Environmental Impact of Herbicides on Electric Transmission Line Rights-Of-Way

Abstract

In 1972 Edison Electric Institute began a long-term study on the environmental impact of frequent herbicide application to electric transmission line rights-of-way. Transmission line areas at nine locations were selected: New. This distribution provided nationwide coverage with the heaviest concentration in those areas where herbicides are most used for vegetation control. The study areas in each state consist of a two-mile section of right-of-way where the spraying history is known. Each study line has nine permanent study plots representing moist, average, and dry sites. In addition, in each state studies were made of plant communities on adjacent unsprayed old fields. These off-right-of-way areas were used for comparing the artificial line communities with natural plant communities. Plant Community and Aesthetic Study For each study area a vegetation map was constructed showing those plant communities now present. Similar maps were also made of plant communities on unsprayed old fields. These maps give the boundaries of the herbaceous communities currently occupying the site, and the exact location, species and height of shrubs and woody plants. During mapping note was made of the occurrence and abundance of noxious weeds that might serve as an objectionable seed source for nearby agricultural lands. Plants poisonous to livestock were also identified. Partially-killed material was recorded, as well as open and eroding soil. Permanent photographic stations were established at many points so that a regular series of photographs could be obtained to follow seasonal changes as well as gradual changes in vegetation from one year to the next. Results Although there were differences between each geographic area, there were many similarities in the pattern of vegetational change from using herbicides over a decade or longer. Plant communities on blanket-sprayed rights-of-way differed markedly from communities on unsprayed areas. Herbicide communities are generally less dense and poorer in the number of perennials, particularly the showy summer and fall wildflowers, when compared to unsprayed old fields. Between each blanket spraying re-invasion of perennial plants begins, but is interrupted again by the next spraying. In those areas where picloram is used re-invasion is slower than where phenoxies are used. It was interesting to note that the spring wildflower population was similar on both line areas and old fields. As many of these plants complete their life cycle prior to the spraying season they are less affected by the spraying program. Where selective spraying is used, due to the smaller area actually treated by herbicide, there is much closer correlation between line communities and adjacent old fields. Present plant communities on blanket-sprayed areas are largely composed of species somewhat resistant to herbicides. Orderly changes are gradually taking place in the communities now present. Competition is severe between existing communities. The more resistant plants now present on these line areas are gradually spreading and driving-out other more sensitive species. Thus, over a long period a "herbicide climax" will develop and dominate these areas. This climax is made up of plants favored by the herbicide treatment. On selectively-sprayed areas the climax community that develops will differ in several ways from blanket-sprayed areas. Selectively-sprayed areas often contain a nucleus of showy shrubs that spread rapidly. Therefore, selective