadsides managed with pollinators in mind will broadly benefit wildlife and ecosystem health. Roadsides are also an opportunity to showcase natural beauty and promote tourism, reduce maintenance and thereby provide cost savings to DOTs, and to support a wide range of important ecosystem services including carbon sequestration. Roadsides are an integral part of the highway system and may be valued as important natural resources by the general public, roadside managers, and DOT administrators.

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Chapter 7 - Resources for Roadside Management for Pollinators

Below are some resources for implementing pollinator-friendly roadside management practices. These and other resources may also be available through the Federal Highway Administration’s pollinator resource page, found here: https://www.environment.fhwa.dot.gov/env_topics/ecosystems/pollinators.aspx

Vegetation Management

Guidelines for Vegetation Management
From the American Association of State Highway and Transportation Officials and based on the experience of roadside managers, this manual includes information about weed control, erosion control, native plant establishment, prescribed burning, and other vegetation management techniques.

Vegetation Management: An Ecoregional Approach
This handbook for managers, edited by Bonnie Harper-Lore, Maggie Johnson, and William Ostrum, is one of FHWA’s resources for considering ecoregional contexts in roadside vegetation management.
https://www.environment.fhwa.dot.gov/env_topics/ecosystems_vegetation.aspx

Roadside Weed Management
Invasive species prevention and control, as well as State-by-State weed lists, and a primer on restoration are included in this book. A portion of the book is available as a pdf from:
https://www.montana.edu/extension/invasiveplants/archives_CISM/index.html

Introduced, Invasive, and Noxious Plants
Federal and State noxious weed lists, invasive plant lists, and introduced plant lists, with links to more information.
https://plants.usda.gov/home

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Native Plants and Restoration

Roadside Use of Native Plants
A reference that includes lists of native trees, shrubs, vines, grasses, and forbs for each State.
https://www.environment.fhwa.dot.gov/env_topics/ecosystems/roadside_use/vegmgmt_rdsduse.aspx

Roadside Revegetation: An Integrated Approach to Establishing Native Plants
This manual provides information on native plant establishment from project planning though monitoring after installation. There is also an interactive, multimedia website.
http://www.nativerevegetation.org/

A Manager’s Guide to Roadside Revegetation Using Native Plants
This guide is a resource for engineers and managers to implement native revegetation projects.
https://www.fs.fed.us/wildlifecrossings/library/documents/MangersGuidetoRoadsideRevegetationUsingNativePlants.pdf

Restoration, Nurseries, and Genetic Resources
This website, from technical specialists with the U.S. Department of Agriculture, Forest Service, has resources about growing native plants, including a national seed and nursery directory, and many publications about propagation and plant establishment.
https://rngr.net/

Lady Bird Johnson Wildflower Center
The Center’s Native Plants Database is searchable by plants by State, height, soil moisture, and other characteristics, including value to pollinators.
https://www.wildflower.org/plants/

North American Plant Atlas
From the Biota of North America Program, this searchable plant database also includes county-level species distribution maps.
http://bonap.net/napa

PlantNative
This website includes directories of native plant nurseries and professionals, as well as regional lists of species that are commercially available.
http://www.plantnative.org

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Pollinators and Roadsides

Literature Review: Pollinator Habitat Enhancement and Best Management Practices in Highway Rights-of-Way.
This literature review was developed to inform this Best Management Practices document, and provides a detailed account of the research relating to use of roadsides by pollinators and vegetation management practices.
https://www.environment.fhwa.dot.gov/Env_topics/ecosystems/pollinator_reports/pollinators_BMPs_in_highway_ROW.aspx

What’s the Buzz about Pollinators and Roadsides?
Produced by Minnesota’s Department of Natural Resources, this poster focuses on pollinators and the role roadsides can play in their conservation.
http://files.dnr.state.mn.us/assistance/nrplanning/community/roadsidesforwildlife/beesforroadsides.pdf

Pollinators and Roadsides: Guidelines for Managing Roadsides for Bees and Butterflies
This publication provides an overview of the conservation potential of roadsides and steps to take to maximize the value of these areas to pollinators.
http://www.xerces.org/publications/guidelines/pollinators-and-roadsides

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Pollinator Plant Resources

Regional Pollinator Plant Lists
A resource for finding native plants that are highly attractive to pollinators such as native bees, honey bees, butterflies, moths, and hummingbirds, and are well-suited for small-scale plantings in gardens, on business and school campuses, in urban greenspaces, and in farm field borders.
https://xerces.org/pollinator-conservation/pollinator-friendly-plant-lists

Pollinator Habitat Installation Guides
These regional guides describe how to install and maintain foraging and nesting habitat for pollinators and include region-specific plant recommendations.
https://www.xerces.org/pollinator-conservation/habitat-installation-guides

Attracting Native Pollinators
A guide to pollinators, including profiles of commonly encountered bee genera and more than 50 pages of fully-illustrated plant lists.
https://xerces.org/publications/books/attracting-native-pollinators

Lady Bird Johnson Wildflower Center
The Special Collections section of the Native Plants Database includes lists of plants that are attractive to native bees, honey bees, and other beneficial insects. The lists can also be narrowed down by criteria such as State, soil moisture, and other characteristics.
https://www.wildflower.org/collections/

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Pollinator Biology and Conservation

Pollinator Conservation Resource Center
The Resource Center includes regional information on plants for pollinator habitat enhancement, habitat conservation guides, nest management instructions, bee identification and monitoring resources, and directories of native pollinator plant nurseries.
https://xerces.org/pollinator-resource-center/

Attracting Native Pollinators
A guide to pollinators, including profiles of commonly encountered bee genera and more than 50 pages of fully-illustrated plant lists.
https://xerces.org/announcing-the-publication-of-attracting-native-pollinators/

Bee Monitoring Tools
Designed for conservationists, farmers, land managers, and restorationists, these guides provide instructions for assessing pollinator habitat quality and diversity by monitoring native bees.
https://xerces.org/xerces-bee-monitoring-tools/

How to Reduce Bee Poisoning from Pesticides
From Pacific Northwest Extension, this publication includes common agricultural pesticides and their known effects on bees.
http://www.science.oregonstate.edu/bpp/insect_clinic/pests/pnw591.pdf

Inside Agroforestry – Windbreaks
From the National Agroforestry Center, this publication describes how to design windbreaks with pollinators in mind.
https://www.fs.usda.gov/nac/practices/windbreaks.php

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Chapter 8 - Contributors

Prepared by: The Xerces Society for Invertebrate Conservation in collaboration with ICF International.
Authors: Jennifer Hopwood¹, Scott Hoffman Black¹, and Scott Fleury²
Editor/Contributor: Deirdre Remley³

¹ Xerces Society for Invertebrate Conservation
² ICF International
³ Federal Highway Administration

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Chapter 9 - References Cited

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