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

CHAPTER 1 – Introduction

Table of Contents

• Chapter 1: Introduction
  • Introduction
  • 1.1 An Integrated Approach
  • 1.2 The Ecological Context of Roads
    • 1.2.2 Present Awareness
    • 1.2.3 Trends in Road Construction
    • 1.2.4 Challenges and Opportunities
    • 1.2.5 Why Revegetate Roadsides with Native Plants?
  • 1.3 Objectives of this Report
  • 1.4 Scope
  • 1.5 Approach
    • 1.5.1 Sustainable Revegetation on Roadsides
    • 1.5.2 What is the "Roadside"?
    • 1.5.3 What are Native Plants?
    • 1.5.4 Why the Emphasis on Pollinators?
    • 1.5.5 Goal-Oriented, Context-Sensitive, and Integrated
  • 1.6 How to Navigate through this Report
• Chapter 2: Initiation
• Chapter 3: Planning
• Chapter 4: Revegation Plan Example
• Chapter 5: Implementation
• Chapter 6: Monitoring
• Chapter 7: Operations & Maintenance
• Chapter 8: Case Studies
• References

INTRODUCTION

The Roadside Revegetation report was written to provide current best practices for planning, designing, and implementing a revegetation project and also includes considerations for creating habitat for pollinators. The report identifies steps and considerations in developing a revegetation project from a variety of perspectives, and presents them in a typical design project order from planning through implementation and maintenance. A diverse writing team of experienced civil engineers, transportation engineers, landscape architects, botanists, geneticists, pollinator conservation specialists, soil science specialists, restoration specialists and environmental protection specialists applied their specific experience and knowledge to this report. Technical aspects of the writing were reviewed by Department of Transportation (DOT) civil engineers and landscape architects and revegetation specialists from several state and federal agencies, who also applied their regional perspective on the planning, design, installation, and maintenance processes.

Users of this report may find it beneficial to review Table 1-1 and the Primer for a quick overview of a revegetation process and an outline of the report chapter contents in order to gain an understanding of the full scope of the report and how it is organized. The Primer also provides an introduction to the online Ecoregional Revegetation Application (ERA) tool and the Native Revegetation Resource Library. The ERA is an extensive ecoregional plant database that also includes pollinator value information for each plant. The ERA provides a list of all native plants within an ecoregion as well as a list of “workhorse” plant species, the primary beneficial native plants for pollinators and roadside revegetation in a specific ecoregion, and then allows designers to download either form of information in a digital spreadsheet for evaluation and manipulation for their project(s). The Native Revegetation Resource Library is an online depository that contains copies of applicable revegetation and pollinator educational resource material, referenced from other online sources, compiled in this one location for designer convenience.

This report was written by technical experts for the technical experts involved in the revegetation planning, design, and implementation process. Many report topics include regional and optional considerations and techniques that designers can evaluate for applicability to their project conditions. The writers of this report envision the following ways to use this report:

• Primary Revegetation Reference—Designers, revegetation specialists, and contractors can reference the document as they work through revegetation project planning, design, implementation, and monitoring and maintenance.
• Education Tool—The report may be used in the classroom and field demonstration setting to educate the next generation of designers, installers, and maintenance professionals.
• Supplemental Information—Using the information to revise and supplement existing agency best practices.
• Planning Resource—The Table of Contents (TOC) can be used to identify applicable revegetation tasks for specific projects.
• Scope of Work Development—For creating a revegetation project scope of work for a Request for Qualifications or a Request for Proposal.
• Scope, Schedule, and Budget Resource—The TOC can be used as a template for creating a list of revegetation tasks for an estimate of labor hours, project budget, and project schedule.
• Project Team Evaluation—For evaluating the project team strengths and identifying additional sub-consultant expertise that may be needed for the revegetation project.
• Revegetation Project Agenda Outline—Using the TOC as a project kick-off meeting agenda to discuss revegetation topics and to start team coordination.
• Operations and Maintenance Report—Portions of the information can be used as an outline of the revegetation project operations and maintenance tasks.
• Project Management Resource—The client, managers, and team members can identify the revegetation project tasks and then track progress of each task throughout the project duration.

1.1 AN INTEGRATED APPROACH

Integrating societal goals for safe, efficient transportation with goals for ecological health is a crucial issue that is receiving increased attention from transportation agencies (Forman et al 2003; National Research Council 2005). Today, most road projects involve modifications to existing roads rather than new construction (National Research Council 2005). As roads are modified or updated section by section, a tremendous opportunity presents itself to remedy the oversights of the past, mitigate environmental impacts, and improve conditions for healthy ecosystems (Figure 1-1).

Native plants are a foundation of ecological function, affecting soil conservation, wildlife and pollinator habitat, plant communities, invasive species, and water quality. Although all of these ecological functions are important, recent emphasis has been placed on supporting pollinators and this facet is highlighted throughout this updated report. Establishing locally adapted, self-sustaining plant communities can also support transportation goals for safety and efficiency. Protecting existing native vegetation during construction and establishing native plants on roadsides following disturbance is key to integrating road systems into natural systems.

Past obstacles to establishing native plant communities on roadsides have been technical, informational, and organizational. Designer and project technical success can be achieved when effective strategies and practical techniques for revegetating the disturbed conditions with limited resources are made available to designers. Project success and efficiency can increase when multiple disciplines, ranging from landscape architecture to engineering, soil science, ecology, botany, genetics, entomology, and wildlife conservation are able to communicate and coordinate as a team early in the project planning, working cooperatively, not in isolation. Finally, improved interagency cooperation and planning processes that consider ecological effects at every step can enhance the success of a revegetation project.

This report offers an integrated approach to facilitate the successful establishment of native plants and pollinator habitat along roadsides and other areas of disturbance associated with road modifications. It guides readers through a comprehensive process of initiating, planning, implementing, maintaining and monitoring a roadside revegetation project with native plants and pollinator habitat.

Back to top

1.2 THE ECOLOGICAL CONTEXT OF ROADS

Our road system infrastructure is large, covering millions of acres, with roads under the jurisdiction of Federal land management agencies alone comprising over 17 million acres (Ament, Begley, Powel, Stoy 2014). The road system is widespread and affects all but our most protected lands (National research Council 2005). The total road corridor (paved road plus roadside or right-of-way) covers over one percent of the nation’s land surface, an area equal to the size of South Carolina (Forman and Alexander 1998). If unpaved roads are also included, the percentages increase (FHWA 2008). The ecological effects of roads extend into a zone far beyond the edge of the pavement, with effects including habitat fragmentation, wildlife mortality, noise and chemical pollution, disruption of hydrologic cycles and water quality, increased erosion, and the potential creation of transportation corridors for noxious and invasive weeds that can invade adjacent lands. With these considerations, an estimated 15 to 20 percent of the United States is ecologically affected by roads (Forman and Alexander 1998). The enormous challenge of understanding and mitigating the ecological effects of roads deserves attention and dedication on local, regional, and national scales.

1.2.1 PAST OVERSIGHTS

Much of the existing road network in the United States was designed and constructed prior to the 1970s, in an era before ecological health became a widespread concern among American citizens and before ecological science had evolved to address large-scale issues (Forman et al 2003). Safety and efficiency were the primary goals of transportation programs in the past, and the ecological context of roadways were largely overlooked in planning, construction, and maintenance efforts. The effects of roads on natural systems (habitat fragmentation; interruption of natural flows of water; and disturbances to animals, plants and their pollinators, soils, and other resources) were not well understood or considered. Lack of awareness about these factors led to a largely antagonistic perception of the relationships between natural systems and road systems.

For example, without effective revegetation of the road disturbance with desirable plants, undesirable vegetation can encroach on the roadway. Undesirable vegetation can disrupt safety and visibility, leading to expensive and potentially hazardous maintenance measures. Undesirable vegetation can invade and wipe out areas of desirable native plants that pollinators need for food and cover to survive. Conflicts with neighboring land uses could result if corridors for invasive weeds are established or if vegetation control measures are viewed as a health or safety concern by the community. These are all issues that arise when ecology and revegetation science are not considered during road design, construction, or modification. Eventually, poorly integrated or addressed natural processes can threaten the function and structural integrity of the road itself, leading to premature deterioration of the road’s infrastructure (Berger 2005).

1.2.2 PRESENT AWARENESS 

For over 20 years, the ecological effects of roads have been increasingly recognized by the FHWA and by state and county transportation agencies (National Research Council 2005). Today, road effects on ecological processes are major concerns among private citizens, land management agencies, and the transportation community. Consequently, an emphasis has been placed on the integration of ecological considerations into all phases of road design and construction processes. For example, fish passages have been built to reconnect natural water flows under roads. Other projects have modified roads that were deemed particularly dangerous to endangered species. These roads are being made more permeable to wildlife, greatly reducing losses by improving habitat connectivity, ensuring better visibility for drivers and animals, and creating safer underpasses or overpasses for wildlife (Forman et al 2003). Given the recent decline of pollinator species, there is now a greater emphasis on supporting pollinators by creating habitat on roadsides. A National Pollinator strategy (79 FR 35901) has recently been released, tasking federal agencies to do more with their land holdings, development practices, and maintenance operations to support pollinators in order to reverse pollinator declines (Section 1.5.4). Efforts to limit inappropriate road expansion and to obliterate unnecessary roads remain important. Where modification and increased capacity are needed, ecological health, safety, and efficient transport are not mutually exclusive goals.

Understanding roadside environments, how they interface with adjoining lands, and how to minimize environmental impacts has become a key focus of the Federal Highway Administration. Given political will and proper levels of attention, integration of environmental concerns with transportation can result in significant gains.

1.2.3 TRENDS IN ROAD CONSTRUCTION

For the purposes of this report, the primary focus is on Federal, State, and County road corridors, that include highways, interchanges, rural routes, farm to market routes, river roads, and most roads through our National, State, and County parks and preserves. Roads are widespread, fairly permanent fixtures on the landscape and in the culture of the United States. Given current trends, road networks are expected to persist and expand over time. Current modifications predominantly involve updating infrastructure to increase capacity and to improve safety, including widening roads, replacing bridges, and reducing or altering curves and grades to make the road safer for motorists (National Research Council 2005). The opportunity to integrate ecological goals with transportation was largely overlooked when the road networks were originally constructed. However, as the nation’s roads are being updated and modified, the opportunity cannot be ignored. While attempts to integrate ecological factors are positive, much of the potential for improved integration is still largely unrealized. This has been due, in part, to a shortage of practical information and the absence of an integrated approach to the challenge. The question is, what can be done to balance societal desires for safe, efficient transport with a healthy environment? In other words, what can be done to help road systems function better with natural systems?

1.2.4 CHALLENGES AND OPPORTUNITIES

The fact that the nation’s road networks are in varying states of updates, repairs, and maintenance presents an opportunity to improve road systems so that they integrate better with natural systems. Planners and designers strive to understand detrimental effects associated with roads and how to mitigate them by minimizing the ecological footprint of roads and maximizing potential ecological benefits. Many groundbreaking resources have emerged to support these efforts. Road Ecology: Science and Solutions (Forman et al 2003) places the challenges into comprehensive frameworks, illuminating goals and principles for an ecological approach to transportation issues. Multiple intervention points are identified to help road systems function better with natural systems, integrating transportation goals for safety and efficiency with approaches to protect water, soil, vegetation, wildlife, and aquatic life. The FHWA published a landmark book called Roadside Use of Native Plants (Harper-Lore and Wilson 2000) that brought the issue of native plant communities on roadsides to the forefront in the transportation community, highlighting the importance of native plants and their broad utility. The National Research Council of the National Academies of Science expanded on the frameworks identified in Forman et al (2003) in its publication, Assessing and Managing the Ecological Impacts of Paved Roads (2005). Processes within the FHWA, state DOT, and other agencies are being improved for better integration.

In addition to these advances directly related to roads, many advances in the field of restoration ecology have distilled essential principles applicable to severely degraded sites (e.g., Munshower 1994; SER 2004; Clewell et al 2005; Claassen 2006). In addition, vegetation specialists from a variety of organizations have come to consensus about what truly defines a “native” plant and have developed seed collection, transfer, and propagation principles to ensure that locally adapted materials are used for optimum results (Withrow-Robinson and Johnson 2006, Johnson et al 2010, Basey et al 2015). In both the public and private sectors, seed and plant producers and installers have been developing innovative methods to meet unique site conditions.

Recently, the opportunity to support declining pollinator species through habitat creation on roadsides has been addressed with great success (Hopwood et al 2015, Hopwood et al 2016a, and case studies in this report). Designers have created “pollinator-friendly” roadside habitat, and agency maintenance departments have altered procedures to better maintain these habitats with a focus on the needs of pollinators.

While the publications above assess the best available conceptual and practical information, each also recognizes extensive needs for further work. Central to ecosystem function is native vegetation (SER 2004). However, much of the pertinent information related to protecting and establishing native plants on roadsides has been difficult to put into practice. This report is intended to bridge some of the informational, technical, and organizational gaps to facilitate successful roadside revegetation with native plants. An integrated approach is offered to support both designers and field-based practitioners in successfully revegetating roadsides and obliterated roads with native plant communities (Figure 1-2).

1.2.5 WHY REVEGETATE ROADSIDES WITH NATIVE PLANTS?          

Long-term economic and ecological advantages can be gained by establishing desirable native plant communities on roadsides (Berger 2005). Roadside vegetation can support safety goals by reducing headlight glare, reinforcing the road alignment, protecting view planes and visibility, controlling snow drifts, and reducing wind speeds (Forman et al 2003). Pollinator-friendly plants species, many of which are showy flowering plants, can improve the experience of the road user by creating natural beauty via plant form and color diversity along the roadside, in addition to improving driver performance by reducing monotony and stress. Importantly, creating pollinator habitat along roadsides can directly support imperiled pollinators such as the iconic monarch butterfly (Danaus plexippus), economically important managed species such as the European honey bee (Apis mellifera), as well as a wide variety of native pollinators including wild bees, butterflies, moths, flies, beetles, and wasps. A self-sustaining native plant community on a roadside stabilizes slopes, protecting water and soil quality. In addition, the establishment of healthy native plant communities is often the best long-term defense against invasive and noxious weeds. Maintenance costs for managing problematic vegetation are reduced, as is the pollution and controversy that sometimes results from roadside herbicide use (Berger 2005). Establishing healthy roadside vegetation can also help sequester carbon dioxide, one of the factors responsible for global climate change (Palumbo et al 2004, Ament et al 2013).

Using native vegetation supports every aspect of the goals identified as best management practices by the transportation community for road design. These include goals to:

• Produce a safe, cost effective, environmentally friendly, and practical road design that is supported by and meets the needs of the users
• Protect water quality and reduce sediment loading into water bodies
• Protect sensitive areas and reduce ecosystem impacts
• Maintain natural channels, natural stream flow, and passage for aquatic organisms
• Minimize ground and drainage channel disturbance
• Control surface water runoff and stabilize the roadbed driving surface
• Control erosion and protect soil
• Implement slope stabilization measures and reduce mass wasting
• Stormproof and extend the useful life of the road (Keller and Sherar 2003)
• Create and maintain pollinator-friendly habitats (Hopwood et al 2015)

Clearly, the goals of safe and efficient transportation and the goals of establishing and protecting native vegetation overlap; when properly integrated, native vegetation supports road objectives. At the same time, considering vegetation as part of road planning processes aids in minimizing and mitigating the ecological footprint of roads during and after construction. Native plants can provide wildlife habitat and improved connectivity for the length of the road (Forman et al 2003). Understanding vegetation and forage preferences, and careful design that accounts for visibility and safety, can guide animals to safe passageways for travel while minimizing dangerous interactions with vehicles. The presence of birds and small animals can be enhanced when appropriate plant species are established. Processes that work for roadside revegetation are also applicable to the process of obliterating roads where roads are no longer needed.

Despite the potential benefits, many past attempts at roadside revegetation have not succeeded. Although revegetation was considered important, some efforts emphasized seeding of exotic plants; these species were perceived as inexpensive, readily available, and easy to establish on disturbed sites, however, this practice has not been effective or self-sustaining on many projects; either the exotic plants spread to become problematic, or failed to persist because they were not locally appropriate species. Once established, exotics may preclude reintroduction of desirable natives. In other cases, little consideration was given to establishing roadside vegetation during or after construction; if vegetation was considered, it was often as an afterthought. A short-term approach to revegetating roadside disturbances often predominated past efforts, while efforts toward long-term development of native plant communities did not receive adequate consideration. The ineffectiveness of revegetation efforts in the past has resulted in such problems as soil erosion and landslides that affected water quality (Figure 1-3). Visually, unvegetated road disturbances diminish the experience of the road user and economically translate into high costs associated with ongoing maintenance.

Past shortcomings may be attributed to past approaches that were often piecemeal and lacking the cooperation and coordination of disciplines necessary to fully integrate native vegetation into the road planning and construction processes. Revegetation specialists typically worked in isolation from engineers, and sometimes even the biological specialists (soil scientists, botanists, wildlife biologists) failed to coordinate their knowledge and efforts. Success depends on both practical and technical information and a systematic, comprehensive approach.

Back to top

1.3 OBJECTIVES OF THIS REPORT

For the Designer
This report is not prescriptive but instead provides principles and a step-by-step process of revegetation.

This report brings theoretical and practical information to bear on the challenge of revegetating roadsides with native plants. Written by and for project designers and field-based practitioners, it synthesizes a comprehensive, holistic approach that can be used to effectively revegetate roadsides and other similarly disturbed areas. Given the unique ecological factors at play on each project, the report is not prescriptive, but rather provides principles and a step-by-step process for designers to use in the field to generate and implement their own locally appropriate, context-sensitive revegetation plan. Examples and proven strategies are offered to serve these goals. Topics covered include how to:

• Improve interagency cooperation in order to think ecologically about road modifications and make revegetation an integral part of road design
• Coordinate information and efforts to bring multiple disciplines such as soil science, genetics, botany, ecology, wildlife science, landscape architecture and engineering together for a holistic approach to revegetation
• Integrate goals for native vegetation establishment with transportation goals for safety, function, and efficiency
• Mitigate harsh, drastically disturbed conditions of road disturbance areas to enable native plants to establish through natural colonization and/or active replanting
• Apply a step-by-step planning, implementation, and monitoring process, including mid-course corrections, to overcome potential pitfalls, resulting in cost-effective, successful establishment of native plants
• Share knowledge, including new revegetation tools and techniques

Back to top

1.4 SCOPE

The complexity of ecologically sensitive road design, implementation, and maintenance can benefit from increasing cooperation from multiple sectors of society and multiple fields of practice and expertise. This report may be of interest not only to field-level practitioners and project designers in both public and private sectors, but also to transportation and planning professionals; land managers; policy-makers; owners and operators of roads on county, state, and federal scales; and concerned citizens. Any agency or organization involved in altering, developing, operating, maintaining, or decommissioning roads will find this publication useful. This report is especially intended to serve field-based practitioners and planners of diverse backgrounds whose goal is to establish locally appropriate, low-maintenance native plant communities on roadsides.

Because integration of multiple sources of expertise is necessary for effective long-term revegetation, this report does not assume that the designer has a particular specialized background but more, a broad level understanding of such disciplines as botany, plant propagation, soil science, genetics, entomology, landscape architecture, and engineering. The designer may be one of these specialists and may involve one or more of these other specialists during the planning process, depending on the project’s complexity. The report states where specific expertise may be appropriate. Key information specifically for designers or contractors and key milestones for communication and integration between engineers and non-engineers are highlighted.

The approach in this report is applicable to any type of road-related project that involves disturbances to soil and vegetation. Revegetation of roadsides adjacent to dirt, gravel, and paved roads would involve similar processes, although there are differences in scale and intensity of efforts. This report applies to new construction or reconstruction and modifications of existing roadways. The principles and practices are also applicable in revegetating other drastically disturbed sites with similar limiting factors to roadsides, such as utility, gas, oil, or powerline rights-of-way and mine reclamation projects.

This report focuses on opportunities for integration during road construction or modification. Long-term maintenance and management of established roadsides is discussed briefly, with references to related management practices such as Integrated Roadside Vegetation Management (IRVM) (Berger 2005). Roadsides that are more permeable to natural flows of water help mitigate the ecological effects of the road. Efforts to improve habitat connectivity and road permeability, as well as storm-water drainage and created wetlands, can be supported by the revegetation practices described in this report. However, specific mitigations for these important topics are beyond the scope of this publication. Also beyond the scope are the myriad other potential ecological and social issues that affect, and are affected by, the engineering and transportation planning processes. Issues of community planning are not addressed. Larger policy-making and planning procedures are also beyond the scope of this report.

Back to top

1.5 APPROACH

The establishment of native plant communities, in order to reinitiate natural processes of succession is a cornerstone of most ecological restoration work (Dorner 2002) (Figure 1-4). Effective revegetation on highly disturbed roadsides aims to initiate or accelerate processes of natural succession following disturbances. Three aspects are generally considered: (1) health (the functional processes of the ecosystem); (2) integrity (species composition and community structure); and (3) sustainability (resistance to disturbance and resilience) (Clewell et al 2005). While restoring plant communities to a pre-disturbance state is not typically a goal on highly disturbed roadsides, each of the above three ecosystem aspects can be improved with appropriate roadside revegetation practices. The establishment of reference sites, or natural models for the desired recovery process, is key to identifying and overcoming limiting factors and accelerating succession by establishing native plants.

Native species play an important role in ecosystem development. If native species can become established on a disturbed site, the processes of succession, including soil recovery and nutrient cycling, are initiated (Brown and Amacher 1999). In most cases, native plants are established on roadsides through seeding or planting, although sometimes passive revegetation (natural colonization) is possible where native seed banks are nearby and limiting factors are mitigated.

1.5.1 SUSTAINABLE REVEGETATION ON ROADSIDES

Sustainable revegetation projects attempt to integrate disturbed sites with the surrounding, non-disturbed landscape. An ideal integration is both visual and functional in nature, and the blending of the two is often considered an art.

Revegetation efforts are most likely to be sustainable if they are process based in approach, rather than form based. Process-based projects aim to create healthy and resilient ecosystems with the necessary components to develop multiple natural processes. Many desired natural processes take hundreds of years to fully develop, so it is unreasonable to think a designer can anticipate, replicate, and accelerate their development over the course of a project that might span three, five, or ten years. The objective, rather, is to install as many components of as many processes as possible, to facilitate their development. In this sense the designer is often most interested in the trajectory of the developing processes, rather than their presence in complete form.

The purpose of this section is not to discuss every possible contributor to resiliency or process building. Rather, it is to provide the designer with information that might assist in the recognition of actions they can take to potentially increase resiliency and accelerate the development of natural processes.

Supporting Resiliency

Resiliency is a system’s ability to recover quickly, and hopefully entirely, from disturbance. The use of genetically appropriate plants, collected from throughout the project and surrounding area within the provisional seed zone(s), can encourage genetic health and resilience of the restoration plant population as well as those populations surrounding the project area. Restoration plants, installed at sufficient spacing, can increase competition and facilitate the site’s resistance to invasion by non-native or weedy plant species, thereby making it more resilient to plant compositional changes when they do occur. Plant species and form diversity creates redundancies in life form, functional grouping, and services; all of which increase resiliency.

Consideration of Natural Processes

Multiple natural processes have components for which the designer can assist when re-integrating a disturbed site into the surrounding landscape. The designer may want to identify and initiate the enhancement or construction of those processes that already naturally occur, or would be expected to occur, on the surrounding landscape. There would be little point in allocating resources to try to develop a wetland in a sage steppe of a high desert upon which no wetlands occur, for example.

Soil forming processes can be considered during a number of project activities such as decommissioning roads, constructing cut and fill slopes, or when shaping the final grade of spoils areas. Knowing that wind and water erosional forces shape and sculpt land formations, attention to the contours of the surrounding landscape can inform designers and equipment operators of how best to blend the target area with its environment. By doing so the newly formed contours not only visually re-integrate the project site into the surrounding setting, but also prevents out-of-proportion, angular, or inappropriate landforms from interrupting wind and water patterns. In addition, the accumulation of plant detritus is a basic component of soil formation. It is often useful to de-compact the soil and leave the site in a roughened, irregular, and undulating condition. The resulting hummocks and low spots can seem small and inconsequential, but they provide pockets for soil to accumulate and will eventually support plant life. Avoiding compaction of the soils frequently provides for better water infiltration and drainage, reduced erosion, and overall stability of soil particles.

The use of annual and perennial plants in revegetation projects contributes plant litter to the system throughout a prolonged period of time compared to a site that only uses one or the other. This litter then becomes reduced and incorporated into disturbed sites, facilitating the nutrient cycling. Including various plant life forms in a revegetation plan, including shrubs and trees where appropriate, provides refuge, breeding-, feeding-, rearing-grounds, as well as domicile habitat for insects, birds, and various small and large animals. The abundance and diversity of organisms supported on the revegetation site contribute greatly to the development of a functioning nutrient cycle. In addition to facilitating nutrient cycling, the abundance and diversity of organisms supported also play critical roles in the dispersal of seeds and spores.

Considering Maintenance Operations and Costs

Sustainability from the maintenance stand point is a component that is easy to overlook, when focused on the biology of a project. Roadside maintenance programs are designed to insure the safety of travelers and to protect the integrity of the road. If the life forms planted are inappropriate for the roadside, if setbacks or roadside zones are ignored, if the structural integrity of the selected plants is not sound, or if the restoration plantings create visibility and safety issues, then the revegetation project will not be sustainable. Maintenance operations and costs are components to be considered in all phases of a revegetation project as its success and sustainability is partially dependent on understanding the needs of roadside maintenance programs.

1.5.2 WHAT IS THE “ROADSIDE“?

In this report, the term “roadside” refers to any area of disturbance associated with road construction, reconstruction, waste areas, source pits, and maintenance, (Figure 1-5). The roadside includes the sides of the road corridor beyond the paved road (shoulders and verges), including impacted or maintained roadside areas within the right-of-way. The roadside area is sometimes narrow, but sometimes extends several hundred feet or more beyond the edge of the road surface, depending on the project. In some situations, revegetation efforts may encompass areas beyond the right-of-way that are affected by or affect the road. The area where the revegetation specialists will focus their efforts is usually dependent on two factors: ownership of the right-of-way and surrounding lands, and areas of disturbance (construction footprint). Most roadsides are drastically disturbed environments, where soil may be severely compacted and consist of a mixture of subsoil and parent material (Figure 1-6). Beneficial microorganisms, nutrients, and organic matter necessary to sustain plant growth may be absent or severely depleted. Often, slopes can be very steep and inaccessible, exposed to the erosive effects of wind and water. These environments represent a revegetation challenge of high intensity and magnitude.

1.5.3 WHAT ARE NATIVE PLANTS?     

“Native plants,” as defined in this report, are locally adapted, genetically appropriate native plant materials (Withrow-Robinson and Johnson 2006). These plants are best suited evolutionarily to the local conditions, and generally need less maintenance and persist longer than non-local species. When properly established, they form plant communities with the potential to be self-sustaining and self-perpetuating over time, requiring little or no input from humans to persist. Native plants also support more robust communities of pollinators, birds, and other small wildlife.

Challenges to establishing native plants on roadsides are significant, partially due to difficulties in obtaining appropriate materials. However, the technological capacity of native plant propagation and outplanting efforts in both private and public sectors has increased significantly in the past two decades. Innovative stocktypes and application methods have made roadside revegetation more effective. Federal agencies that manage roads increasingly use native plant materials as the first choice in revegetation efforts, thereby making roadside revegetation an important and expanding frontier for native plant suppliers.

1.5.4 WHY THE EMPHASIS ON POLLINATORS?

An estimated 85 percent of the world’s flowering plants depend on animals for pollination (Ollerton et al 2011). Animal pollinators visit flowering plants seeking floral resources and, in the process, incidentally transfer pollen from anthers (male reproductive structures of the flower) to stigmas (female reproductive structures), vectoring fertilization and allowing these flowering plants to reproduce. Pollinators rely on flowering plants for food, requiring nectar (a sugar-rich liquid) and sometimes pollen itself (a source of protein) as sources of energy and nutrition. Most animal pollinators are insects, such as honey bees, bumble bees, flies, and butterflies. However, vertebrates such as birds (e.g., hummingbirds), mammals (e.g., bats, rodents) and some reptiles pollinate certain plant species. The pollination services provided by pollinators are essential to the health and persistence of the plant species that depend on them, and for the wildlife and pollinators that in turn depends upon the plants for food, nesting, and shelter.

Pollinators are also important to human health and the global economy. More than 75 percent of the world’s 115 principal cultivated crops are reliant on animal pollinators or benefit from animal pollination. Roughly 35 percent of global crop production is dependent on pollination by animals (Klein et al 2007). Insect-pollinated forage plants such as alfalfa and clover also provide feed for livestock. Pollinator-dependent food crops, namely fruits, vegetables, and nuts, make up a critical component of our diet (McGregor 1976). The majority of minerals, vitamins, and nutrients needed to maintain human health (such as vitamin C, lycopene, calcium, and folic acid) come from crop plants that depend partially or fully on z pollinators (Eilers et al 2011). Consequently, pollinators provide essential agricultural services with a high economic value. A recent worldwide estimate suggests pollinators in general contribute 9.5 percent ($216 billion per year) to crop value (Gallai et al 2009). In the United States, it is estimated that pollinators (both managed and wild) contribute $29 million in farm income annually (Calderone 2012). Importantly, native pollinators specifically have been shown to contribute approximately $1 billion to the California crop economy (Chaplin-Kramer et al 2011).

Globally, pollinators are in decline (National Research Council 2007; Potts et al. 2010). In the United States, wild pollinators such as monarch butterflies and many bumble bee species, as well as colonies of managed honey bees, are experiencing declines due to a loss of habitat, the spread of disease, overuse of pesticides, and various other factors (National Research Council 2007; Hatfield et al 2015; Jepsen et al 2015). Pollinator declines threaten the viability of agricultural productivity and the health of natural ecosystems.

With at least 17 million acres of roadsides in the United States, roadside vegetation can serve as much needed habitat for pollinators, offering food, breeding, or nesting opportunities and connectivity that can aid pollinator dispersal (Hopwood et al 2015). Roadsides can support a diversity of generalist pollinators, including bumble bees, honey bees, butterflies, and hummingbirds as well as rare or federally listed species. Roadsides sustain plants that are sources of pollen and nectar for adult pollinators as well as host plants for the caterpillars of butterflies and moths. The availability of floral resources influences the abundance and diversity of butterflies and bees found on roadsides (Saarinen et al 2005; Hopwood 2008). Pollinators on roadsides benefit in particular from native plants (Ries et al 2001; Hopwood 2008). Roadsides planted with native plants also can provide pollinators with shelter, sites for nesting or egg-laying, and overwintering habitat. Pollinators have complex life cycles, with different needs at different stages of their lives. Roadsides can provide resources for a portion of the life cycle of some species, while providing resources needed for the entire life cycle of other species.

Evidence also suggests that the linear shape and connectivity of roadsides may help pollinators to move through landscapes in search of food or in pursuit of new habitat (Ries et al 2001; Dirid and Cryan 1991). Roadsides extend through all landscapes and can be particularly important sources of habitat for pollinators in highly altered landscapes such as intensely managed agricultural lands (Figure 1-7).

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 (Smallidge and Leopold 1997; Johst et al 2006; Reis et al 2001). Roadside vegetation management influences how pollinators use roadsides, and even influences the number of pollinators killed by vehicles. For example, butterfly vehicle mortality rates increase with more frequent mowing and decrease with high plant diversity in roadside vegetation (Skorka et al 2013) (Figure 1-8).

Figure 1-8 | Roadside mowing
Although mowing a clear zone directly adjacent to the pavement poses little harm to pollinators, frequent roadside mowing of the entire roadside can decrease the densities of pollinators.
Photo credit: Idaho Transportation Department

Roadsides play an important role in the conservation of declining wild pollinators and in supporting the health of managed pollinators. Throughout the revegetation process, practitioners and designers can enhance roadsides to benefit pollinators.

1.5.5 GOAL-ORIENTED, CONTEXT-SENSITIVE, AND INTEGRATED    

The overall approach in every aspect of this report is goal-oriented, context-sensitive, and integrated (Clark et al 2001). The goals of establishing and protecting native plant communities are considered along with transportation goals, including safety, efficiency, and cost-effectiveness for the life of the road. This is not an idealistic approach; while recognizing that resources are limited and conditions are degraded, the approach is technically and economically feasible while still enabling the integration of roads with ecological processes.

Sensitivity and appropriateness to the local context are essential parts of successful revegetation. This report is intended to facilitate the process of developing locally appropriate, context-sensitive principles on a project-by-project basis, integrating top-down and ground-up information to meet the specific challenges at hand. For this reason, the report does not provide cookbook-type “recipes” or specific prescriptions. For example, no “one- size-fits-all” seed mix exists for roadside revegetation. The process and tools needed to arrive at context-sensitive solutions are not difficult to apply; by following the steps outlined in this report, practitioners will be able to generate the information they need.

Back to top

1.6 HOW TO NAVIGATE THROUGH THIS REPORT

Navigating through this report can be done in several ways:

• Search Field—The easiest way to find a topic in this report is to use the “Search” field. If the topic is very specific, this may be the quickest method. However, if it is a broad topic, discussed throughout the report, this method may not easily narrow down the location in the report. When this is the case, referring to the table of contents and/or using search tools (for digital formats) may be the better approach.
• Table of Contents—The table of content is a quick way of getting to the main sections of the report through hyperlinks.
• Revegetation in 15 Steps—For those who wish to see the revegetation process in a step by step approach may want to use Table 1-1 to navigate through the report. Case studies of completed revegetation projects that create habitat for pollinators are provided in Chapter 8.

Back to top

Table 1-1 | Revegetation in 15 steps

	Revegetation Process Steps		Further defined here
INITIATION PHASE	1	Due diligence, plan development	Chapter 2
PLANNING PHASE	2	Objectives and desired future condition	Section 3.2, Section 3.7
	3	Pre-field information	Section 3.3
	4	Revegetation units and reference sites	Section 3.4, Section 3.5
	5	Field information	Section 3.6
	6	Limiting factors to plant establishment and pollinator habitat	Section 3.8, Section 3.9
	7	Site resources	Section 3.10
	8	Maintenance strategy	Section 3.11
	9	Site improvement treatments	Section 3.12
	10	Plant species	Section 3.13
	11	Plant establishment methods	Section 3.14
	12	Revegetation plan	Section 3.15, Chapter 4
IMPLEMENTATION PHASE	13	Implementation	Chapter 5
MONITORING AND MAINTENANCE PHASE	14	Monitoring	Chapter 6
	15	Operations and maintenance	Chapter 7

Back to top