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Along a few favored stretches of California highway, wildflowers are encouraged to bloom - and sometimes they're even planted by road maintenance workers. These oases along the asphalt desert are beautiful and admired, but few travelers realize that these areas also represent one of the most effective means of controlling roadside weeds: using competitive vegetation - rather than synthetic chemical herbicides - to choke out unwanted plants. Beauty is an added bonus.
If California committed adequate funds to emphasizing native vegetation as competition to weed species, it could be in the forefront of a growing movement toward ecologically responsible roadside management. Such an approach would also greatly reduce costs since native plants live year-round through diverse weather conditions and, if chosen well, can keep visibility open and motorists safe without requiring annual maintenance.
Caltrans once pledged to support competitive vegetation programs but has yet to budget funds to support a serious project. In its 1992 EIR, the agency promised to "shift from chemical control to no control, emphasizing the use of competitive, desirable vegetation." Unfortunately, this goal has not been achieved because very little action has followed Caltrans' rhetoric.
Using native plants as competitive vegetation is now being explored for roadside management in other states where it's recognized as a highly effective technique that crowds out weeds and prevents invasive exotic plants from establishing a foothold. Not only are roads being made safe from the dangers of toxic chemical herbicides, endangered or threatened species are being preserved for future generations.
Promoting the growth of plants indigenous to their surroundings also increases a roadside's fire resistance and prevents erosion. Native plants tend to establish deeper roots and, although they burn when ignited, many are more effective in preventing the spread of fire than non-natives. Economics is a factor too; where natives are planted for roadside weed control, savings have proven significant.
Saving Money and the Environment, Too
The benefits of preserving and growing native plants have become so widely accepted in the last two decades that 38 states have developed programs to protect and restore native vegetation. Caltrans has instituted a program of protecting native plants with special status that grow along its roads, but Texas has gone much farther by restoring to their natural splendor thousands of acres of thoroughfares that had been blighted by decades of herbicide spraying.
In Texas, where the state highway network is enormous, a program of planting native wildflowers has resulted thus far in a 25% reduction of roadside maintenance costs, saving about $8 million per year. Other benefits touted by Texans include increased wildlife habitat and biodiversity, improved erosion control, enhanced aesthetics, greater planting success with hardy natives and suppressed noxious weed invasions. Texas' program is also reputed to have strengthened community bonds between state agencies and citizen groups.
Meanwhile, at the University of Northern Iowa, a $760,000 appropriation from Congress is being used to expand a popular ten-year-old program to plant native grasses and flowers along roads administered by the Iowa Department of Transportation . Investing in the establishment of native plants has also paid off in reduced roadside maintenance costs in Iowa. By 1993, a decade into its statewide program, Iowa counties had cut costs for herbicide spraying by 70% - 90% and substantially reduced mowing and brush-control expenses.
A similar program in California could also cut costs dramatically - if funds were initially allocated to make the transition - since, once established, competitive vegetation requires much less maintenance. Unfortunately, Caltrans spent $200,000 to develop a computer database about the native plants that grow best in each locale but has not invested in a cost-comparison analysis of its various management options or even investigated how much money would be required to adequately launch a fully developed IVM program.
Not Natives, But Not Weeds Either
Planting natives may be the ideal way to establish competitive vegetation, but roadsides are harsh environments which may not support plants once indigenous to an area. Soil that is scraped and reconfigured during road construction is often completely altered in the roadside ecology and bears little resemblance to adjacent lands. Determinations of what species to plant, therefore, must balance the desire for absolute purity of native plants against the pragmatic mandates of road-management agencies.
It often may be necessary to cultivate non-native plants where roadsides have already become corrupted by surrounding industrial development or when native species compatible to the site are unavailable. But when non-native plants are used, great care must be taken in their selection to avoid costly mistakes that road agencies have made in the past. Earlier roadside plantings included invasive species that later developed into serious ecological problems.
Useful competitive vegetation species may include so-called allelopathic plants, species which have over the millennia developed toxic substances that inhibit the growth of competing vegetation by releasing toxins that kill, stunt or suppress germination of nearby plants and seeds.
Among the earliest recognized allelopathic plants are walnut trees and aromatic herbs such as sage, but theories about the existence of allelopathy as an aspect of plant behavior remained so controversial until recent years that research into ways to make use of it for weed control has only begun to receive serious attention from scientists.
Now the use of allelopathy for the control of weeds is at the cutting edge of environmentally sound weed management. It has been found that certain common turfgrasses, for example, inhibit the germination of various trees - a common roadside problem - and can survive drought, low soil fertility, heavy trampling and other conditions that regularly occur along well-traveled roads.
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