Utility Arboriculture and Urban Requirements

Utility forestry dimensions

Utility forestry is primarily concerned with trees as they are affected by electrical power transmission and distribution. Telephone and related electronic service as well as cable television instrumentation are also essential to our North American lifestyle. Physical associations of these three services and tree branches as well as roots often become complicated. Installation and maintenance of all three services include tortuous subsurface and overhead routes. These corridors often parallel one another and can occupy numerous elevational levels and directions. Cost-wise, transmitting plus distributing electrical service as well as telephone and cable television transmission, is least expensive, at a ratio of one to eight when conducted through the wires of above-ground systems (10).

In most of Canada and the United States, electrical transmission along rights-of-way linking metropolitan and other urban areas implies high voltage currents of up to 765,000 volts. High voltage carriers can be visually recognized by their height and stature.

Vegetation management along these ranks of gargantuan towers connected by multiple, two-inch aluminum cables involves precisely regulated, managed greenspace. Management, in this case, emphasizes establishment and husbandry of low growing vegetative cover types. Powerline rights-of-way which traverse metropolitan areas can also include multi-purpose vegetation designs. On one hand, open land can support diverse populations of native grasses, shrubs and wildflowers as well as rented, vegetable garden plots. On the other hand, this dynamic land can also provide valuable songbird and wildlife habitat (3).

Management also involves precise tree pruning plus related silvicultural practices beneath the wires, and adjacent to designated rights-of-way. To avoid contact between vigorous woody vegetation and power lines, which would cause power outage, large trees are either pruned or removed.

Similar procedures to control vegetation are also practiced along low voltage distribution lines utilized at the backyard level. Power here is between the conventional 120 or 240 household voltage up to 34,000 volts for light industry. Union or juncture of this transmitting and distributing system can be recognized in the ur- banscape by gravelled transformer yards where connections are made between 100-foot steel towers and 30-foot wooden poles.

At the Illinois stratum, with its 10 million people, electrical power company expenditures are about $2.6 billion. Of this, $54 million is budgeted for utility forestry and arboricultural practices (2).

Illinois utility companies have the legal, statutory obligation to prune trees, on either public or private property, which are adjacent to distribution wires. They also adjust vegetation within, or growing into distribution line corridors. These corridors, often separating property lots are usually 6 to 10 and up to 15 feet wide and are found in all Illinois communities. Jurisdiction to adjust tree growth on public or private property is authorized by the Illinois Public Utilities Act and other regulations assigned by the Illinois Commerce Commission.

Recommendations

Electrical service can be improved to the homeowner if new trees are selected and planted properly. Most utility customers are aware that carefully pruned trees are beneficial to the service user and to the providing utility. However few customers recognize the importance of locating and planting trees correctly.

Careful selection and planting is a prime, preventative technique to keep the branches out of utility wires once the trees mature. Wise woody plant selection also helps to ensure reliable electric service while enhancing the home environment. Small ornamental trees that require little maintenance are highly recommended by nurserymen for urban right-of-way planting. Regardless of which tree the homeowner selects, the following guidelines should be kept in mind:

• Large shrubs expected to reach 15 feet or less at maturity may be planted beneath utility wires;

• Small trees which will not exceed 30 feet at maturity may be planted 15 feet or more from the wires to allow adequate space for future growth:

• Medium trees that range between 30 and 70 feet in height at maturity should be planted at least 35 feet away from overhead lines for sufficient growth space; and

• Large trees expected to reach beyond 70 feet at maturity should not be planted within 45 feet of overhead wires.

Besides the consideration that should be given to overhead and underground electric lines, the homeowner should also avoid planting any shrubs or trees near padmounted electrical equipment. This includes air conditioner compressors, electrical terminals and transfer cases or cable TV connecting facilities.

Summary

The challenge of providing safe electrical power while maintaining attractive urban landscapes, can be achieved. We can blend mounting electrical demands of our growing urban population with ecologically managed, adequately spaced greenery punctuated by shrubs and trees. Concerned citizens, responsive electrical utility organizations, municipal officials, and scientists are joining to create a further electrified community, well landscaped and vegetated.