ROADSIDE REVEGETATION

An Integrated Approach to Establishing Native Plants and Pollinator Habitat

3.2 Defining Revegetation Objectives

The design objectives of a road project guide the development of the revegetation plan. As discussed in Chapter 2, road objectives usually involve goals of improving safety and efficiency, as well as environmental health. Revegetation objectives develop from road objectives and become the foundation of the revegetation and monitoring plans. It is important to develop a clear set of revegetation objectives early in the planning phase. When these objectives are understood and expectations are clear, the development and implementation of a revegetation plan are easier and more successful. Most roadside revegetation projects share the common objective of initiating and/or accelerating the process of natural succession near the roadside in order to establish self-sustaining native plant communities (Brown and Amacher 1999; Clewell and others 2005). This objective usually reflects larger project goals, stated in terms of increasing pollinator habitat, protecting soil and water resources, carbon sequestration, enhancing roadside aesthetics, limiting invasive plants, and improving road safety and function while protecting environmental health. Later in the planning process, revegetation objectives are used to develop specific goals (stated as DFC targets) for evaluating the success of the revegetation work. Table 3-2 defines some terms commonly used in defining revegetation objectives. Clarifying whether the overall goal is reclamation or restoration, for example, is an essential distinction for defining revegetation objectives.

Table 3-2 | Terms used in defining revegetation objectives

Term

Definition

Revegetation

To reestablish vegetation on a disturbed site. This is a general term that may refer to restoration, reclamation, and rehabilitation.

Restoration

This is the re-creation of the structure and function of the plant community identical to that which existed before disturbance. The goal of restoration is conservation, with the intention of maximizing biodiversity and functioning.

Reclamation

This is the re-creation of a site that is designed to be habitable for the same or similar species that existed prior to disturbance. Reclamation differs from restoration in that species diversity is lower and projects do not re-create identical structure and function to that before disturbance. However, a goal of long-term stability with minimum input is implied.

Rehabilitation

This process creates alternative ecosystems that have a different structure and function from the pre-disturbance community, such as a park, pasture, or silvicultural planting.

Adapted from Allen and others 1997

Table 3-3 illustrates some of the most common road-related revegetation objectives as they relate to the road design goals. Most revegetation projects state several objectives to address both short-term and long-term outcomes. For example, short-term, immediate revegetation objectives on most projects include erosion control and water quality protection through mulch and vegetative cover. A long-term revegetation objective would be to establish a native plant community, with a range of plant species that benefit pollinators by increasing foraging, breeding, and nesting habitats. Table 3-4 outlines roadside objectives specific to enhancing pollinator habitat. While short-term objectives might rely on quick-growing ground covers such as grasses and forbs, long-term objectives are often broadened to include such revegetation treatments as planting deep-rooted tree and shrub seedlings to stabilize roadsides, creating visual screens of road infrastructure, and/or supporting sustained native plant community development.

Table 3-3 | Native plants are used to meet road and revegetation objectives

Revegetation objective

Function of native plants

Pollinator habitat enhancement

An important revegetation objective is to improve pollinator habitat by selecting a mix of plant species and site improvements that encourage foraging, breeding, nesting, and overwintering of a variety of pollinator species (Table 3-4).

Erosion control

Controlling surface erosion and thereby protecting soil and water quality is a high priority on road construction projects. Native grasses, forbs, and other herbaceous plants can help meet this challenge, particularly when they are accompanied by appropriate mulching treatments. Deep-rooted native trees and shrubs can also enhance stability of cut and fill slopes.

Water retention

Runoff from road surfaces and cut slopes concentrate water into ditches during rainstorm events, increasing the amount of water that normally enters natural drainage ways. Practices that use native plants in the design, such as constructed wetlands and bioretention swales, amended ditches and fills, filter strips, can help retain much of this water on the project site, reducing the amount of sediments and road pollutants from entering stream courses. The additional water increases the productivity of the established plants.

Weed control

Roadsides can be corridors for the transport and establishment of noxious or invasive weed species. Once established, weeds are hard to eradicate and become seed sources for further encroachment. Revegetating with desirable native species minimizes opportunities for problem species to establish.

Carbon sequestration

Roadside revegetation with native plants can help improve air quality and the health of the public and environment by plants taking in and reducing the amount of carbon dioxide in the atmosphere. Plants store the carbon in the soil long-term and release beneficial oxygen. Native roadside vegetation requires less mowing maintenance, herbicides and pesticides, which reduces carbon in the atmosphere and reduces maintenance costs and associated emissions.

Visual enhancement

Vegetation is often used to enhance the aesthetic experience of the traveler. Wildflowers add color and beauty throughout the growing season; deciduous trees provide shade, vertical structure, and change color in fall; and evergreen species stay green all year, adding visual interest, structure, and green color all year. Vegetation can also be used to frame views, soften views or hide structures such as gabion walls or slopes covered by riprap.

Wildlife enhancement

Many roads intercept animal corridors. Designing native plantings into animal underpasses or overpasses can make roads more permeable to wildlife. The presence of birds and small animals can be enhanced when appropriate plant species are reestablished.

Cost management

Advanced planning, an integrated approach, and the use of appropriate stocktypes and equipment all facilitate successful and cost-effective revegetation.

Table 3-4 | Roadside objectives for enhancing pollinator habitat

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.

Pollinators

Food

Shelter

Revegetation Goals

Bats (nectar feeding species)

Nectar, pollen, fruit

Caves and mines

  • Include food plants

Bees:
Bumble

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

  • Increase density and diversity of native flowering plants
  • Provide native bunch grasses for bumble bee nesting habitat
  • Provide areas with partially vegetated well-drained soil
  • Provide living and dead pithy and woody vegetation

Bees: Ground-nesting

Nectar for adults; nectar and pollen collected as provisions for larvae

Nest in bare or partially vegetated, well-drained soil

Bees:
Tunnel-nesting

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 or prey such as aphids, slugs, insect eggs, as larvae or adults

Larvae overwinter in loose soil or leaf litter; Adults shelter under rocks, logs, brush

  • Increase density and diversity of native flowering plants
  • Provide refuge from burning and grazing during dormant season and early spring

Butterflies/moths: Caterpillar

Leaves of larval host plants

Host plants

  • Increase density and diversity of native flowering plants
  • Include host plants
  • Provide refuge from burning and grazing during dormant season and early spring

Butterflies/moths:
Adult

Nectar; some males obtain nutrients, minerals, and salt from rotting fruit, tree sap, animal dung and urine, carrion, clay deposits, and mud puddles

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

Larvae found on plants near prey; pupae and adults overwinter in soil or leaf litter

  • Increase density and diversity of native flowering plants
  • Provide refuge from burning and grazing during dormant season and early spring

Hummingbirds

Nectar, insects, tree sap, spiders, caterpillars, aphids, insect eggs, and willow catkins

Trees, shrubs, and vines; typically need red, deep-throated flowers, such as twin berry or penstemons

  • Increase density and diversity of native flowering plants, particularly species with deep throats

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

  • Increase density and diversity of native flowering plants
  • Provide areas with partially vegetated well-drained soil
  • Provide living and dead pithy and woody vegetation

Revegetation objectives are often developed by the designer and design team and are supported by, or integrated with, public documents such as Environmental Assessments or Environmental Impact Statements. The objectives sometimes originate from a state or federal agency and motivated by environmental concerns and regulations regarding water quality, erosion control, and vegetation establishment. In the early stages of planning, revegetation objectives are broad and general. As the project evolves, objectives are translated into more precise and measurable goals (DFC targets). After the installation is complete, DFC targets and revegetation objectives will be used to monitor, evaluate, and manage the project.