The battle of power lines and the urban forest
By Adrian Higgins,
Washington area residents tend to think about the metropolis’s imperfect system of electricity delivery when it fails, as it did spectacularly on the night of June 29 with the arrival of a broad, fast-moving storm we now know as a derecho.
Todd Bolton, as the arborist for Takoma Park, is mindful every day of the precarious coexistence of the urban forest and the power lines strung up on poles 25 to 35 feet in the air. On some corners in this historic little city, so many wires seem to be held aloft that you might think you are looking up to some mystical dreamcatcher, though one that seems to prefer collective nightmares at times of hurricanes, tornadoes, derechos, wind shears, ice storms and the occasional Snowmageddon.
We don’t perch domestic gas lines or water mains up in the elements — they’re snugly buried beneath the road — so why power cables? The short answer is that it’s expensive to bury them, but it has to do with history, too. Bolton eyed a map of Takoma Park on his desk computer that shows how the suburban community on the northern tip of the District grew from its incorporation in 1890.
Many of the city’s oldest neighborhoods received basic electricity supply in the first decades of the last century at a time when trees that grew from the mid-19th century were already of great height and girth. A single, innocuous power line brought power well below where these lofty giants began to branch. But during the course of the 20th century, homes became loaded with air conditioners, refrigerators, washer-dryers and other appliances, requiring an increasingly powerful network of electricity transmission and distribution. At the same time, new development led to wholesale removal of old trees and the planting of new ones that were destined to grow amid the utility wires.
Takoma Park, with its leafy neighborhoods of old houses, is like so many other communities of suburban Maryland, the District and Northern Virginia — cozy and settled but with an uneasy alliance of deciduous shade trees amid the aerial power grid. (Telephone and cable lines piggyback on the poles, themselves the carcasses of old pine trees.)
If you live in one of these neighborhoods, you don’t have to go far to see that in the struggle between shade trees and power lines, the trees might win the storm-by-storm battle, but they’re losing the war with the utility companies’ tree trimmers. In my neighborhood in Alexandria, which lost power for six days after the derecho, I can look out to an old oak tree whose central leader has been removed to leave lower branches that have turned skyward to the light to form a 60-foot “U.”
A few blocks away, there is a Chinese elm that has been rendered as a Texas longhorn. Nearby, two silver maples in someone’s front yard have lost their natural canopy, replaced by a towering, crescent-shaped hedge that curves around the power line of Dominion Virginia Power.
Check out Pepco’s Web site and you will find a guide to line clearance that sugarcoats the necessary butchery by conflating universally correct pruning techniques with dismemberment, namely the sawing off of a tree’s central leader or the removal of a whole side of a crown. This might be necessary to keep tree limbs away from lines, but it leaves the oak or maple or sweetgum — name the species — in a state of mutilation. The guide has wonderfully upbeat and persuasive language and compares the radical pruning regime with an older approach of topping trees — reducing a canopy to an arbitrary size. This worked for one season, until the tree responded with a mass of weak wooded shoots from the area of the cut — suckers or, more accurately, watersprouts.
Pepco is surely right when it says that sometimes it is better simply to remove the tree and rethink the equation, but others don’t necessarily agree, believing that a mutilated big tree still provides environmental benefits of providing shade to people and cooling the urban heat island.
Another complexity arises when the power company’s theory of skilled pruning doesn’t always translate into practice. Bolton took me to see a mature redbud to the side of a power line where a Pepco contractor took out the leader two years ago in a way that spawned a mess of suckers, “which absolutely defeated what they tried to do.”
The desire to do it right “doesn’t always get down to the minimum-wage guys in the bucket,” he said. Bolton also took me to the city’s swank Takoma Avenue, where a broad street runs between big lots with large, period houses.
On one end of the block, he pointed to two oaks, one 25 years old, the other 40, now disfigured where they had been cut away from the power line. “Somebody planted the wrong tree,” he said. At the other end of the block, he has installed a row of four Japanese flowering cherry trees that seem destined to coexist with the lines, at least for most of their lives.
This is an obvious solution: Get the local government to replace oversized shade or canopy trees with understory trees that reach between 20 and 30 feet at maturity. (See the accompanying list of suggested varieties.) These selections are the bailiwick of your local government. In the District, you can request the Department of Transportation to take down an ailing shade tree and replace it with an understory tree on the city’s Urban Forestry Administration-approved list. The smaller trees also make sense on private property that abuts power lines. Power companies have the right to cut back private trees that could interfere with lines.
Dominion Power (motto: “Look before you leaf”) doesn’t want any trees under its power lines, suggesting instead planting shrubs. I just don’t see folks wanting to get out of their cars to brush against spireas and viburnums.
Gradually replacing mutilated shade trees with understory trees solves one problem but creates others — one side of the street with 15-foot trees, the other side with 50-foot trees. Also, utility contractors have been known to cut back even the understory trees. In addition, the smaller trees don’t shade and cool as canopy trees do. “Planting small trees comes at an environmental cost,” said Maisie Hughes, director of planning and design for the District-based nonprofit Casey Trees.
Nor should we take down every shade tree that might fall on a power line, says Dean Amel, a member of Arlington County's Urban Forestry Commission. “I don’t think it’s reasonable. We wouldn’t be able to plant canopy trees pretty much anywhere in Arlington if that was the case.”
In Arlington, where the county government no longer plants trees on strips that are narrower than four feet, the answer might lie in getting residents to revegetate the urban forest on their land. The county funds tree planting on private property by community groups.
“We see private property as having the most area for large shade trees,” said Jamie Bartalon, forestry and landscape supervisor for the county parks department.
For District residents, Casey Trees works with the city to provide residents with shade trees for $50 — that’s a real bargain, by the way. Still, Hughes hankers for a world of grand old street trees without the worry of the power lines. “If we didn’t have [overhead] power lines, we could have these amazing oak-lined or elm-lined streets,” she said. (If you want to see such a canopy in the offing, check out the young disease-resistant varieties of American elm in front of the White House.)
Bolton says his ideal solution would be to bury the main lines when highway departments rebuild roads, reducing the aerial system to simple, localized power lines that need only three or four feet of tree clearance. “Then if they’re taken down, you only lose a block,” he said.
10 understory trees that coexist with power lines
Small, upright trees make great alternatives to old, mutilated shade trees that have lost their battle with overhead power lines and the utility company’s tree “trimmers.”
Municipal arborists call these alternatives “understory trees” because in nature the trees grow below the forest canopy. Pressed into street tree service, they need to be upright in habit and tolerant of all the ills of growing in a narrow curbside strip, among them poor soil, heat stress, limited root space and road salt.
The trees listed at the bottom of these pages also make good candidates on the edge of private lots where shade trees might, in time, grow into power lines.
Crape myrtles might seem a perfect choice but aren’t on my list: The popular variety Natchez grows to 30 feet with a 20 feet spread, and smaller, multi-stemmed varieties need skilled, annual pruning when young to create a tree form.
1. American hornbeam (Carpinus caroliniana): This small tree with beech-like leaves and silver bark deserves more use. Not a showy bloomer, it develops an upright rounded canopy and grows to a tidy 20 feet. The upright form of the European hornbeam is more common, used as a screen in tight spaces.
2. Crab apple (Malus): It is important to pick a variety that is both upright in growth habit and bred for disease resistance. The crab apple is gorgeous in bud, flower and fruit, though its dropped fruit can be messy. Suitable street tree varieties include Adirondack, Donald Wyman, Autumn Glory, Naragansett and Professor Sprenger, all white-flowering. Prairifire has magenta flowers. Takoma Park arborist Todd Bolton plants a variety named Thunderchild, a 15-footer with pink blossoms.
3. Eastern redbud (Cercis canadensis): This beloved native woodland tree functions nicely as a street tree, growing to 15 to 20 feet when pressed into curbside duty. Somewhat short-lived in a stressed environment, but worth replacing every 20 to 30 years.
4. Flowering cherry (Prunus): The classic Tidal Basin variety is Yoshino, fine for street use, rarely growing to more than 20 feet. Kwanzan, with magenta-pink double flowers, is another stalwart small street tree. Bolton also likes a newer variety named Snow Goose. White-flowered and upright, it grows to just 20 feet.
5. Flowering dogwood (Cornus florida): Like the redbud, this iconic native tree is unlikely to reach great, spreading age at the roadside. Particularly suited to front yards near power lines. Dogwood alternatives include the more upright and larger kousa dogwood (Cornus kousa).
6. Japanese tree lilac (Syringa reticulata): Upright, tree form of lilac that blooms in early June with white flowers. Not particularly fragrant, but a sturdy tree suited for street use.
7. Sweetbay magnolia (Magnolia virginiana): Small, native magnolia growing to 20 feet, with attractive gray-green leaves. The white blossoms appear in late spring. It likes moist conditions but can endure drought once established. An alternative is the entirely different magnolia Galaxy, stouter and symmetric but still sufficiently upright and short for street use. Its strong pink blooms appear in early spring.
8. Serviceberry (Amelanchier): Amelanchiers grow as large shrubs or small trees, depending on species and individual form. Select one that has a single trunk. Autumn Brilliance is a hybrid favored for its tree form and red fall color.
9. Trident maple (Acer buergeranum): Asian maple that grows to approximately 20 feet with great fall color. Woody plant expert Michael Dirr writes: “Small, dapper, handsomely clothed trees are a rarity, and trident maple qualifies as one of the best.” An alternative might be the paperbark maple (Acer griseum), slow growing, with beautiful peeling cinnamon bark, but hard to find and somewhat expensive.
10. Washington hawthorn (Crataegus phaenopyrum): Heat-tolerant species of hawthorn that grows to about 20 feet in a street setting. Princeton Sentry is a near-thornless variety. A suitable alternative is the Winter King variety of green hawthorn.