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From Tech Transfer Newsletter, Summer 2004 » printer-friendly

The Nature of Roadsides

(Summer 2004 Tech Transfer Newsletter)

Roadside vegetation must be managed for safety considerations, aesthetic reasons, environmental mitigation, storm water pollution prevention, and erosion control purposes. Appropriate planting can reduce headlight glare, increase fire retardance, increase windbreak protection, and even reduce graffiti on retaining walls and noise barriers.

Because safety has always been and will always be the number one priority for transportation decision makers, roadside vegetation managers typically favored grasslands. Until recently, readily-available, agricultural, non-native grasses that bred predictably and established easily were commonly chosen. However, native grasses, which can be planted almost as easily, can fill that practical and predictable niche in roadside vegetation. Once established, appropriate native grasses can save maintenance dollars over time, provide a self-reliant and hardy plant community, and protect the local character and natural heritage of a site.

Why Native Plants?

Worker and traveler safety are improved. Established native plants require less maintenance than non-native species, so work crews spend less time on roadsides.
Use of herbicides is reduced. Native plant communities are composites of complementary vegetation types that grow together in natural order and resist weed infestation.
Roadside maintenance costs are lowered. Less frequent, less intensive maintenance and the reduced use of herbicides translates into savings.
Roadside fire hazards may be reduced. Some California native plants, particularly the many low-growing, cool-season native grasses, produce less fire fuel than comparable non-native species.
Water is conserved. California native plants thrive on seasonal rainfall and available ground water. They've evolved to succeed in their natural environment and do not require supplemental irrigation that is both costly and a drain on California's limited water resources.
Effective erosion control. Many native drought-tolerant plants help anchor the soil by growing deep, sturdy roots to tap water resources deep underground.

The Botanical Management Area signs identify environmentally significant roadside reserves where travelers may view California native vegetation as it may have appeared more than a century ago. These signs also alert Caltrans maintenance crews working in and near these sensitive areas. The sign depicts some of the native plants commonly found along California's roadsides: California poppies, lupines and goldfields.

Protecting Remnants

The best way to establish a native plant community is by not undermining or destroying it in the first place; preservation being the easiest and cheapest way to manage a roadside. Ironically, roadsides are sometimes the last refuge of unique plant communities or plant species.

The California Department of Transportation began a plant community preservation effort in 1994, with the goal of improving the success of native wildflower plantings on Caltrans' roadsides. Working with conservation groups, they identified 20 quality native landscape remnants on highway right-of-way. Called Botanical Management Areas, each area is signed and has its own management plan. This effort has since evolved into a holistic approach to highway planting and native landscape restoration.

You may already have native grasses and wildflowers along your roadsides that you don't recognize. If you stopped mowing for one season, you and your state botanists could identify what plants are in the right-of-way and determine whether the vegetation is worth saving. If it is a quality remnant, you could save a piece of natural history, more valuable than any you could plant in its place, and at no cost or effort.

Mowing Less

Reduced mowing saves labor and expense, and improves the roadside environment by increasing small mammal and bird habitat, and aiding the fight against weeds and invasive plants.

To provide a recovery zone for errant vehicles, it is important to mow one to two widths off the pavement edge. However, mowing the entire width of the right-of-way is not necessary and is no longer common practice. Studies show that woody plant invasion of clear zones and back-slopes takes many years before becoming hazardous to travelers. One study suggests that crews might mow the entire right-of-way once every five years to prevent tree growth in forested regions, and mow the area directly adjacent to the roadway more frequently.

For optimal weed control, mowing should be well timed. Spot mowing that targets Canada thistle and other noxious weeds on the roadside are less costly than blanket mowing.

Avoid mowing too short, which scalps the plants and soils and inadvertently causes more weeds to invade.

Avoid flail mowers, unless your intention is to disturb the soil for possible seeding operations.

Herbicides

Herbicides continue to be an important landscape maintenance tool. For some invasive plants, spraying is the only answer. Take advantage of technological and knowledge advances to target weeds by species, using less product, spraying more safely, and minimizing the impact to the environment and the desirable plant species in the area.

References

CaliforniaWILD. California Wildflowers in Landscape Design, California Department of Transportation.
www.dot.ca.gov/hq/LandArch/CaliforniaWILD/index.htm

Highway Design Manual, Chapter 900, Landscape Architecture. California Department of Transportation: 2001.
www.dot.ca.gov/hq/oppd/hdm/pdf/chp0900.pdf

The Nature of Roadsides and the Tools to Work with It (FHWA-EP-03-005). Office of Natural and Human Environment, Federal Highway Administration, US Department of Transportation: 2003.